AD7623ASTZRL [ADI]
16-Bit, 1.33 MSPS PulSAR ADC;
| 型号： | AD7623ASTZRL |
| 厂家： | 
ADI |
| 描述： | 16-Bit, 1.33 MSPS PulSAR ADC |
| 文件： | 总29页 (文件大小：444K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
16-Bit, 1.33 MSPS PulSAR® ADC
AD7623
FUNCTIONAL BLOCK DIAGRAM
FEATURES
TEMP REFBUFIN REF REFGND
DVDD DGND
Throughput: 1.33 MSPS
2.048 V internal reference
Differential input range: VREF (VREF up to 2.5 V)
INL: 1 LSB typical
AGND
AVDD
OVDD
OGND
AD7623
REF
REF AMP
16-bit resolution with no missing codes
SINAD: 88 dB typical @ 100 kHz
THD: −97 dB typical @ 100 kHz
No pipeline delay (SAR architecture)
Parallel (16- or 8-bit bus) and serial 5 V/3.3 V/2.5 V interface
SPI®-/QSPI™-/MICROWIRE™-/DSP-compatible
2.5 V single-supply operation
Power dissipation: 45 mW typical @ 1.33 MSPS
48-lead LQFP and LFCSP_VQ packages
Speed upgrade of the AD7677
SERIAL
PORT
16
IN+
IN–
SWITCHED
CAP DAC
D[15:0]
SER/PAR
BUSY
PARALLEL
INTERFACE
PDREF
PDBUF
PD
RD
CLOCK
CS
CONTROL LOGIC AND
CALIBRATION CIRCUITRY
OB/2C
BYTESWAP
RESET
CNVST
Figure 1.
APPLICATIONS
Table 1. PulSAR Selection
Medical instruments
High speed data acquisition
Digital signal processing
Communications
Instrumentation
800 to
100 to 250 500 to 570 1000
AD7651 AD7650/52 AD7653
AD7660/61 AD7664/66 AD7667
Type/kSPS
>1000
Pseudo
Differential
True Bipolar
AD7663
AD7675
AD7665
AD7676
AD7671
Spectrum analysis
ATE
AD7677 AD7621
AD7623
True
Differential
18-Bit
Multichannel/
Simultaneous
AD7678
AD7679
AD7654
AD7674 AD7641
AD7655
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
1. Fast Throughput.
The AD7623 is a 16-bit, 1.33 MSPS, charge redistribution SAR,
fully differential analog-to-digital converter (ADC) that
operates from a single 2.5 V power supply. It contains a high
speed 16-bit sampling ADC, an internal conversion clock, an
internal reference (and buffer), error correction circuits, and
both serial and parallel system interface ports. Power consump-
tion is automatically scaled with throughput, making it ideal
for battery-powered applications. It is available in 48-lead, low
profile quad flat package (LQFP) and a lead frame chip-scale
(LFCSP_VQ) package. Operation is specified from
The AD7623 is a 1.33 MSPS, charge redistribution,
16-bit SAR ADC.
2. Superior Linearity.
The AD7623 has no missing 16-bit code.
3. Internal Reference.
The AD7623 has a 2.048 V internal reference with a
typical drift of 7 ppm/°C.
4. Single-Supply Operation.
The AD7623 operates from a 2.5 V single supply and
typically dissipates 45 mW. Its power dissipation decreases
with the throughput.
−40°C to +85°C.
5. Serial or Parallel Interface.
Versatile parallel (16- or 8-bit bus) or 2-wire serial interface
arrangement compatible with 2.5 V, 3.3 V, or 5 V logic.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
© 2005 Analog Devices, Inc. All rights reserved.
AD7623* PRODUCT PAGE QUICK LINKS
Last Content Update: 04/14/2017
COMPARABLE PARTS
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DESIGN RESOURCES
• AD7623 Material Declaration
• PCN-PDN Information
• Quality And Reliability
• Symbols and Footprints
EVALUATION KITS
• AD7623 Evaluation Kit
DOCUMENTATION
Application Notes
DISCUSSIONS
View all AD7623 EngineerZone Discussions.
• AN-931: Understanding PulSAR ADC Support Circuitry
• AN-932: Power Supply Sequencing
Data Sheet
SAMPLE AND BUY
Visit the product page to see pricing options.
• AD7623: 16-Bit, 1.33 MSPS PulSAR® ADC Data Sheet
TECHNICAL SUPPORT
TOOLS AND SIMULATIONS
• AD7623 IBIS Models
Submit a technical question or find your regional support
number.
DOCUMENT FEEDBACK
Submit feedback for this data sheet.
REFERENCE MATERIALS
Technical Articles
• MS-2210: Designing Power Supplies for High Speed ADC
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AD7623
TABLE OF CONTENTS
Features .............................................................................................. 1
Analog Inputs ............................................................................. 17
Driver Amplifier Choice ........................................................... 17
Voltage Reference Input ............................................................ 18
Power Supply............................................................................... 19
Power Dissipation vs. Throughput .......................................... 20
Conversion Control ................................................................... 20
Interfaces.......................................................................................... 21
Digital Interface.......................................................................... 21
Parallel Interface......................................................................... 21
Serial Interface............................................................................ 22
Master Serial Interface............................................................... 22
Slave Serial Interface .................................................................. 24
Microprocessor Interfacing....................................................... 26
Application ...................................................................................... 27
Layout .......................................................................................... 27
Evaluating the AD7623 Performance...................................... 27
Outline Dimensions....................................................................... 28
Ordering Guide .......................................................................... 28
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description......................................................................... 1
Product Highlights ........................................................................... 1
Specifications..................................................................................... 3
Timing Specifications....................................................................... 5
Serial Clock Timing Specifications............................................ 6
Absolute Maximum Ratings............................................................ 7
ESD Caution.................................................................................. 7
Pin Configuration and Function Descriptions............................. 8
Terminology .................................................................................... 11
Typical Performance Characteristics ........................................... 12
Theory of Operation ...................................................................... 15
Circuit Information.................................................................... 15
Converter Operation.................................................................. 15
Transfer Functions...................................................................... 16
Typical Connection Diagram ................................................... 17
REVISION HISTORY
7/05—Revision 0: Initial Version
Rev. 0 | Page 2 of 28
AD7623
SPECIFICATIONS
AVDD = DVDD = 2.5 V; OVDD = 2.3 V to 3.6 V; VREF = 2.5 V; all specifications TMIN to TMAX, unless otherwise noted.
Table 2.
Parameter
Conditions
Min
Typ
Max
Unit
RESOLUTION
16
Bits
ANALOG INPUT
Voltage Range
−VREF
−0.1
+VREF
AVDD1
V
VIN+ − VIN−
VIN+, VIN− to AGND
fIN = 100 kHz
Operating Input Voltage
Analog Input CMRR
Input Current
V
dB
μA
55
10
1.33 MSPS throughput
Input Impedance2
THROUGHPUT SPEED
Complete Cycle
750
ns
Throughput Rate
0
1.33
MSPS
DC ACCURACY
Integral Linearity Error3
No Missing Codes
Differential Linearity Error
Transition Noise
Transition Noise
VREF = 2.048 V, PDREF = high
VREF = 2.048 V, PDREF = high
VREF = 2.048 V, PDREF = high
VREF = 2.5 V
−2
16
−1
1
+2
+2
LSB4
Bits
LSB
LSB
LSB
LSB
0.70
0.82
VREF = 2.048 V
5
Zero Error, TMIN to TMAX
−30
+30
Zero Error Temperature Drift
Gain Error, TMIN to TMAX
Gain Error Temperature Drift
Power Supply Sensitivity
AC ACCURACY
1
ppm/°C
% of FSR
ppm/°C
LSB
5
−0.38
+0.38
2
2
AVDD = 2.5 V 5%
Dynamic Range
Signal-to-Noise
fIN = 20 kHz
fIN = 20 kHz
fIN = 20 kHz, VREF = 2.048 V
fIN = 100 kHz
fIN = 20 kHz
fIN = 100 kHz
fIN = 20 kHz
fIN = 100 kHz
fIN = 20 kHz
90
89.5
88
89
97
dB6
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
MHz
88
86
Spurious-Free Dynamic Range
Total Harmonic Distortion
96
–97
−95
88.5
87.5
88
Signal-to-(Noise + Distortion)
87.5
fIN = 20 kHz, VREF = 2.048 V
fIN = 100 kHz
–3 dB Input Bandwidth
SAMPLING DYNAMICS
Aperture Delay
50
1
5
ns
ps rms
ns
Aperture Jitter
Transient Response
INTERNAL REFERENCE
Output Voltage
Temperature Drift
Line Regulation
Turn-On Settling Time
REFBUFIN Output Voltage
REFBUFIN Output Resistance
Full-scale step
50
PDREF = PDBUF = low
REF @ 25°C
–40°C to +85°C
AVDD = 2.5 V 5%
CREF = 10 μF
2.038
2.048
7
15
5
1.2
6.33
2.058
V
ppm/°C
ppm/V
ms
V
kΩ
REFBUFIN @ 25°C
Rev. 0 | Page 3 of 28
AD7623
Parameter
Conditions
Min
Typ
Max
Unit
EXTERNAL REFERENCE
Voltage Range
Current Drain
REFERENCE BUFFER
REFBUFIN Input Voltage Range
TEMPERATURE PIN
Voltage Output
Temperature Sensitivity
Output Resistance
DIGITAL INPUTS
Logic Levels
PDREF = PDBUF = high
REF
1.33 MSPS throughput
PDREF = high, PDBUF = low
1.8
2.048
100
AVDD
V
μA
1.05
1.2
1.30
V
@ 25°C
273
0.85
4.7
mV
mV/°C
kΩ
VIL
VIH
IIL
IIH
–0.3
1.7
–1
+0.6
5.25
+1
V
V
μA
μA
–1
+1
DIGITAL OUTPUTS
Data Format7
Pipeline Delay8
VOL
ISINK = 500 μA
ISOURCE = –500 μA
0.4
V
V
VOH
OVDD − 0.3
POWER SUPPLIES
Specified Performance
AVDD
2.37
2.37
2.309
2.5
2.5
2.63
2.63
3.6
V
V
V
DVDD
OVDD
Operating Current10
AVDD11
DVDD
1.33 MSPS throughput
With internal reference
15
1.6
0.6
mA
mA
mA
OVDD
Power Dissipation10
With Internal Reference11
Without Internal Reference11
In Power-Down Mode12
TEMPERATURE RANGE13
Specified Performance
1.33 MSPS throughput
1.33 MSPS throughput
PD = high
50
45
600
55
53
mW
mW
μW
TMIN to TMAX
–40
+85
°C
1 When using an external reference. With the internal reference, the input range is from −0.1 V to VREF
2 See the Analog Inputs section.
.
3 Linearity is tested using endpoints, not best fit. Tested with an external reference at 2.048 V.
4 LSB means least significant bit. With the 2.048 V input range, 1 LSB is 62.5 μV.
5 See the Terminology section. These specifications do not include the error contribution from the external reference.
6 All specifications in dB are referred to a full-scale input FSR. Tested with an input signal at 0.5 dB below full-scale, unless otherwise specified.
7 Parallel or serial 16-bit.
8 Conversion results are available immediately after completed conversion.
9 See the Absolute Maximum Ratings section.
10 Tested in parallel reading mode.
11 With internal reference, PDREF and PDBUF are low; without internal reference, PDREF and PDBUF are high.
12 With all digital inputs forced to OVDD.
13 Consult sales for extended temperature range.
Rev. 0 | Page 4 of 28
AD7623
TIMING SPECIFICATIONS
AVDD = DVDD = 2.5 V; OVDD = 2.3 V to 3.6 V; VREF = 2.5 V; all specifications TMIN to TMAX, unless otherwise noted.
Table 3.
Parameter
Symbol Min
Typ
Max
Unit
CONVERSION AND RESET (Refer to Figure 31 and Figure 32)
Convert Pulse Width
Time Between Conversions
CNVST Low to BUSY High Delay
BUSY High All Modes (Except Master Serial Read After Convert)
Aperture Delay
End of Conversion to BUSY Low Delay
Conversion Time
t1
t2
t3
t4
t5
t6
t7
t8
t9
t38
t39
15
750
701
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
23
560
1
10
560
560
Acquisition Time
RESET Pulse Width
125
15
RESET Low to BUSY High Delay2
BUSY High Time from RESET Low2
PARALLEL INTERFACE MODES (Refer to Figure 33 to Figure 35).
CNVST Low to DATA Valid Delay
DATA Valid to BUSY Low Delay
Bus Access Request to DATA Valid
Bus Relinquish Time
10
600
t10
t11
t12
t13
ns
ns
ns
ns
2
2
20
15
MASTER SERIAL INTERFACE MODES3 (Refer to Figure 37 and Figure 38)
CS Low to SYNC Valid Delay
t14
t15
t16
t17
t18
t19
t20
t21
t22
t23
t24
t25
t26
t27
t28
t29
t30
10
10
10
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
CS Low to Internal SCLK Valid Delay3
CS Low to SDOUT Delay
CNVST Low to SYNC Delay
263
SYNC Asserted to SCLK First Edge Delay
Internal SCLK Period4
0.5
8
2
3
1
12
Internal SCLK High4
Internal SCLK Low4
SDOUT Valid Setup Time4
SDOUT Valid Hold Time4
0
0
SCLK Last Edge to SYNC Delay4
CS High to SYNC HI-Z
10
10
10
CS High to Internal SCLK HI-Z
CS High to SDOUT HI-Z
BUSY High in Master Serial Read after Convert4
CNVST Low to SYNC Asserted Delay
SYNC Deasserted to BUSY Low Delay
SLAVE SERIAL INTERFACE MODES3 (Refer to Figure 40 and Figure 41)
External SCLK Setup Time
External SCLK Active Edge to SDOUT Delay
SDIN Setup Time
SDIN Hold Time
See Table 4
500
13
ns
ns
t31
t32
t33
t34
t35
t36
t37
5
1
5
5
12.5
5
5
ns
ns
ns
ns
ns
ns
ns
8
External SCLK Period
External SCLK High
External SCLK Low
1 See the Conversion Control section.
2 See the Digital Interface and RESET sections.
3 In serial interface modes, the SYNC, SCLK, and SDOUT timings are defined with a maximum load CL of 10 pF; otherwise, the load is 60 pF maximum.
4 In serial master read during convert mode. See Table 4 for serial master read after convert mode timing specifications.
Rev. 0 | Page 5 of 28
AD7623
SERIAL CLOCK TIMING SPECIFICATIONS
Table 4. Serial Clock Timings in Master Read After Convert Mode
DIVSCLK[1]
0
0
1
1
DIVSCLK[0]
Symbol
0
1
0
1
Unit
ns
ns
ns
ns
ns
ns
ns
ns
SYNC to SCLK First Edge Delay Minimum
Internal SCLK Period Minimum
Internal SCLK Period Maximum
Internal SCLK High Minimum
Internal SCLK Low Minimum
SDOUT Valid Setup Time Minimum
SDOUT Valid Hold Time Minimum
SCLK Last Edge to SYNC Delay Minimum
BUSY High Width Maximum
t18
t19
t19
t20
t21
t22
t23
t24
t28
0.5
8
12
2
3
1
0
0
3
3
3
16
25
6
7
5
0.5
0.5
1.000
32
50
15
16
5
10
9
1.440
64
100
31
32
5
28
26
2.320
0.780
μs
500μA
I
OL
TO OUTPUT
PIN
1.4V
C
L
50pF
2V
500μA
I
OH
0.8V
tDELAY
NOTE
tDELAY
IN SERIAL INTERFACE MODES, THE SYNC, SCLK, AND
SDOUT ARE DEFINED WITH A MAXIMUM LOAD.
2V
0.8V
2V
C
OF 10pF; OTHERWISE, THE LOAD IS 60pF MAXIMUM.
0.8V
L
Figure 2. Load Circuit for Digital Interface Timing,
SDOUT, SYNC, and SCLK Outputs, CL = 10 pF
Figure 3. Voltage Reference Levels for Timing
Rev. 0 | Page 6 of 28
AD7623
ABSOLUTE MAXIMUM RATINGS
Table 5.
Parameter
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rating
Analog Inputs/Outputs
IN+1, IN−, REF, REFBUFIN, TEMP,
INGND, REFGND to AGND
Ground Voltage Differences
AGND, DGND, OGND
Supply Voltages
AVDD + 0.3 V to
AGND − 0.3 V
0.3 V
AVDD, DVDD
OVDD
AVDD to DVDD
–0.3 V to +2.7 V
–0.3 V to +3.8 V
2.8 V
AVDD to OVDD
+2.8 V to −3.8 V
≤ +0.3 V if DVDD < 2.3 V
−0.3 V to +5.5 V
20 mA
OVDD to DVDD2
Digital Inputs
PDREF, PDBUF3
Internal Power Dissipation4
Internal Power Dissipation5
Junction Temperature
Storage Temperature Range
700 mW
2.5 W
125°C
–65°C to +125°C
1 See the Analog Inputs section.
2 See the Power Supply section.
3 See the Voltage Reference Input section.
4 Specification is for the device in free air: 48-Lead LQFP; θJA = 91°C/W,
θ
JC = 30°C/W.
5 Specification is for the device in free air: 48-Lead LFCSP; θJA = 26°C/W.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate
on the human body and test equipment and can discharge without detection. Although this product
features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to
high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid
performance degradation or loss of functionality.
Rev. 0 | Page 7 of 28
AD7623
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
48 47 46 45 44 43 42 41 40 39 38 37
1
2
AGND
AVDD
36 AGND
35 CNVST
34 PD
PIN 1
IDENTIFIER
3
NC
BYTESWAP
OB/2C
4
33
RESET
5
32 CS
AD7623
DGND
6
31
30
29
28
27
26
25
RD
TOP VIEW
DGND
7
DGND
BUSY
D15
(Not to Scale)
8
SER/PAR
9
D0
D1
10
11
12
D14
D2/DIVSCLK[0]
D3/DIVSCLK[1]
D13
D12
13 14 15 16 17 18 19 20 21 22 23 24
NC = NO CONNECT
Figure 4. Pin Configuration
Table 6. Pin Function Descriptions
Pin No.
1, 41, 42
2, 44
Mnemonic
Type1 Description
AGND
AVDD
NC
P
P
Analog Power Ground Pin.
Input Analog Power Pins. Nominally 2.5 V.
No Connect.
3, 40
4
BYTESWAP
DI
DI
Parallel Mode Selection (8-Bit/16-Bit). When high, the LSB is output on D[15:8] and the MSB is output
on D[7:0]; when low, the LSB is output on D[7:0] and the MSB is output on D[15:8].
Straight Binary/Binary Twos Complement Output. When high, the digital output is straight binary;
when low, the MSB is inverted resulting in a twos complement output from its internal shift register.
5
OB/2C
6, 7
8
DGND
SER/PAR
P
DI
Digital Power Ground.
Serial/Parallel Selection Input. When high, the serial interface is selected and some bits of the data bus
are used as a serial port; the remaining data bits are high impedance outputs. When SER/PAR = low,
the parallel port is selected.
9, 10
11, 12
D[0:1]
D[2:3]
DO
DI/O
Bit 0 and Bit 1 of the Parallel Port Data Output Bus.
When SER/PAR = low, these outputs are used as Bit 2 and Bit 3 of the parallel port data output bus.
or
When SER/PAR = high, serial clock division selection. When using serial master read after convert
mode (EXT/INT = low, RDC/SDIN = low), these inputs can be used to slow down the internally
generated serial clock that clocks the data output. In other serial modes, these pins are high
impedance outputs.
DIVSCLK[0:1]
13
D4
DI/O
When SER/PAR = low, this output is used as Bit 4 of the parallel port data output bus.
or EXT/INT
When SER/PAR = high, serial clock source select. This input is used to select the internally generated
(master ) or external (slave) serial data clock.
When EXT/INT = low, master mode. The internal serial clock is selected on SCLK output.
When EXT/INT = high, slave mode. The output data is synchronized to an external clock signal, gated
by CS, connected to the SCLK input.
14
15
D5
DI/O
DI/O
When SER/PAR = low, this output is used as Bit 5 of the parallel port data output bus.
or INVSYNC
When SER/PAR = high, invert sync select. In serial master mode (EXT/INT = low), this input is used to
select the active state of the SYNC signal.
When INVSYNC = low, SYNC is active high.
When INVSYNC = high, SYNC is active low.
D6
PAR
When SER/
= low, this output is used as Bit 6 of the parallel port data output bus.
or INVSCLK
Invert SCLK Select. In all serial modes, this input is used to invert the SCLK signal.
Rev. 0 | Page 8 of 28
AD7623
Pin No.
Mnemonic
D7
or RDC
Type1 Description
16
DI/O
Bit 7 of the Parallel Port Data Output Bus.
When SER/PAR = high, read during convert. When using serial master mode (EXT/INT = low), RDC is
used to select the read mode.
When RDC = high, the previous conversion result is read during current conversion and the period of
SCLK changes (see the Master Serial Interface section).
When RDC = low (read after convert), the current result is read after conversion.
or SDIN
Serial Data In. When using serial slave mode, (EXT/INT = high), SDIN could be used as a data input to
daisy-chain the conversion results from two or more ADCs onto a single SDOUT line. The digital data
level on SDIN is output on SDOUT with a delay of 16 SCLK periods after the initiation of the read
sequence.
17
18
OGND
OVDD
P
P
Input/Output Interface Digital Power Ground.
Input/Output Interface Digital Power. Nominally at the same supply as the supply of the host interface
(2.5 V or 3 V).
19
20
21
DVDD
DGND
D8
P
P
DO
Digital Power. Nominally at 2.5 V.
Digital Power Ground.
When SER/PAR = low, this output is used as Bit 8 of the parallel port data output bus.
or SDOUT
When SER/PAR = high, serial data output. In serial mode, this pin is used as the serial data output
synchronized to SCLK. Conversion results are stored in an on-chip register. The AD7623 provides the
conversion result, MSB first, from its internal shift register. The data format is determined by the logic
level of OB/2C.
In master mode, (EXT/INT = low). SDOUT is valid on both edges of SCLK.
In slave mode, (EXT/INT = high):
When INVSCLK = low, SDOUT is updated on SCLK rising edge and valid on the next falling edge.
When INVSCLK = high, SDOUT is updated on SCLK falling edge and valid on the next rising edge.
22
23
D9
DI/O
DO
Parallel Port Data Output Bus Bit 9. When SER/PAR = low, this output is used as Bit 9 of the parallel port
data output bus.
Serial Clock. When SER/PAR = high, serial clock. In all serial modes, this pin is used as the serial data
clock input or output, dependent on the logic state of the EXT/INT pin. The active edge where the data
SDOUT is updated depends on the logic state of the INVSCLK pin.
or SCLK
D10
When SER/PAR = low, this output is used as Bit 10 of the parallel port data output bus.
or SYNC
When SER/PAR = high, frame synchronization. In serial master mode (EXT/INT= low), this output is
used as a digital output frame synchronization for use with the internal data clock.
When a read sequence is initiated and INVSYNC = low, SYNC is driven high and remains high while
SDOUT output is valid.
When a read sequence is initiated and INVSYNC = high, SYNC is driven low and remains low while
SDOUT output is valid.
24
D11
DO
Parallel Port Data Output Bus Bit 11. When SER/PAR = low, this output is used as Bit 11 of the parallel
port data output bus.
or RDERROR
Read Error. When SER/PAR = high, read error. In serial slave mode (EXT/INT = high), this output is used
as an incomplete read error flag. If a data read is started and not completed when the current
conversion is complete, the current data is lost and RDERROR is pulsed high.
25 to 28
29
D[12:15]
BUSY
DO
DO
Bit 12 to Bit 15 of the Parallel Port Data Output Bus.
Busy Output. Transitions high when a conversion is started, and remains high until the conversion is
complete and the data is latched into the on-chip shift register. The falling edge of BUSY can be used
as a data ready clock signal.
30
31
DGND
RD
P
DI
Digital Power Ground.
Read Data. When CS and RD are both low, the interface parallel or serial output bus is enabled.
32
33
CS
DI
DI
CS
Chip Select. When CS and RD are both low, the interface parallel or serial output bus is enabled. is
also used to gate the external clock in slave serial mode.
RESET
Reset Input. When high, reset the AD7623. Current conversion if any is aborted. Falling edge of RESET
enables the calibration mode indicated by pulsing BUSY high. Refer to the Digital Interface section. If
not used, this pin can be tied to DGND.
34
PD
DI
Power-Down Input. When high, power down the ADC. Power consumption is reduced and conversions
are inhibited after the current one is completed.
Rev. 0 | Page 9 of 28
AD7623
Pin No.
Mnemonic
Type1 Description
35
CNVST
DI
Conversion Start. A falling edge on CNVST puts the internal sample-and-hold into the hold state and
initiates a conversion.
36
37
AGND
REF
P
AI/O
Analog Power Ground Pin.
Reference Output/Input.
When PDREF/PDBUF = low, the internal reference and buffer are enabled, producing 2.048 V on this pin.
When PDREF/PDBUF = high, the internal reference and buffer are disabled, allowing an externally
supplied voltage reference up to AVDD volts. Decoupling is required with or without the internal
reference and buffer. Refer to the Voltage Reference Input section.
38
39
43
45
46
REFGND
IN−
IN+
TEMP
REFBUFIN
AI
AI
AI
AO
AI/O
Reference Input Analog Ground.
Differential Negative Analog Input.
Differential Positive Analog Input.
Temperature Sensor Analog Output.
Internal Reference Output/Reference Buffer Input.
When PDREF/PDBUF = low, the internal reference and buffer are enabled, producing the 1.2 V (typical)
band gap output on this pin, which needs external decoupling. The internal fixed gain reference buffer
uses this to produce 2.048V on the REF pin.
When using an external reference with the internal reference buffer (PDBUF = low, PDREF = high),
applying 1.2 V on this pin produces 2.048 V on the REF pin. Refer to the Voltage Reference Input section.
47
48
PDREF
PDBUF
DI
DI
Internal Reference Power-Down Input.
When low, the internal reference is enabled.
When high, the internal reference is powered down, and an external reference must be used.
Internal Reference Buffer Power-Down Input.
When low, the buffer is enabled (must be low when using internal reference).
When high, the buffer is powered-down.
1 AI = analog input; AI/O = bidirectional analog; AO = analog output; DI = digital input; DI/O = bidirectional digital; DO = digital output; P = power.
Rev. 0 | Page 10 of 28
AD7623
TERMINOLOGY
Integral Nonlinearity Error (INL)
Signal-to-(Noise + Distortion) Ratio (SINAD)
Linearity error refers to the deviation of each individual code
from a line drawn from negative full-scale through positive full-
scale. The point used as negative full-scale occurs ½ LSB before
the first code transition. Positive full-scale is defined as a level
1½ LSBs beyond the last code transition. The deviation is
measured from the middle of each code to the true straight line.
SINAD is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below the Nyquist
frequency, including harmonics but excluding dc. The value for
SINAD is expressed in decibels.
Spurious-Free Dynamic Range (SFDR)
The difference, in decibels (dB), between the rms amplitude of
the input signal and the peak spurious signal.
Differential Nonlinearity Error (DNL)
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing
codes are guaranteed.
Effective Number of Bits (ENOB)
ENOB is a measurement of the resolution with a sine wave
input. It is related to SINAD and is expressed in bits by
ENOB = [(SINADdB − 1.76)/6.02]
Gain Error
Aperture Delay
Aperture delay is a measure of the acquisition performance
measured from the falling edge of the
the input signal is held for a conversion.
The first transition (from 000…00 to 000…01) should occur for
an analog voltage ½ LSB above the nominal negative full-scale
(−2.0479688 V for the 2.048 V range). The last transition
(from 111…10 to 111…11) should occur for an analog voltage
1½ LSBs below the nominal full-scale (2.0479531 V for the
2.048 V range). The gain error is the deviation of the
difference between the actual level of the last transition and the
actual level of the first transition from the difference between
the ideal levels.
CNVST
input to when
Transient Response
The time required for the AD7623 to achieve its rated accuracy
after a full-scale step function is applied to its input.
Reference Voltage Temperature Coefficient
Reference voltage temperature coefficient is derived from the
typical shift of output voltage at 25°C on a sample of parts at the
Zero Error
The zero error is the difference between the ideal midscale
input voltage (0 V) and the actual voltage producing the
midscale output code.
maximum and minimum reference output voltage (VREF
)
measured at TMIN, T(25°C), and TMAX. It is expressed in ppm/°C as
V
REF (Max)–VREF (Min)
Dynamic Range
TCVREF (ppm/°C) =
where:
×106
VREF (25°C) × (TMAX –TMIN
)
Dynamic range is the ratio of the rms value of the full-scale to
the rms noise measured with the inputs shorted together. The
value for dynamic range is expressed in decibels.
V
V
V
REF (Max) = maximum VREF at TMIN, T (25°C), or TMAX.
REF (Min) = minimum VREF at TMIN, T (25°C), or TMAX
.
Signal-to-Noise Ratio (SNR)
REF (25°C) = VREF at 25°C.
SNR is the ratio of the rms value of the actual input signal to the
rms sum of all other spectral components below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
T
T
MAX = +85°C.
MIN = –40°C.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of the first five harmonic
components to the rms value of a full-scale input signal and is
expressed in decibels.
Rev. 0 | Page 11 of 28
AD7623
TYPICAL PERFORMANCE CHARACTERISTICS
1.5
1.0
2.0
1.5
1.0
0.5
0.5
0
0
–0.5
–1.0
–1.5
–2.0
–0.5
–1.0
0
16384
32768
CODE
49152
65536
0
16384
32768
CODE
49152
65536
Figure 8. Differential Nonlinearity vs. Code
Figure 5. Integral Nonlinearity vs. Code
160k
140k
120k
100k
80k
60k
40k
20k
0
160k
140k
120k
100k
80k
60k
40k
20k
0
147157
σ
= 0.82
σ
= 0.70
126114
62565
59008
58814
50472
7217
5928
2406
2258
168
0
119
1
0
11
2
0
7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
CODE IN HEX
7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
CODE IN HEX
Figure 9. Histogram of 261,120 Conversions of a DC Input
at the Code Center (Internal Reference)
Figure 6. Histogram of 261,120 Conversions of a DC Input
at the Code Center (External 2.5V Reference)
10
8
2.0530
2.0525
2.0520
2.0515
2.0510
2.0505
2.0500
2.0495
2.0490
2.0485
2.0480
6
4
2
–FS
0
–2
ZERO
ERROR
–4
–6
+FS
–8
–10
–55
–35
–15
5
25
45
65
85
105
125
–55
–35
–15
5
25
45
65
85
105
125
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 10. Zero Error, Positive and Negative Full Scale vs. Temperature
Figure 7. Typical Reference Voltage Output vs. Temperature (3 Units)
Rev. 0 | Page 12 of 28
AD7623
0
–20
0
–20
fS = 1.33MSPS
fIN = 20.03kHz
SNR = 89.4dB
THD = –104.1dB
SFDR = 107.2dB
SINAD = 89.3dB
fS = 1.33MSPS
fIN = 100.13kHz
SNR = 89.2dB
THD = –95.6dB
SFDR = 96dB
SINAD = 88.4dB
–40
–40
–60
–60
–80
–80
–100
–120
–140
–160
–180
–100
–120
–140
–160
–180
0
100
200
300
400
500
600
0
100
200
300
400
500
600
FREQUENCY (kHz)
FREQUENCY (kHz)
Figure 14. FFT 100 kHz
Figure 11. FFT 20 kHz
90
15.5
92
15.4
SNR
89
88
87
86
85
84
83
82
90
88
86
84
82
15.0
14.6
14.2
13.8
13.4
15.0
14.5
14.0
13.5
SNR
SINAD
ENOB
SINAD
ENOB
–55
–35
–15
5
25
45
65
85
105
125
1
10
100
1000
TEMPERATURE (°C)
FREQUENCY (kHz)
Figure 15. SNR, SINAD, and ENOB vs. Temperature
Figure 12. SNR, SINAD and ENOB vs. Frequency
–80
–85
100
95
90
85
80
75
70
65
60
55
50
–70
–75
120
110
100
90
SFDR
–90
SFDR
–80
THD
–95
–85
THIRD
–100
–105
–110
–115
–120
–125
–130
–90
80
HARMONIC
THD
70
–95
THIRD
HARMONIC
60
–100
–105
–110
–115
–120
SECOND
HARMONIC
50
40
SECOND
HARMONIC
30
20
1000
–55
–35
–15
5
25
45
65
85
105
125
1
10
100
TEMPERATURE (°C)
FREQUENCY (kHz)
Figure 16. THD, Harmonics, and SFDR vs. Temperature
Figure 13. THD, Harmonics, and SFDR vs. Frequency
Rev. 0 | Page 13 of 28
AD7623
91.0
100k
10k
1k
PDREF = PDBUF = HIGH
90.5
90.0
89.5
SNR
SINAD
AVDD
100
10
OVDD = 3.3V
DVDD
OVDD, 2.5V
100M
1
89.0
–60
0.1
10
–50
–40
–30
–20
–10
0
100
1k
10k
1M
10M
INPUT LEVEL (dB)
SAMPLING RATE (SPS)
Figure 17. SNR and SINAD vs. Input Level (Referred to Full Scale)
Figure 19. Operating Currents vs. Sample Rate
20
16
14
12
10
8
280
270
260
250
240
230
220
210
200
OVDD = 2.5V @ 85°C
18
16
14
12
10
8
OVDD = 2.5V @ 25°C
AVDD
OVDD, 3.3V
OVDD, 2.5V
OVDD = 3.3V @ 85°C
OVDD = 3.3V @ 25°C
6
4
6
2
DVDD
105
4
0
–55
0
50
100
C
150
200
–35
–15
5
25
45
65
85
125
(pF)
TEMPERATURE (°C)
L
Figure 18. Power-Down Operating Currents vs. Temperature
Figure 20. Typical Delay vs. Load Capacitance CL
Rev. 0 | Page 14 of 28
AD7623
THEORY OF OPERATION
IN+
AGND
LSB
SWITCHES
CONTROL
SW+
MSB
32,768C 16,384C
4C
4C
2C
2C
C
C
C
C
BUSY
REF
CONTROL
LOGIC
COMP
REFGND
OUTPUT
CODE
32,768C 16,384C
MSB
SW–
LSB
CNVST
AGND
IN–
Figure 21. ADC Simplified Schematic
CIRCUIT INFORMATION
During the acquisition phase, terminals of the array tied to the
comparator’s input are connected to AGND via SW+ and SW−.
All independent switches are connected to the analog inputs.
Thus, the capacitor arrays are used as sampling capacitors and
acquire the analog signal on IN+ and IN− inputs. A conversion
phase is initiated once the acquisition phase is complete and the
The AD7623 is a very fast, low power, single-supply, precise,
16-bit analog-to-digital converter (ADC) using successive
approximation architecture. The AD7623 is capable of
converting 1,330,000 samples per second (1.33 MSPS).
The AD7623 provides the user with an on-chip track-and-hold,
successive approximation ADC that does not exhibit any
pipeline or latency, making it ideal for multiple multiplexed
channel applications.
CNVST
input goes low. When the conversion phase begins,
SW+ and SW− are opened first. The two capacitor arrays are
then disconnected from the inputs and connected to the
REFGND input. Therefore, the differential voltage between the
inputs (IN+ and IN−) captured at the end of the acquisition
phase is applied to the comparator inputs, causing the
comparator to become unbalanced. By switching each element
of the capacitor array between REFGND and REF, the
comparator input varies by binary weighted voltage steps
(VREF/2, VREF/4 through VREF/65536). The control logic toggles
these switches, starting with the MSB first, in order to bring the
comparator back into a balanced condition.
The AD7623 can be operated from a single 2.5 V supply and
be interfaced to either 5 V, 3.3 V, or 2.5 V digital logic. It
is housed in 48-lead LQFP or tiny LFCSP packages that
combine space savings with flexibility, allowing the AD7623
to be configured as either a serial or parallel interface. The
AD7623 is pin-to-pin-compatible with, and a speed upgrade
of, the AD7677.
CONVERTER OPERATION
After the completion of this process, the control logic generates
the ADC output code and brings BUSY output low.
The AD7623 is a successive approximation ADC based on a
charge redistribution DAC. Figure 21 shows the simplified
schematic of the ADC. The capacitive DAC consists of two
identical arrays of 16 binary weighted capacitors, which are
connected to the two comparator inputs.
The AD7623 automatically powers down circuits after
conversion, making the AD7623 ideal for battery-powered
applications.
Rev. 0 | Page 15 of 28
AD7623
TRANSFER FUNCTIONS
Table 7. Output Codes and Ideal Input Voltages
Digital Output Code
2C
Using the OB/ digital input, the AD7623 offers two output
codings: straight binary and twos complement. The LSB size
with VREF = 2.048 V is 2 × VREF/65536, which is 62.5 μV. Refer to
Figure 22 and Table 7 for the ideal transfer characteristic.
Analog Input
VREF = 2.048 V Binary
Straight
Twos
Complement
Description
FSR −1 LSB
FSR − 2 LSB
Midscale + 1 LSB
Midscale
+2.047938 V
+2.047875 V
+62.5 μV
0 V
0xFFFF1
0xFFFE
0x8001
0x8000
0x7FFF
0x0001
0x00002
0x7FFF1
0x7FFE
0x0001
0x0000
0xFFFF
0x8001
0x80002
111...111
111...110
111...101
Midscale − 1 LSB
−FSR + 1 LSB
−FSR
−62.5 μV
−2.047938 V
−2.048 V
1 This is also the code for overrange analog input (VIN+ − VIN− above
VREF − VREFGND).
2 This is also the code for underrange analog input (VIN+ − VIN− below
−VREF + VREFGND).
000...010
000...001
000...000
–FSR+1 LSB
+FSR–1 LSB
+FSR–1.5 LSB
ANALOG INPUT
–FSR
–FSR+0.5 LSB
Figure 22. ADC Ideal Transfer Function
DIGITAL
SUPPLY (2.5V)
NOTE 5
10Ω
DIGITAL
INTERFACE
SUPPLY
ANALOG
SUPPLY (2.5V)
(2.5V OR 3.3V)
100nF
10μF
10μF
10μF
100nF
100nF
AVDD AGND DGND
REF
DVDD
OVDD
OGND
SERIAL
PORT
NOTE 3
SCLK
C
10μF
REF
REFBUFIN
REFGND
100nF
SDOUT
NOTE 4
BUSY
NOTE 7
NOTE 2
MICROCONVERTER/
MICROPROCESSOR/
DSP
50Ω
10Ω
D
CNVST
U1
IN+
50pF
ANALOG
INPUT +
AD7623
C
1nF
C
OB/2C
SER/PAR
CS
NOTE 1
OVDD
NOTE 2
U2
RD
10Ω
CLOCK
IN–
ANALOG
INPUT –
NOTE 3
C
C
1nF
NOTE 1
50pF
PDREF PDBUF
PD
RESET
10kΩ
NOTE 6
1. SEE ANALOG INPUT SECTION.
2. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
3. THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE. SEE VOLTAGE REFERENCE INPUT SECTION.
4. A 10μF CERAMIC CAPACITOR (X5R, 1206 SIZE) IS RECOMMENDED (FOR EXAMPLE, PANASONIC ECJ3YB0J106M).
SEE VOLTAGE REFERENCE INPUT SECTION.
5. OPTION, SEE POWER SUPPLY SECTION.
6. OPTION, SEE POWER-UP SECTION.
7. OPTIONAL LOW JITTER CNVST, SEE CONVERSION CONTROL SECTION.
Figure 23. Typical Connection Diagram
Rev. 0 | Page 16 of 28
AD7623
comprised of some serial resistors and the on resistance of the
switches. CIN is typically 12 pF and is primarily the ADC
sampling capacitor. During the conversion phase, when the
switches are opened, the input impedance is limited to CPIN. RIN
and CIN make a one-pole, low-pass filter that has a typical −3 dB
cutoff frequency of 50 MHz, thereby reducing an undesirable
aliasing effect while limiting noise from the inputs.
TYPICAL CONNECTION DIAGRAM
Figure 23 shows a typical connection diagram for the AD7623.
Different circuitry from that shown in this diagram are optional
and are discussed in the Analog Inputs section.
ANALOG INPUTS
Figure 24 shows an equivalent circuit of the input structure of
the AD7623.
Since the input impedance of the AD7623 is very high, the
AD7623 can be directly driven by a low impedance source
without gain error. To further improve the noise filtering
achieved by the AD7623 analog input circuit, an external,
one-pole RC filter between the amplifier’s outputs and the ADC
analog inputs can be used, as shown in Figure 23. However,
large source impedances significantly affect the ac performance,
especially total harmonic distortion (THD). The maximum
source impedance depends on the amount of THD that can be
tolerated. The THD degrades as a function of the source
impedance and the maximum input frequency, as shown in
Figure 26.
The two diodes, D1 and D2, provide ESD protection for the
analog inputs, IN+ and IN−. Care must be taken to ensure that
the analog input signal never exceeds the supply rails by more
than 0.3 V, because this causes the diodes to become forward-
biased and to start conducting current. These diodes can handle
a forward-biased current of 100 mA maximum. For instance,
these conditions could eventually occur when the input buffer’s
U1 or U2 supplies are different from AVDD. In such a case, an
input buffer with a short-circuit current limitation can be used
to protect the part.
AVDD
–60
D
C
1
2
R
IN
IN
PDBUF = PDREF = LOW
IN+ OR IN–
AGND
–65
–70
C
D
PIN
R
= 500Ω
S
–75
–80
Figure 24. AD7623 Simplified Analog Input
The analog inputs of the AD7623 are a true differential
structure. By using this differential input, small signals common
to both inputs are rejected, as shown in Figure 25, representing
the typical CMRR over frequency with internal and external
references.
–85
R
= 100Ω
S
–90
R
= 50Ω
S
–95
R
= 10Ω
S
–100
75
70
65
1
10
100
1k
INPUT FREQUENCY (kHz)
Figure 26. THD vs. Analog Input Frequency and Source Resistance
DRIVER AMPLIFIER CHOICE
Although the AD7623 is easy to drive, the driver amplifier must
meet the following requirements:
EXT REF
60
•
Together, the driver amplifier and the AD7623 analog
input circuit must be able to settle for a full-scale step of
the capacitor array at a 16-bit level (0.0015%). In the
amplifier data sheet, settling at 0.1% to 0.01% is more
commonly specified. This could differ significantly from
the settling time at a 16-bit level and should be verified
prior to driver selection. The AD8021 op amp, which
combines ultralow noise and high gain bandwidth, meets
this settling time requirement even when used with gains
up to 13.
INT REF
55
50
45
1
10
100
1000
10000
FREQUENCY (kHz)
Figure 25. Analog Input CMRR vs. Frequency
During the acquisition phase for ac signals, the impedance of
the analog inputs, IN+ and IN−, can be modeled as a parallel
combination of Capacitor CPIN and the network formed by the
series connection of RIN and CIN. CPIN is primarily the pin
capacitance. RIN is typically 350 Ω and is a lumped component
•
The noise generated by the driver amplifier needs to be
kept as low as possible to preserve the SNR and transition
noise performance of the AD7623. The noise coming from
the driver is filtered by the AD7623 analog input circuit
Rev. 0 | Page 17 of 28
AD7623
one-pole, low-pass filter made by RIN and CIN or by the
external filter, if one is used. The SNR degradation due to
the amplifier is
U1
AD8021
10pF
ANALOG INPUT
(UNIPOLAR 0V TO 2.048V)
⎛
⎜
⎞
⎟
53
590Ω
590Ω
SNRLOSS = 20log
10Ω
1nF
⎜
⎜
⎟
⎟
2
IN+
2809 + πf−3dB
(
NeN
)
⎝
⎠
AD7623
where:
–3dB is the input bandwidth of the AD7623 (50 MHz) or the
cutoff frequency of the input filter (16 MHz), if one is used.
10Ω
1nF
U2
IN–
1kΩ
REF
f
AD8021
10pF
1kΩ
100nF
10μF
N is the noise factor of the amplifier (+1 in buffer
configuration).
eN is the equivalent input voltage noise density of the op
Figure 27. Single-Ended-to-Differential Driver Circuit
(Internal Reference Buffer Used)
amp, in nV/√Hz.
VOLTAGE REFERENCE INPUT
For instance, a driver with an equivalent input noise
density of 2.1 nV/√Hz, like the AD8021 with a noise gain
of +1 when configured as a buffer, degrades the SNR by
only 0.33 dB when using the RC filter in Figure 23, and by
1 dB without using it.
The AD7623 allows the choice of either a very low temperature
drift internal voltage reference or an external reference.
Unlike many ADCs with internal references, the internal
reference of the AD7623 provides excellent performance and
can be used in almost all applications.
•
The driver needs to have a THD performance suitable to
that of the AD7623. Figure 13 gives the THD vs. frequency
that the driver should exceed.
Internal Reference
(PDBUF = Low, PDREF = Low)
To use the internal reference, the PDREF and PDBUF inputs
must be low. This produces a 1.2 V band gap output on
REFBUFIN which, amplified by the internal buffer, results in a
2.048 V reference on the REF pin.
The AD8021 meets these requirements and is appropriate for
almost all applications. The AD8021 needs a 10 pF external
compensation capacitor that should have good linearity as an
NPO ceramic or mica type. Moreover, the use of a noninverting
+1 gain arrangement is recommended and helps to obtain the
best signal-to-noise ratio.
The internal reference is temperature-compensated to
2.048 V 10 mV. The reference is trimmed to provide a typical
drift of 7 ppm/°C. This typical drift characteristic is shown
in Figure 7.
The AD8022 can also be used when a dual version is needed
and a gain of 1 is present. The AD829 is an alternative in
applications where high frequency (above 100 kHz) performance
is not required.
The output resistance of the REFBUFIN is 6.33 kΩ (minimum)
when the internal reference is enabled. It is necessary to
decouple this with a ceramic capacitor greater than 100 nF.
Thus, the capacitor provides an RC filter for noise reduction.
In applications with a gain of 1, an 82 pF compensation
capacitor is required. The AD8610 is an option when low bias
current is needed in low frequency applications.
Since the output impedance of REFBUFIN is typically 6.33 kΩ,
relative humidity (among other industrial contaminates) can
directly affect the drift characteristics of the reference. Typically,
a guard ring is used to reduce the effects of drift under such
circumstances. However, since the AD7623 has a fine lead pitch,
guarding this node is not practical. Therefore, in these
industrial and other types of applications, it is recommended to
use a conformal coating, such as Dow Corning 1-2577 or
Humiseal 1B73.
Single-to-Differential Driver
For applications using unipolar analog signals, a single-ended-
to-differential driver, as shown in Figure 27, allows for a
differential input into the part. This configuration, when
provided an input signal of 0 to VREF, produces a differential
VREF with midscale at VREF/2. The one-pole filter using R = 10 Ω
and C = 1 nF provides a corner frequency of 16 MHz.
If the application can tolerate more noise, the AD8139 differen-
tial driver can be used.
External 1.2 V Reference and Internal Buffer
(PDREF = High, PBBUF = Low)
To use an external reference with the internal buffer, PDREF
should be high and PDBUF should be low. This powers down
the internal reference and allows the 1.2 V reference to be
applied to REFBUFIN.
Rev. 0 | Page 18 of 28
AD7623
External Reference (PDBUF = High, PRBUF = High)
Temperature Sensor
To use an external reference directly on the REF pin, PDREF
and PDBUF should both be high. PDREF and PDBUF power
down the internal reference and the internal reference buffer,
respectively.
The TEMP pin measures the temperature of the AD7623. To
improve the calibration accuracy over the temperature range,
the output of the TEMP pin is applied to one of the inputs of
the analog switch (such as ADG779), and the ADC itself is used
to measure its own temperature. This configuration is shown
in Figure 28.
For improved drift performance, an external reference, such as
the AD780 or ADR431, can be used. The advantages of directly
using the external voltage reference are:
TEMP
ADG779
•
SNR and dynamic range improvement (about 1.7 dB)
resulting from the use of a reference voltage very close to
the supply (2.5 V) instead of a typical 2.048 V reference
when the internal reference is used. This is calculated by
TEMPERATURE
IN+
ANALOG INPUT
(UNIPOLAR)
SENSOR
AD7623
C
AD8021
C
Figure 28. Use of the Temperature Sensor
2.50
2.048
⎛
⎜
⎝
⎞
⎟
⎠
SNR = 20 log
POWER SUPPLY
•
Power savings when the internal reference is powered
down (PBREF = PDBUF = high).
The AD7623 uses three sets of power supply pins: an analog
2.5 V supply AVDD, a digital 2.5 V core supply DVDD, and a
digital input/output interface supply OVDD. The OVDD supply
allows direct interface with any logic working between 2.3 V
and 5.25 V. To reduce the number of supplies needed, the digital
core (DVDD) can be supplied through a simple RC filter from
the analog supply, as shown in Figure 23.
Reference Decoupling
Whether using an internal or external reference, the AD7623
voltage reference input (REF) has a dynamic input impedance;
therefore, it should be driven by a low impedance source with
efficient decoupling between the REF and REFGND inputs.
This decoupling depends on the choice of the voltage reference,
but usually consists of a low ESR capacitor connected to REF
and REFGND with minimum parasitic inductance. A 10 μF
(X5R, 1206 size) ceramic chip capacitor (or 47 μF tantalum
capacitor) is appropriate when using either the internal
reference or one of these recommended reference voltages:
Power Sequencing
The AD7623 is independent of power supply sequencing once
OVDD does not exceed DVDD by more than 0.3 V until
DVDD = 2.3 V during any time; for instance, at power-up or
power-down (see the Absolute Maximum Ratings section).
Additionally, it is very insensitive to power supply variations
over a wide frequency range as shown in Figure 29.
•
•
•
The low noise, low temperature drift ADR431 and AD780
The low power ADR291
75
70
65
The low cost AD1582
The placement of the reference decoupling is also important to
the performance of the AD7623. The decoupling capacitor
should be mounted on the same side as the ADC right at the
REF pin with a thick PCB trace. The REFGND should also
connect to the reference decoupling capacitor with the shortest
distance.
EXT REF
60
INT REF
55
For applications that use multiple AD7623 devices, it is more
effective to use the internal reference buffer to buffer the
reference voltage.
50
45
1
10
100
1k
10k
FREQUENCY (kHz)
The voltage reference temperature coefficient (TC) directly
impacts full scale; therefore, in applications where full-scale
accuracy matters, care must be taken with the TC. For instance,
a 15 ppm/°C TC of the reference changes full-scale by 1 LSB/°C.
Figure 29. PSRR vs. Frequency
Rev. 0 | Page 19 of 28
AD7623
CONVERSION CONTROL
Power-Up
CNVST
The AD7623 is controlled by the
input. A falling edge
At power-up, or returning to operational mode from the power-
down mode (PD = high), the AD7623 engages an initialization
process. During this time, the first 128 conversions should be
ignored or the RESET input could be pulsed to engage a faster
initialization process. Refer to the Digital Interface section for
RESET and timing details.
CNVST
on
is all that is necessary to initiate a conversion.
Detailed timing diagrams of the conversion process are shown
in Figure 31. Once initiated, it cannot be restarted or aborted,
even by the power-down input, PD, until the conversion is
CNVST
CS
complete. The
RD
signal operates independently of
and
signals.
A simple power-on reset circuit, as shown in Figure 23, can be
used to minimize the digital interface. As OVDD powers up, the
capacitor is shorted and brings RESET high; it is then charged,
returning RESET to low. However, this circuit only works when
powering up the AD7623 because the power-down mode
(PD = high) does not power down any of the supplies. As a
result, RESET is low.
t2
t1
CNVST
BUSY
t4
t3
t5
t6
POWER DISSIPATION VS. THROUGHPUT
The AD7623 automatically reduces its power consumption at
the end of each conversion phase. During the acquisition phase,
the operating currents are very low, which allows a significant
power savings when the conversion rate is reduced (see Figure 30).
This feature makes the AD7623 ideal for very low power,
battery-operated applications.
MODE
ACQUIRE
CONVERT
t7
ACQUIRE
t8
CONVERT
Figure 31. Basic Conversion Timing
CNVST
low time, t1, or until the end
For optimal performance, the rising edge of
occur after the maximum
of conversion.
should not
CNVST
It should be noted that the digital interface remains active even
during the acquisition phase. To reduce the operating digital
supply currents even further, drive the digital inputs close to the
power rails (that is, OVDD and OGND).
CNVST
Although
is a digital signal, it should be designed with
special care with fast, clean edges, and levels with minimum
overshoot, undershoot, or ringing.
100k
PDREF = PDBUF = HIGH
CNVST
The
trace should be shielded with ground, and a low
value (such as 50 Ω) serial resistor termination should be added
close to the output of the component that drives this line. Also,
a 60 pF capacitor is recommended to further reduce the effects
of overshoot and undershoot, as shown in Figure 23.
10k
1k
CNVST
For applications where SNR is critical, the
have very low jitter. This can be achieved by using a dedicated
CNVST CNVST
with a
signal should
oscillator for
generation, or by clocking
high frequency, low jitter clock, as shown in Figure 23.
100
100
1k
10k
100k
1M
10M
SAMPLING RATE (SPS)
Figure 30. Power Dissipation vs. Sample Rate
Rev. 0 | Page 20 of 28
AD7623
INTERFACES
DIGITAL INTERFACE
PARALLEL INTERFACE
The AD7623 has a versatile digital interface that can be set up
as either a serial or parallel interface with the host system. The
serial interface is multiplexed on the parallel data bus. The
AD7623 digital interface also accommodates 2.5 V, 3.3 V, or 5 V
logic with either OVDD at 2.5 V or 3.3 V. OVDD defines the
logic high output voltage. In most applications, the OVDD
supply pin of the AD7623 is connected to the host system
interface 2.5 V or 3.3 V digital supply. Finally, by using the
The AD7623 is configured to use the parallel interface when
PAR
SER/
is held low.
Master Parallel Interface
CS
RD
low, thus
Data can be continuously read by tying
and
requiring minimal microprocessor connections. However, in
this mode, the data bus is always driven and cannot be used in
shared bus applications (unless the device is held in RESET).
Figure 33 details the timing for this mode.
2C
OB/ input pin, both twos complement or straight binary
coding can be used.
CS = RD = 0
t1
CS
RD
, control the interface. When at least
The two signals,
one of these signals is high, the interface outputs are in high
CS
and
CNVST
impedance. Usually,
multicircuit applications and is held low in a single AD7623
RD
allows the selection of each AD7623 in
t10
BUSY
t4
design.
is generally used to enable the conversion result on
t3
t11
the data bus.
DATA
BUS
PREVIOUS CONVERSION DATA
NEW DATA
RESET
Figure 33. Master Parallel Data Timing for Reading (Continuous Read)
The RESET input is used to reset the AD7623 and generate a
fast initialization. A rising edge on RESET aborts the current
conversion (if any) and tristates the data bus. The falling edge of
RESET clears the data bus and engages the initialization process
indicated by pulsing BUSY high. Conversions can take place
after the falling edge of BUSY. Refer to Figure 32 for the RESET
timing details.
Slave Parallel Interface
In slave parallel reading mode, the data can be read either after
each conversion, which is during the next acquisition phase, or
during the following conversion, as shown in Figure 34 and
Figure 35, respectively. When the data is read during the
conversion, it is recommended that it is read-only during the
first half of the conversion phase. This avoids any potential
feedthrough between voltage transients on the digital interface
and the most critical analog conversion circuitry.
t9
RESET
CNVST
DATA
BUSY
CS
RD
t38
t39
t8
Figure 32. RESET Timing
BUSY
DATA
BUS
CURRENT
CONVERSION
t12
t13
Figure 34. Slave Parallel Data Timing for Reading (Read After Convert)
Rev. 0 | Page 21 of 28
AD7623
CS = 0
SERIAL INTERFACE
CNVST,
RD
t1
The AD7623 is configured to use the serial interface when
PAR
SER/
is held high. The AD7623 outputs 16 bits of data,
MSB first, on the SDOUT pin. This data is synchronized with
the 16 clock pulses provided on the SCLK pin. The output data
is valid on both the rising and falling edge of the data clock.
BUSY
t4
t3
MASTER SERIAL INTERFACE
Internal Clock
DATA
BUS
PREVIOUS
CONVERSION
The AD7623 is configured to generate and provide the serial
t12
t13
INT
data clock SCLK when the EXT/
pin is held low. The
Figure 35. Slave Parallel Data Timing for Reading (Read During Convert)
AD7623 also generates a SYNC signal to indicate to the host
when the serial data is valid. The serial clock SCLK and the
SYNC signal can be inverted, if desired. Depending on the read
during convert input, RDC/SDIN, the data can be read after
each conversion or during the following conversion. Figure 37
and Figure 38 show detailed timing diagrams of these two
modes.
8-Bit Interface (Master or Slave)
The BYTESWAP pin allows a glueless interface to an 8-bit bus.
As shown in Figure 36, when BYTESWAP is low, the LSB byte is
output on D[7:0] and the MSB is output on D[15:8]. When
BYTESWAP is high, the LSB and MSB bytes are swapped, and
the LSB is output on D[15:8] and the MSB is output on D[7:0].
By connecting BYTESWAP to an address line, the 16-bit data
can be read in two bytes on either D[15:8] or D[7:0]. This
interface can be used in both master and slave parallel reading
modes.
Usually, because the AD7623 is used with a fast throughput, the
master read during conversion mode is the most recommended
serial mode. In this mode, the serial clock and data toggle at
appropriate instants, minimizing potential feedthrough between
digital activity and critical conversion decisions. In this mode,
the SCLK period changes since the LSBs require more time to
settle and the SCLK is derived from the SAR conversion cycle.
CS
RD
In read after conversion mode, unlike other modes, the BUSY
signal returns low after the 16 data bits are pulsed out and not at
the end of the conversion phase, resulting in a longer BUSY
width. As a result, the maximum throughput cannot be
achieved in this mode.
BYTESWAP
HI-Z
HI-Z
HI-Z
HI-Z
PINS D[15:8]
PINS D[7:0]
HIGH BYTE
LOW BYTE
t12
LOW BYTE
t12
t13
HIGH BYTE
Figure 36. 8-Bit and 16-Bit Parallel Interface
Rev. 0 | Page 22 of 28
AD7623
RDC/SDIN = 0
INVSCLK = INVSYNC = 0
EXT/INT = 0
CS, RD
CNVST
t3
t28
BUSY
SYNC
t30
t29
t25
t18
t19
t14
t24
t20
t21
2
t26
1
3
14
15
16
SCLK
t15
t27
SDOUT
D15
D14
t23
D2
D1
D0
X
t16
t22
Figure 37. Master Serial Data Timing for Reading (Read After Convert)
EXT/INT = 0
RDC/SDIN = 1
INVSCLK = INVSYNC = 0
CS, RD
CNVST
t1
t3
BUSY
SYNC
t17
t25
t19
t20 t21
t14
t24
t26
t15
SCLK
1
2
3
14
15
16
t18
t27
SDOUT
X
D15
D14
t23
D2
D1
D0
t16
t22
Figure 38. Master Serial Data Timing for Reading (Read Previous Conversion During Convert)
Rev. 0 | Page 23 of 28
AD7623
An example of the concatenation of two devices is shown in
Figure 39. Simultaneous sampling is possible by using a
SLAVE SERIAL INTERFACE
External Clock
CNVST
common
signal. It should be noted that the RDC/SDIN
The AD7623 is configured to accept an externally supplied
input is latched on the edge of SCLK opposite to the one used to
shift out the data on SDOUT. Hence, the MSB of the upstream
converter just follows the LSB of the downstream converter on
the next SCLK cycle.
INT
serial data clock on the SCLK pin when the EXT/
held high. In this mode, several methods can be used to read
CS CS
pin is
the data. The external serial clock is gated by . When
and
are both low, the data can be read after each conversion or
RD
BUSY
OUT
during the following conversion. The external clock can be
either a continuous or a discontinuous clock. A discontinuous
clock can be either normally high or normally low when
inactive. Figure 40 and Figure 41 show the detailed timing
diagrams of these methods.
BUSY
BUSY
AD7623
AD7623
#2
#1
(UPSTREAM)
(DOWNSTREAM)
DATA
OUT
RDC/SDIN
SDOUT
RDC/SDIN
SDOUT
While the AD7623 is performing a bit decision, it is important
that voltage transients be avoided on digital input/output pins,
or degradation of the conversion result could occur. This is
particularly important during the second half of the conversion
phase because the AD7623 provides error correction circuitry
that can correct for an improper bit decision made during the
first half of the conversion phase. For this reason, it is recom-
mended that when an external clock is being provided, it is a
discontinuous clock that is toggling only when BUSY is low or,
more importantly, that it does not transition during the latter
half of BUSY high.
CNVST
CS
CNVST
CS
SCLK
SCLK
SCLK IN
CS IN
CNVST IN
Figure 39. Two AD7623 Devices in a Daisy-Chain Configuration
External Clock Data Read During Previous Conversion
Figure 41 shows the detailed timing diagrams of this method.
External Discontinuous Clock Data Read After
Conversion
CS
RD
During a conversion, while both
and
are low, the result
of the previous conversion can be read. The data is shifted out,
MSB first, with 16 clock pulses, and is valid on both the rising
and falling edge of the clock. The 16 bits have to be read before
the current conversion is complete; otherwise, RDERROR is
pulsed high and can be used to interrupt the host interface to
prevent incomplete data reading. There is no daisy-chain
feature in this mode, and RDC/SDIN input should always be
tied either high or low.
Though the maximum throughput cannot be achieved using
this mode, it is the most recommended of the serial slave
modes. Figure 40 shows the detailed timing diagrams of this
method. After a conversion is complete, indicated by BUSY
returning low, the conversion result can be read while both
CS
and
are low. Data is shifted out MSB first with 16 clock
RD
pulses and is valid on the rising and falling edges of the clock.
One advantage of this method is that conversion performance
is not degraded because there are no voltage transients on the
digital interface during the conversion process. Another
advantage is the ability to read the data at any speed up to
80 MHz, which accommodates both the slow digital host
interface and the fastest serial reading.
To reduce performance degradation due to digital activity, a fast
discontinuous clock of at least 40 MHz is recommended to
ensure that all the bits are read during the first half of the SAR
conversion phase.
It is also possible to begin to read data after conversion and
continue to read the last bits after a new conversion has been
initiated.
Finally, in this mode only, the AD7623 provides a daisy-chain
feature using the RDC/SDIN pin for cascading multiple con-
verters together. This feature is useful for reducing component
count and wiring connections when desired, as, for instance, in
isolated multiconverter applications.
Rev. 0 | Page 24 of 28
AD7623
RD = 0
EXT/INT = 1
INVSCLK = 0
CS
BUSY
SCLK
t35
t36 t37
1
2
3
14
15
16
17
18
t31
t32
X
D15
t34
D14
D13
X13
D1
X1
X15
Y15
X14
Y14
SDOUT
SDIN
D0
X0
t16
X15
X14
t33
Figure 40. Slave Serial Data Timing for Reading (Read After Convert)
t31
RD = 0
EXT/INT = 1
INVSCLK = 0
CS
t3
CNVST
BUSY
t35
t36
t37
SCLK
14
4
15
16
2
3
1
t32
SDOUT
X
D1
D15
D14
D13
D2
D0
t16
Figure 41. Slave Serial Data Timing for Reading (Read Previous Conversion During Convert)
Rev. 0 | Page 25 of 28
AD7623
The reading process can be initiated in response to the end-of-
conversion signal (BUSY going low) using an interrupt line of
the DSP. The serial peripheral interface (SPI) on the ADSP-219x
is configured for master mode (MSTR) = 1, clock polarity bit
(CPOL) = 0, clock phase bit (CPHA) = 1, and SPI interrupt
enable (TIMOD) = 00 by writing to the SPI control register
(SPICLTx).
MICROPROCESSOR INTERFACING
The AD7623 is ideally suited for traditional dc measurement
applications supporting a microprocessor, and ac signal
processing applications interfacing to a digital signal processor.
The AD7623 is designed to interface with a parallel 8-bit or
16-bit wide interface, or with a general-purpose serial port or
I/O ports on a microcontroller. A variety of external buffers can
be used with the AD7623 to prevent digital noise from coupling
into the ADC. The SPI Interface (ADSP-219x) section shows
the use of the AD7623 with an ADSP-219x SPI-equipped DSP.
It should be noted that to meet all timing requirements, the SPI
clock should be limited to 17 Mb/s allowing it to read an ADC
result in less than 1 μs. When a higher sampling rate is desired,
use one of the parallel interface modes.
SPI Interface (ADSP-219x)
DVDD
Figure 42 shows an interface diagram between the AD7623 and
an SPI-equipped DSP, ADSP-219x. To accommodate the slower
speed of the DSP, the AD7623 acts as a slave device, and data
must be read after conversion. This mode also allows the daisy-
chain feature. The convert command could be initiated in
response to an internal timer interrupt.
AD7623*
ADSP-219x*
SER/PAR
BUSY
CS
PFx
EXT/INT
SPIxSEL (PFx)
MISOx
SDOUT
SCLK
CNVST
RD
SCKx
PFx OR TFSx
INVSCLK
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 42. Interfacing the AD7623 to SPI Interface
Rev. 0 | Page 26 of 28
AD7623
APPLICATION
LAYOUT
The DVDD supply of the AD7623 can be either a separate
supply or come from the analog supply, AVDD, or from the
digital interface supply, OVDD. When the system digital supply
is noisy, or fast switching digital signals are present, and no
separate supply is available, it is recommended to connect the
DVDD digital supply to the analog supply AVDD through an
RC filter, and to connect the system supply to the interface
digital supply OVDD and the remaining digital circuitry. Refer
to Figure 23 for an example of this configuration. When DVDD
is powered from the system supply, it is useful to insert a bead
to further reduce high frequency spikes.
While the AD7623 has very good immunity to noise on the
power supplies, exercise care with the grounding layout. To
facilitate the use of ground planes that can be easily separated,
design the printed circuit board that houses the AD7623 so that
the analog and digital sections are separated and confined to
certain areas of the board. Digital and analog ground planes
should be joined in only one place, preferably underneath the
AD7623, or as close as possible to the AD7623. If the AD7623 is
in a system where multiple devices require analog-to-digital
ground connections, the connections should still be made at
one point only, a star ground point, established as close as
possible to the AD7623.
The AD7623 has four different ground pins: REFGND, AGND,
DGND, and OGND. REFGND senses the reference voltage and,
because it carries pulsed currents, should be a low impedance
return to the reference. AGND is the ground to which most
internal ADC analog signals are referenced; it must be
connected with the least resistance to the analog ground plane.
DGND must be tied to the analog or digital ground plane
depending on the configuration. OGND is connected to the
digital system ground.
To prevent coupling noise onto the die, avoid radiating noise,
and to reduce feedthrough:
• Do not run digital lines under the device.
• Do run the analog ground plane under the AD7623.
CNVST
• Do shield fast switching signals, like
or clocks, with
digital ground to avoid radiating noise to other sections of
the board, and never run them near analog signal paths.
The layout of the decoupling of the reference voltage is
important. To minimize parasitic inductances, place the
decoupling capacitor close to the ADC and connect it with
short, thick traces.
• Avoid crossover of digital and analog signals.
• Run traces on different but close layers of the board, at right
angles to each other, to reduce the effect of feedthrough
through the board.
EVALUATING THE AD7623 PERFORMANCE
A recommended layout for the AD7623 is outlined in the
documentation of the EVAL-AD7623CB evaluation board
for the AD7623. The evaluation board package includes a fully
assembled and tested evaluation board, documentation, and
software for controlling the board from a PC via the
EVAL-CONTROL BRD3.
The power supply lines to the AD7623 should use as large a
trace as possible to provide low impedance paths and reduce the
effect of glitches on the power supply lines. Good decoupling is
also important to lower the impedance of the supplies presented
to the AD7623, and to reduce the magnitude of the supply
spikes. Decoupling ceramic capacitors, typically 100 nF, should
be placed on each of the power supplies pins, AVDD, DVDD,
and OVDD. The capacitors should be placed close to, and
ideally right up against, these pins and their corresponding
ground pins. Additionally, low ESR 10 μF capacitors should be
located in the vicinity of the ADC to further reduce low
frequency ripple.
Rev. 0 | Page 27 of 28
AD7623
OUTLINE DIMENSIONS
0.75
0.60
0.45
9.00
BSC SQ
1.60
MAX
37
48
1
36
PIN 1
7.00
BSC SQ
TOP VIEW
(PINS DOWN)
1.45
1.40
1.35
0.20
0.09
7°
3.5°
0°
25
12
0.15
0.05
13
24
SEATING
PLANE
0.08 MAX
COPLANARITY
0.27
0.22
0.17
VIEW A
0.50
BSC
LEAD PITCH
VIEW A
ROTATED 90° CCW
COMPLIANT TO JEDEC STANDARDS MS-026-BBC
Figure 43. 48-Lead Low Profile Quad Flat Package [LQFP]
(ST-48)
Dimensions shown in millimeters
0.30
7.00
BSC SQ
0.23
0.18
0.60 MAX
0.60 MAX
PIN 1
INDICATOR
37
36
48
1
PIN 1
INDICATOR
EXPOSED
5.25
5.10 SQ
4.95
TOP
VIEW
6.75
BSC SQ
(BOTTOM VIEW)
0.50
0.40
0.30
25
24
12
13
0.25 MIN
5.50
REF
PADDLE CONNECTED TO GND.
THIS CONNECTION IS NOT
REQUIRED TO MEET THE
0.80 MAX
0.65 TYP
1.00
0.85
0.80
12° MAX
0.05 MAX
0.02 NOM
ELECTRICAL PERFORMANCES
COPLANARITY
0.08
0.50 BSC
0.20 REF
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2
Figure 44. 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
7 mm × 7 mm Body, Very Thin Quad
(CP-48-1)
Dimensions shown in millimeters
ORDERING GUIDE
Model
AD7623ACP
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
Package Option
CP-48-1
CP-48-1
CP-48-1
CP-48-1
ST-48
ST-48
ST-48
ST-48
48-Lead Lead Frame Chip Scale (LFCSP_VQ)
48-Lead Lead Frame Chip Scale (LFCSP_VQ)
48-Lead Lead Frame Chip Scale (LFCSP_VQ)
48-Lead Lead Frame Chip Scale (LFCSP_VQ)
48-Lead Low Profile Quad Flatpack (LQFP)
48-Lead Low Profile Quad Flatpack (LQFP)
48-Lead Low Profile Quad Flatpack (LQFP)
48-Lead Low Profile Quad Flatpack (LQFP)
Evaluation Board
AD7623ACPRL
AD7623ACPZ1
AD7623ACPZRL1
AD7623AST
AD7623ASTRL
AD7623ASTZ1
AD7623ASTZRL1
EVAL-AD7623CB2
EVAL-CONTROL BRD33
Controller Board
1 Z = Pb-free part.
2 This board can be used as a standalone evaluation board or in conjunction with the EVAL-CONTROL BRD3 for evaluation/demonstration purposes.
3 This board allows a PC to control and communicate with all Analog Devices, Inc. evaluation boards ending in the CB designator.
©
2005 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05574–0–7/05(0)
Rev. 0 | Page 28 of 28
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