AD7652ACPRL [ADI]
16-Bit 500 kSPS PulSARTM Unipolar ADC with Reference; 16位500 kSPS的PulSARTM单极性ADC与参考
| 型号： | AD7652ACPRL |
| 厂家： | 
ADI |
| 描述： | 16-Bit 500 kSPS PulSARTM Unipolar ADC with Reference |
| 文件： | 总28页 (文件大小：804K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
16-Bit 500 kSPS PulSARTM
Unipolar ADC with Reference
AD7652
FEATURES
FUNCTIONAL BLOCK DIAGRAM
REFBUFIN
Throughput: 500 kSPS
REF REFGND
DVDD DGND
16-bit resolution
Analog input voltage range: 0 V to 2.5 V
No pipeline delay
OVDD
OGND
AGND
AVDD
AD7652
SERIAL
PORT
REF
Parallel and serial 5 V/3 V interface
16
IN
SWITCHED
CAP DAC
DATA[15:0]
BUSY
SPI®/QSPITM/MICROWIRETM/DSP compatible
Single 5 V supply operation
Power dissipation
65 mW typ, 130 µW @ 1 kSPS without REF
80 mW typ with REF
INGND
PARALLEL
INTERFACE
PDREF
PDBUF
RD
CLOCK
CS
PD
CONTROL LOGIC AND
SER/PAR
RESET
CALIBRATION CIRCUITRY
OB/2C
48-lead LQFP and 48-lead LFCSP packages
Pin-to-pin compatible with PulSAR ADCs
BYTESWAP
CNVST
02965-0-001
Figure 1. Functional Block Diagram
APPLICATIONS
Data acquisition
Instrumentation
Table 1. PulSAR Selection
800–
1000
Digital signal processing
Spectrum analysis
Medical instruments
Battery-powered systems
Process control
Type/kSPS
100–250
500–570
Pseudo-
Differential
AD7651
AD7650/AD7652 AD7653
AD7660/AD7661 AD7664/AD7666 AD7667
True Bipolar
AD7663
AD7675
AD7665
AD7676
AD7671
AD7677
True
Differential
GENERAL DESCRIPTION
18-Bit
AD7678
AD7679
AD7654
AD7655
AD7674
The AD7652 is a 16-bit, 500 kSPS, charge redistribution SAR
analog-to-digital converter that operates from a single 5 V
power supply. The part contains a high speed 16-bit sampling
ADC, an internal conversion clock, internal reference, error
correction circuits, and both serial and parallel system interface
ports.
Multichannel/
Simultaneous
PRODUCT HIGHLIGHTS
1. Fast Throughput.
The AD7652 is a 500 kSPS, charge redistribution, 16-bit
SAR ADC with internal error correction circuitry.
The AD7652 is fabricated using Analog Devices’ high perform-
ance, 0.6 micron CMOS process, with correspondingly low cost,
and is available in a 48-lead LQFP and a tiny 48-lead LFCSP
with operation specified from –40°C to +85°C.
2. Internal Reference.
The AD7652 has an internal reference with a typical
temperature drift of 7 ppm/°C.
3. Single-Supply Operation.
The AD7652 operates from a single 5 V supply. Its power
dissipation decreases with throughput.
4. Serial or Parallel Interface.
Versatile parallel or 2-wire serial interface arrangement is
compatible with both 3 V and 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: 781.326.8703
www.analog.com
© 2003 Analog Devices, Inc. All rights reserved.
AD7652
TABLE OF CONTENTS
Specifications..................................................................................... 3
Timing Specifications....................................................................... 5
Absolute Maximum Ratings............................................................ 7
Pin Configuration and Function Descriptions............................. 8
Definitions of Specifications ......................................................... 11
Typical Performance Characteristics ........................................... 12
Circuit Information........................................................................ 15
Converter Operation.................................................................. 15
Typical Connection Diagram.................................................... 17
Power Dissipation versus Throughput .................................... 19
Conversion Control.................................................................... 19
Digital Interface .......................................................................... 20
Parallel Interface......................................................................... 20
Serial Interface ............................................................................ 20
Master Serial Interface............................................................... 21
Slave Serial Interface .................................................................. 22
Microprocessor Interfacing....................................................... 24
Application Hints............................................................................ 25
Bipolar and Wider Input Ranges.............................................. 25
Layout .......................................................................................... 25
Evaluating the AD7652’s Performance .................................... 25
Outline Dimensions ....................................................................... 26
Ordering Guide........................................................................... 26
REVISION HISTORY
Revision 0, Initial Version.
Rev. 0 | Page 2 of 28
AD7652
SPECIFICATIONS
Table 2. –40°C to +85°C, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise noted
Parameter
Conditions
Min
Typ
Max
Unit
RESOLUTION
16
Bits
ANALOG INPUT
Voltage Range
Operating Input Voltage
VIN – VINGND
VIN
0
–0.1
VREF
+3
V
V
VINGND
–0.1
+0.5
V
Analog Input CMRR
Input Current
fIN = 10 kHz
500 kSPS Throughput
65
6.1
dB
µA
Input Impedance1
THROUGHPUT SPEED
Complete Cycle
2
µs
Throughput Rate
0
500
kSPS
DC ACCURACY
Integral Linearity Error
No Missing Codes
Differential Linearity Error
Transition Noise
Unipolar Zero Error, TMIN to TMAX
Unipolar Zero Error Temperature Drift3
Full-Scale Error, TMIN to TMAX
–6
15
–2
+6
+3
5
LSB2
Bits
LSB
LSB
0.7
3
LSB
0.24
ppm/°C
% of FSR
ppm/°C
LSB
3
REF = 2.5 V
0.12
Full-Scale Error Temperature Drift
Power Supply Sensitivity
AC ACCURACY
0.5
2
AVDD = 5 V 5%
Signal-to-Noise
Spurious Free Dynamic Range
Total Harmonic Distortion
fIN = 100 kHz
fIN = 100 kHz
fIN = 45 kHz
fIN = 100 kHz
86
98
–98
–96
86
dB4
dB
dB
dB
dB
Signal-to-(Noise + Distortion)
fIN = 100 kHz
–60 dB Input, fIN = 100 kHz
30
dB
–3 dB Input Bandwidth
SAMPLING DYNAMICS
Aperture Delay
Aperture Jitter
Transient Response
12
MHz
2
5
ns
ps rms
ns
Full-Scale Step
750
REFERENCE
Internal Reference Voltage
Internal Reference Temperature Drift
Line Regulation
Turn-On Settling Time
Temperature Pin
VREF @ 25°C
–40°C to +85°C
AVDD = 5 V 5%
2.48
2.5
7
24
5
2.52
V
ppm/°C
ppm/V
ms
CREF = 10 µF
Voltage Output @ 25°C
Temperature Sensitivity
Output Resistance
External Reference Voltage Range
External Reference Current Drain
300
1
4.3
2.5
110
mV
mV/°C
kΩ
V
µA
2.3
AVDD – 1.85
500 kSPS Throughput
Rev. 0 | Page 3 of 28
AD7652
Parameter
Conditions
Min
Typ
Max
Unit
DIGITAL INPUTS
Logic Levels
VIL
VIH
IIL
IIH
–0.3
2.0
–1
+0.8
DVDD + 0.3
+1
+1
V
V
µA
µA
–1
DIGITAL OUTPUTS
Data Format5
Pipeline Delay6
VOL
VOH
ISINK = 1.6 mA
ISOURCE = –500 µA
0.4
V
V
OVDD – 0.6
POWER SUPPLIES
Specified Performance
AVDD
DVDD
OVDD
4.75
4.75
2.7
5
5
5.25
5.25
5.257
V
V
V
Operating Current
500 kSPS Throughput
With Reference and Buffer
Reference and Buffer Alone
AVDD8
12.2
3
3.8
102
65
mA
mA
mA
µA
mW
µW
mW
AVDD9
DVDD10
OVDD10
Power Dissipation without REF10
500 kSPS Throughput
1 kSPS Throughput
500 kSPS Throughput
75
130
80
Power Dissipation with REF10
TEMPERATURE RANGE11
Specified Performance
90
TMIN to TMAX
–40
+85
°C
1See Analog Input section.
2LSB means least significant bit. With the 0 V to 2.5 V input range, 1 LSB is 38.15 µV.
3See Definitions of Specifications section. These specifications do not include the error contribution from the external reference.
4All specifications in dB are referred to a full-scale input FS. Tested with an input signal at 0.5 dB below full-scale, unless otherwise specified.
5Parallel or Serial 16-Bit.
6Conversion results are available immediately after completed conversion.
7 The max should be the minimum of 5.25 V and DVDD + 0.3 V.
8 With REF, PDREF and PDBUF are LOW; without REF, PDREF and PDBUF are HIGH.
9 With PDREF, PDBUF LOW and PD HIGH.
10 Tested in Parallel Reading Mode
11Consult factory for extended temperature range.
Rev. 0 | Page 4 of 28
AD7652
TIMING SPECIFICATIONS
Table 3. –40°C to +85°C, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise noted
Parameter
Symbol Min
Typ
Max
Unit
Refer to Figure 26 and Figure 27
Convert Pulsewidth
Time between Conversions
t1
t2
t3
t4
t5
t6
t7
t8
t9
10
2
ns
µs
ns
µs
ns
ns
µs
ns
ns
CNVST
LOW to BUSY HIGH Delay
35
1.25
BUSY HIGH All Modes Except Master Serial Read after Convert
Aperture Delay
End of Conversion to BUSY LOW Delay
Conversion Time
Acquisition Time
RESET Pulsewidth
2
10
1.25
750
10
Refer to Figure 28, Figure 29, and Figure 30 (Parallel Interface Modes)
CNVST
LOW to DATA Valid Delay
t10
t11
t12
t13
1.25
µs
ns
ns
ns
DATA Valid to BUSY LOW Delay
Bus Access Request to DATA Valid
Bus Relinquish Time
12
5
45
15
Refer to Figure 32 and Figure 33 (Master Serial Interface Modes)1
CS
CS
CS
LOW to SYNC Valid Delay
LOW to Internal SCLK Valid Delay
LOW to SDOUT 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
1
CNVST
LOW to SYNC Delay
525
SYNC Asserted to SCLK First Edge Delay
Internal SCLK Period2
Internal SCLK HIGH2
Internal SCLK LOW2
SDOUT Valid Setup Time2
SDOUT Valid Hold Time2
SCLK Last Edge to SYNC Delay2
CS
CS
CS
3
25
12
7
4
2
40
3
HIGH to SYNC HI-Z
10
10
10
HIGH to Internal SCLK HI-Z
HIGH to SDOUT HI-Z
BUSY HIGH in Master Serial Read after Convert2
CNVST
See Table 4
1.25
25
LOW to SYNC Asserted Delay
µs
ns
SYNC Deasserted to BUSY LOW Delay
Refer to Figure 34 and Figure 35 (Slave Serial Interface Modes)1
External SCLK Setup Time
External SCLK Active Edge to SDOUT Delay
SDIN Setup Time
SDIN Hold Time
External SCLK Period
External SCLK HIGH
External SCLK LOW
t31
t32
t33
t34
t35
t36
t37
5
3
5
5
25
10
10
ns
ns
ns
ns
ns
ns
ns
18
1In 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.
2In Serial Master Read during Convert Mode. See Table 4 for serial master read after convert mode.
Rev. 0 | Page 5 of 28
AD7652
Table 4. Serial Clock Timings in Master Read after Convert
DIVSCLK[1]
0
0
1
1
DIVSCLK[0]
Symbol
t18
t19
t19
t20
t21
t22
t23
t24
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
3
17
50
70
22
21
18
4
17
100
140
50
49
18
30
130
3.5
17
25
40
12
7
4
2
200
280
100
99
18
80
3
2
55
2.5
290
5.75
t24
µs
Rev. 0 | Page 6 of 28
AD7652
ABSOLUTE MAXIMUM RATINGS
Table 5. AD7652 Stress Ratings1
I
1.6mA
OL
IN2, TEMP2, REF, REFBUFIN,
INGND, REFGND to AGND
Ground Voltage Differences
AGND, DGND, OGND
Supply Voltages
AVDD + 0.3 V to
AGND – 0.3 V
TO OUTPUT
PIN
1.4V
C
L
0.3 V
60pF*
I
500µA
OH
AVDD, DVDD, OVDD
AVDD to DVDD, AVDD to OVDD
DVDD to OVDD
–0.3 V to +7 V
7 V
–0.3 V to +7 V
–0.3 V to DVDD + 0.3 V
20 ꢀA
*IN SERIAL INTERFACE MODES,THE SYNC, SCLK, AND
SDOUT TIMINGS ARE DEFINEDWITH A MAXIMUM LOAD
C
OF 10pF; OTHERWISE,THE LOAD IS 60pF MAXIMUM.
L
02964-0-006
Digital Inputs
PDREF, PDBUF3
Figure 2. Load Circuit for Digital Interface Timing,
SDOUT, SYNC, SCLK Outputs CL = 10 pF
Internal Power Dissipation4
Internal Power Dissipation5
Junction Teꢀperature
Storage Teꢀperature Range
Lead Teꢀperature Range
(Soldering 10 sec)
700 ꢀW
2.5 W
2V
150°C
0.8V
tDELAY
–65°C to +150°C
300°C
tDELAY
2V
2V
0.8V
0.8V
02965-0-007
1Stresses above those listed under Absolute Maxiꢀuꢀ Ratings ꢀay cause
perꢀanent daꢀage to the device. This is a stress rating only; functional
operation of the device at these or any other conditions above those listed
in the operational sections of this specification is not iꢀplied. Exposure to
absolute ꢀaxiꢀuꢀ rating conditions for extended periods ꢀay affect
device reliability.
Figure 3. Voltage Reference Levels for Timing
2See Analog Input section.
3See Voltage Reference Input Section.
4Specification is for the device in free air:
48-Lead LQFP; θJA = 91°C/W, θJC = 30°C/W
5Specification 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 accuꢀulate on
the huꢀan body and test equipꢀent and can discharge without detection. Although this product features
proprietary ESD protection circuitry, perꢀanent daꢀage ꢀay occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recoꢀꢀended to avoid perforꢀance
degradation or loss of functionality.
Rev. 0 | Page 7 of 28
AD7652
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
48
47 46 45 44 43 42 41 40 39 38 37
1
2
3
4
5
6
7
AGND
AVDD
NC
36
35
34
33
32
31
30
29
AGND
CNVST
PD
RESET
CS
PIN 1
IDENTIFIER
BYTESWAP
OB/2C
NC
NC
AD7652
RD
TOP VIEW
DGND
BUSY
D15
D14
D13
(Not to Scale)
8
9
10
11
12
SER/PAR
D0
D1
28
27
26
25
D2/DIVSCLK0
D3/DIVSCLK1
D12
13 14
15 16 17 18 19 20 21 22 23 24
NC = NO CONNECT
02965-0-002
Figure 4. 48-Lead LQFP (ST-48) and 48-Lead LFCSP (CP-48)
Table 6. Pin Function Descriptions
Pin No. Mnemonic
Type1 Description
1, 36,
AGND
P
Analog Power Ground Pin.
41, 42
2, 44
3, 6,
AVDD
NC
P
Input Analog Power Pin. Nominally 5 V.
No Connect.
7, 40
4
BYTESWAP
OB/2C
DI
Parallel Mode Selection (8-/16-bit). When LOW, the LSB is output on D[7:0] and the MSB is output on
D[15:8]. When HIGH, the LSB is output on D[15:8] and the MSB is output on D[7:0].
Straight Binary/Binary Twos Complement. When OB/2C is 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
DI
8
SER/PAR
D[0:1]
DI
Serial/Parallel Selection Input. When LOW, the parallel port is selected; when HIGH, the serial interface
mode is selected and some bits of the DATA bus are used as a serial port.
Bit 0 and Bit 1 of the Parallel Port Data Output Bus. When SER/PAR is HIGH, these outputs are in high
impedance.
When SER/PAR is LOW, these outputs are used as Bit 2 and Bit 3 of the parallel port data output bus.
When SER/PAR is HIGH, EXT/INT is LOW, and RDC/SDIN is LOW (serial master read after convert), these
inputs, part of the serial port, are used to slow down, if desired, the internal serial clock that clocks the
data output. In other serial modes, these pins are not used.
9, 10
11, 12
DO
DI/O
D[2:3]or
DIVSCLK[0:1]
13
D4 or
DI/O
When SER/PAR is LOW, this output is used as Bit 4 of the parallel port data output bus.
When SER/PAR is HIGH, this input, part of the serial port, is used as a digital select input for choosing
the internal data clock or an external data clock. With EXT/INT tied LOW, the internal clock is selected
on the SCLK output. With EXT/INT set to a logic HIGH, output data is synchronized to an external clock
signal connected to the SCLK input.
INT
EXT/
14
15
D5 or
INVSYNC
DI/O
DI/O
When SER/PAR is LOW, this output is used as Bit 5 of the parallel port data output bus.
When SER/PAR is HIGH, this input, part of the serial port, is used to select the active state of the SYNC
signal. It is active in both master and slave modes. When LOW, SYNC is active HIGH. When HIGH, SYNC
is active LOW.
When SER/PAR is LOW, this output is used as Bit 6 of the parallel port data output bus.
When SER/PAR is HIGH, this input, part of the serial port, is used to invert the SCLK signal. It is active in
both master and slave modes.
D6 or
INVSCLK
Rev. 0 | Page 8 of 28
AD7652
Pin No. Mnemonic
Type1 Description
16
D7 or
DI/O
When SER/PAR is LOW, this output is used as Bit 7 of the parallel port data output bus.
RDC/SDIN
When SER/PAR is HIGH, this input, part of the serial port, is used as either an external data input or a
read mode selection input depending on the state of EXT/INT.
When EXT/INT is HIGH, RDC/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 DATA
with a delay of 16 SCLK periods after the initiation of the read sequence.
When EXT/INT is LOW, RDC/SDIN is used to select the read mode. When RDC/SDIN is HIGH, the data is
output on SDOUT during conversion. When RDC/SDIN is LOW, the data can be output on SDOUT only
when the conversion is complete.
17
18
19
20
21
OGND
OVDD
DVDD
DGND
D8 or
SDOUT
P
P
P
P
Input/Output Interface Digital Power Ground.
Input/Output Interface Digital Power. Nominally at the same supply as the host interface (5 V or 3 V).
Digital Power. Nominally at 5 V.
Digital Power Ground.
DO
When SER/PAR is LOW, this output is used as Bit 8 of the parallel port data output bus.
When SER/PAR is HIGH, this output, part of the serial port, is used as a serial data output synchronized
to SCLK. Conversion results are stored in an on-chip register. The AD7652 provides the conversion
result, MSB first, from its internal shift register. The DATA format is determined by the logic level of
OB/2C. In serial mode when EXT/INT is LOW, SDOUT is valid on both edges of SCLK. In serial mode
when EXT/INT is HIGH, if INVSCLK is LOW, SDOUT is updated on the SCLK rising edge and valid on the
next falling edge; if INVSCLK is HIGH, SDOUT is updated on the SCLK falling edge and valid on the next
rising edge.
22
23
D9 or
SCLK
DI/O
DO
When SER/PAR is LOW, this output is used as Bit 9 of the parallel port data or SCLK output bus.
When SER/PAR is HIGH, this pin, part of the serial port, is used as a serial data clock input or output,
depending upon the logic state of the EXT/INT pin. The active edge where the data SDOUT is updated
depends upon the logic state of the INVSCLK pin.
D10 or
SYNC
When SER/PAR is LOW, this output is used as Bit 10 of the parallel port data output bus.
When SER/PAR is HIGH, this output, part of the serial port, is used as a digital output frame
synchronization for use with the internal data clock (EXT/INT = logic LOW). When a read sequence is
initiated and INVSYNC is LOW, SYNC is driven HIGH and remains HIGH while the SDOUT output is
valid. When a read sequence is initiated and INVSYNC is HIGH, SYNC is driven LOW and remains LOW
while the SDOUT output is valid.
24
D11 or
RDERROR
DO
When SER/PAR is LOW, this output is used as Bit 11 of the parallel port data output bus. When
SER/PAR and EXT/INT are HIGH, this output, part of the serial port, is used as an incomplete read error
flag. In slave mode, when a data read is started and not complete when the following conversion is
complete, the current data is lost and RDERROR is pulsed HIGH.
25–28
29
D[12:15]
BUSY
DO
DO
Bit 12 to Bit 15 of the Parallel Port Data Output Bus. These pins are always outputs regardless of the
state of SER/PAR.
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 could be
used as a data ready clock signal.
30
31
32
DGND
RD
P
DI
DI
Must Be Tied to Digital Ground.
Read Data. When CS and RD are both LOW, the interface parallel or serial output bus is enabled.
CS
Chip Select. When CS and RD are both LOW, the interface parallel or serial output bus is enabled. CS is
also used to gate the external clock.
33
34
35
RESET
PD
DI
DI
DI
Reset Input. When set to a logic HIGH, this pin resets the AD7652 and the current conversion, if any, is
aborted. If not used, this pin could be tied to DGND.
Power-Down Input. When set to a logic HIGH, power consumption is reduced and conversions are
inhibited after the current one is completed.
Start Conversion. If CNVST is HIGH when the acquisition phase (t8) is complete, the next falling edge
on CNVST puts the internal sample/hold into the hold state and initiates a conversion. The mode is
most appropriate if low sampling jitter is desired. If CNVST is LOW when the acquisition phase (t8) is
complete, the internal sample/hold is put into the hold state and a conversion is immediately started.
Reference Input Voltage. On-chip reference output voltage.
CNVST
37
38
39
43
REF
AI/O
AI
AI
REFGND
INGND
IN
Reference Input Analog Ground.
Analog Input Ground.
Primary Analog Input with a Range of 0 V to 2.5 V.
AI
Rev. 0 | Page 9 of 28
AD7652
Pin No. Mnemonic
Type1 Description
45
46
47
TEMP
REFBUFIN
PDREF
AO
AI/O
DI
Temperature Sensor Voltage Output.
Reference Input Voltage. The reference output and the reference buffer input.
This pin allows the choice of internal or external voltage references. When LOW, the on-chip reference
is turned on. When HIGH, the internal reference is switched off and an external reference must be
used.
48
PDBUF
DI
This pin allows the choice of buffering an internal or external reference with the internal buffer. When
LOW, the buffer is selected. When HIGH, the buffer is switched off.
1AI = 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
AD7652
DEFINITIONS OF SPECIFICATIONS
Integral Nonlinearity Error (INL)
Total Harmonic Distortion (THD)
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 LSB beyond the last code transition. The deviation is
measured from the middle of each code to the true straight line.
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.
Signal-to-Noise Ratio (SNR)
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.
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.
Signal-to-(Noise + Distortion) Ratio (S/[N+D])
S/(N+D) 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 S/(N+D) is expressed in decibels.
Full-Scale Error
The last transition (from 011…10 to 011…11 in twos
complement coding) should occur for an analog voltage 1½ LSB
below the nominal full scale (2.49994278 V for the 0 V to 2.5 V
range). The full-scale error is the deviation of the actual level of
the last transition from the ideal level.
Aperture Delay
Aperture delay is a measure of the acquisition performance and
is measured from the falling edge of the
input to when
CNVST
the input signal is held for a conversion.
Unipolar Zero Error
Transient Response
The first transition should occur at a level ½ LSB above analog
ground (19.073 µV for the 0 V to 2.5 V range). Unipolar zero
error is the deviation of the actual transition from that point.
Transient response is the time required for the AD7652 to
achieve its rated accuracy after a full-scale step function is
applied to its input.
Spurious-Free Dynamic Range (SFDR)
Overvoltage Recovery
SFDR is the difference, in decibels (dB), between the rms
amplitude of the input signal and the peak spurious signal.
Overvoltage recovery is the time required for the ADC to
recover to full accuracy after an analog input signal 150% of the
full-scale value is reduced to 50% of the full-scale value.
Effective Number of Bits (ENOB)
ENOB is a measurement of the resolution with a sine wave
input. It is related to S/(N+D) by the following formula:
Reference Voltage Temperature Coefficient
Reference voltage temperature coefficient is the change of
internal reference voltage output voltage V over the operating
temperature range and normalized by the output voltage at
25°C, expressed in ppm/°C. The equation follows:
ENOB = (S/[N+D]dB – 1.76)/6.02
and is expressed in bits.
V(T2)–V(T1)
V(25°C)×(T2 –T1)
TCV(ppm/ °C) =
×106
where:
V(25°C) = V at +25°C
V(T2) = V at Temperature 2 (+85°C)
V(T1) = V at Temperature 1 (–40°C)
Rev. 0 | Page 11 of 28
AD7652
TYPICAL PERFORMANCE CHARACTERISTICS
2.0
1.5
1.0
0.5
0
4
3
2
1
0
–1
–2
–3
–4
–0.5
–1.0
0
16384
32768
CODE
49152
65536
0
16384
32768
CODE
49152
65536
02966-0-026
02965-0-023
Figure 8. Differential Nonlinearity vs. Code
Figure 5. Integral Nonlinearity vs. Code
160000
140000
120000
100000
80000
60000
40000
20000
0
140000
120000
100000
80000
60000
40000
20000
0
144958
111974 112112
64967
41624
25889
10598
8659
801
477
110
70
0
0
0
0
0
1
0
7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
7FFB 7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004
CODE IN HEX
CODE IN HEX
02965-0-028
02965-0-027
Figure 9. Histogram of 261,120 Conversions of a
DC Input at the Code Center
Figure 6. Histogram of 261,120 Conversions of a
DC Input at the Code Transition
14.5
14.0
13.5
13.0
12.5
88
85
82
79
76
0
–20
fS = 500kSPS
fIN = 102kHz
SNR = 83.4dB
THD = 90.9dB
SFDR = 91.2dB
S/[N+D] = 82.8dB
–40
SNR
–60
–80
–100
–120
–140
–160
–180
S/[N+D]
ENOB
0
50
100
150
200
250
1
10
100
1000
FREQUENCY (kHz)
FREQUENCY (kHz)
02965-0-030
02965-0-029
Figure 10. SNR, S/(N+D), and ENOB vs. Frequency
Figure 7. FFT Plot
Rev. 0 | Page 12 of 28
AD7652
140
120
100
80
–100
–105
–110
–115
–120
–50
–60
SFDR
THD
–70
SECOND
HARMONIC
–80
60
–90
40
–100
–110
–120
THD
THIRD
THIRD
HARMONIC
HARMONIC
20
SECOND
HARMONIC
0
5
85
–55
–35
–15
25
45
65
125
105
1
10
100
1000
TEMPERATURE (°C)
FREQUENCY (kHz)
02965-0-034
02966-0-031
Figure 14. THD and Harmonics vs. Temperature
Figure 11. THD, Harmonics, and SFDR vs. Frequency
87
86
85
84
83
82
10000
1000
100
10
AVDD
DVDD
OVDD
SNR
1
S/[N+D]
0.1
0.01
PDREF = PDBUF = HIGH
10000 100000 1000000
0.001
10
100
1000
–60
–50
–40
–30
–20
–10
0
SAMPLE RATE (SPS)
INPUT LEVEL (dB)
02965-0-036
02965-0-032
Figure 12. SNR and S/(N+D) vs. Input Level (Referred to Full Scale)
Figure 15. Operating Current vs. Sample Rate
6
5
14.50
14.38
14.25
14.13
14.00
89
4
3
88
SNR
2
FULL SCALE
S[N+D]
1
0
87
ENOB
–1
–2
–3
–4
–5
–6
ZERO ERROR
86
85
–55 –35
5
25
45
65
85
125
5
85
105
–15
–55
–35
–15
25
45
65
125
105
TEMPERATURE (°C)
TEMPERATURE (°C)
02965-0-040
02965-0-033
Figure 16. Zero Error, Full Scale with Reference vs. Temperature
Figure 13. SNR, S/(N+D), and ENOB vs. Temperature
Rev. 0 | Page 13 of 28
AD7652
2.5000
2.4995
2.4990
2.4985
2.4980
2.4975
2.4970
50
40
30
20
10
0
OVDD= 2.7V @ 85°C
OVDD= 2.7V @ 25°C
OVDD= 5V @ 85°C
OVDD= 5V @ 25°C
–40
–20
0
20
40
60
80
100
120
0
50
100
(pF)
150
200
TEMPERATURE (°C)
C
L
02965-0-039
02966-0-035
Figure 17. Typical Reference Output Voltage vs. Temperature
Figure 19. Typical Delay vs. Load Capacitance CL
20
18
16
14
12
10
8
6
4
2
0
–30 –26 –22 –18 –14 –10 –6 –2
2
6
10 14 18 22 26 30
REFERENCE DRIFT (ppm/°C)
02965-0-040
Figure 18. Reference Voltage Temperature Coefficient Distribution (100 Units)
Rev. 0 | Page 14 of 28
AD7652
CIRCUIT INFORMATION
IN
REF
REFGND
SWITCHES
CONTROL
SW
MSB
32,768C 16,384C
LSB
A
4C
2C
C
C
BUSY
CONTROL
COMP
LOGIC
INGND
OUTPUT
CODE
65,536C
SW
B
CNVST
02964-0-005
Figure 20. ADC Simplified Schematic
The AD7652 is a very fast, low power, single supply, precise
16-bit analog-to-digital converter (ADC).
During the acquisition phase, the common terminal of the array
tied to the comparator's positive input is connected to AGND
via SWA. All independent switches are connected to the analog
input IN. Thus, the capacitor array is used as a sampling
capacitor and acquires the analog signal on IN. Similarly, the
dummy capacitor acquires the analog signal on INGND.
The AD7652 provides the user with an on-chip track/hold,
successive approximation ADC that does not exhibit any
pipeline or latency, making it ideal for multiple multiplexed
channel applications.
When
goes LOW, a conversion phase is initiated. When
CNVST
The AD7652 can be operated from a single 5 V supply and can
be interfaced to either 5 V or 3 V digital logic. It is housed in
either a 48-lead LQFP or a 48-lead LFCSP that saves space and
allows flexible configurations as either a serial or parallel inter-
face. The AD7652 is pin-to-pin compatible with PulSAR ADCs.
the conversion phase begins, SWA and SWB are opened. The
capacitor array and dummy capacitor are then disconnected
from the inputs and connected to REFGND. Therefore, the
differential voltage between IN and INGND 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, …VREF/65536). The control logic toggles these
switches, starting with the MSB, to bring the comparator back
into a balanced condition.
CONVERTER OPERATION
The AD7652 is a successive-approximation ADC based on a
charge redistribution DAC. Figure 20 shows a simplified sche-
matic of the ADC. The capacitive DAC consists of an array of 16
binary weighted capacitors and an additional LSB capacitor. The
comparator’s negative input is connected to a dummy capacitor
of the same value as the capacitive DAC array.
After this process is completed, the control logic generates the
ADC output code and brings the BUSY output LOW.
Rev. 0 | Page 15 of 28
AD7652
Table 7. Output Codes and Ideal Input Voltages
Digital Output Code (Hex)
Transfer Functions
2C
Using the OB/ digital input, the AD7652 offers two output
Analog
Input
2.499962 V FFFF1
2.499923 V FFFE
1.250038 V 8001
Straight
Binary
Twos
Complement
codings: straight binary and twos complement. The LSB size is
VREF/65536, which is about 38.15 µV. The AD7652’s ideal
transfer characteristic is shown in Figure 21 and Table 7.
Description
FSR –1 LSB
FSR – 2 LSB
Midscale + 1 LSB
Midscale
7FFF1
7FFE
0001
0000
FFFF
8001
80002
1 LSB =V
/65536
REF
1.25 V
8000
111...111
111...110
111...101
Midscale – 1 LSB
–FSR + 1 LSB
–FSR
1.249962 V 7FFF
38 µV
0 V
0001
00002
1This is also the code for overrange analog input (VIN – VINGND above
VREF – VREFGND).
2This is also the code for underrange analog input (VIN below VINGND).
000...010
000...001
000...000
0V
1 LSB
V
– 1 LSB
REF
– 1.5 LSB
0.5 LSB
V
REF
ANALOG INPUT
02964-0-003
Figure 21. ADC Ideal Transfer Function
ANALOG
SUPPLY
(5V)
20Ω
DIGITAL SUPPLY
(3.3V OR 5V)
+
+
+
100nF
100nF
100nF
10µF
10µF
10µF
AVDD
DGND DVDD
OVDD
OGND
GND
SERIAL
PORT
SCLK
REF
SDOUT
4
2
1
C
REFBUFIN
R
100nF
µC/µP/DSP
REFGND
BUSY
AD7652
3
CNVST
D
15Ω
U1
IN
OB/2C
ANALOG INPUT
(0VTO 2.5V)
DVDD
SER/PAR
C
2.7nF
C
INGND
PD
PDBUF RESET
CS
RD
BYTESWAP
PDREF
CLOCK
NOTES
1
THE CONFIGURATION SHOWN IS USING THE INTERNAL REFERENCE AND INTERNAL BUFFER.
THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
OPTIONAL LOW JITTER.
2
3
4
A 10µF CERAMIC CAPACITOR (X5R, 1206 SIZE) IS RECOMMENDED (e.g., PANASONIC ECJ3YB0J106M).
SEE VOLTAGE REFERENCE INPUT SECTION.
02965-0-004
Figure 22. Typical Connection Diagram
Rev. 0 | Page 16 of 28
AD7652
Driver Amplifier Choice
TYPICAL CONNECTION DIAGRAM
Figure 22 shows a typical connection diagram for the AD7652.
Analog Input
Although the AD7652 is easy to drive, the driver amplifier needs
to meet the following requirements:
Figure 23 shows an equivalent circuit of the input structure of
the AD7652.
•
The driver amplifier and the AD7652 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’s data
sheet, settling at 0.1% to 0.01% is more commonly speci-
fied. This could differ significantly from the settling time at
a 16-bit level and should be verified prior to driver
selection. The tiny op amp AD8021, which combines
ultralow noise and high gain-bandwidth, meets this settling
time requirement even when used with gains up to 13.
The two diodes, D1 and D2, provide ESD protection for the
analog inputs IN and INGND. Care must be taken to ensure
that the analog input signal never exceeds the supply rails by
more than 0.3 V. This will cause these diodes to become
forward-biased and 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) 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.
•
•
The noise generated by the driver amplifier needs to be
kept as low as possible in order to preserve the SNR and
transition noise performance of the AD7652. The noise
coming from the driver is filtered by the AD7652 analog
input circuit 1-pole low-pass filter made by R1 and C2 or
by the external filter, if one is used.
AVDD
D1
D2
C2
R1
IN
OR INGND
C1
The driver needs to have a THD performance suitable to
that of the AD7652.
AGND
02965-0-008
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.
Figure 23. Equivalent Analog Input Circuit
This analog input structure allows the sampling of the
differential signal between IN and INGND. Unlike other
converters, INGND is sampled at the same time as IN. By using
this differential input, small signals common to both inputs are
rejected. For instance, by using INGND to sense a remote signal
ground, ground potential differences between the sensor and
the local ADC ground are eliminated.
The AD8022 could also be used if a dual version is needed and
gain of +1 is present. The AD829 is an alternative in
applications where high frequency (above 100 kHz)
performance is not required. In gain of 1 applications, it requires
an 82 pF compensation capacitor. The AD8610 is an option
when low bias current is needed in low frequency applications.
During the acquisition phase, the impedance of the analog input
IN can be modeled as a parallel combination of capacitor C1
and the network formed by the series connection of R1 and C2.
C1 is primarily the pin capacitance. R1 is typically 168 Ω and is
a lumped component made up of some serial resistors and the
on resistance of the switches. C2 is typically 60 pF and is mainly
the ADC sampling capacitor. During the conversion phase,
when the switches are opened, the input impedance is limited to
C1. R1 and C2 make a 1-pole low-pass filter that reduces
undesirable aliasing effect and limits the noise.
When the source impedance of the driving circuit is low, the
AD7652 can be driven directly. Large source impedances will
significantly affect the ac performance, especially total
harmonic distortion.
Rev. 0 | Page 17 of 28
AD7652
For applications that use multiple AD7652s, it is more effective
to use the internal buffer to buffer the reference voltage.
Voltage Reference Input
The AD7652 allows the choice of either a very low temperature
drift internal voltage reference or an external 2.5 V reference.
Care should be taken with the voltage reference’s temperature
coefficient, which directly affects the full-scale accuracy if this
parameter matters. For instance, a 15 ppm/°C temperature
coefficient of the reference changes full scale by 1 LSB/°C.
Unlike many ADCs with internal references, the internal
reference of the AD7652 provides excellent performance and
can be used in almost all applications.
Note that VREF can be increased to AVDD – 1.85 V. Since the
input range is defined in terms of VREF, this would essentially
increase the range to 0 V to 3 V with an AVDD above 4.85 V.
The AD780 can be selected with a 3 V reference voltage.
To use the internal reference along with the internal buffer,
PDREF and PDBUF should both be LOW. This will produce a
1.207 V voltage on REFBUFIN which, amplified by the buffer,
will result in a 2.5 V reference on the REF pin.
The TEMP pin, which measures the temperature of the AD7652,
can be used as shown in Figure 24. The output of TEMP pin is
applied to one of the inputs of the analog switch (e.g., ADG779),
and the ADC itself is used to measure its own temperature. This
configuration is very useful for improving the calibration
accuracy over the temperature range.
The output impedance of REFBUFIN is 11 kΩ (minimum) when
the internal reference is enabled. It is useful to decouple
REFBUFIN with a 100 nF ceramic capacitor. Thus, the 100 nF
capacitor provides an RC filter for noise reduction.
To use an external reference along with the internal buffer,
PDREF should be HIGH and PDBUF should be LOW. This
powers down the internal reference and allows the 2.5 V
reference to be applied to REFBUFIN.
TEMP
ADG779
TEMPERATURE
SENSOR
IN
ANALOG INPUT
(UNIPOLAR)
To use an external reference directly on REF pin, PDREF and
PDBUF should both be HIGH.
AD7652
C
AD8021
C
02965-0-024
PDREF and PDBUF respectively power down the internal
reference and the internal reference buffer. Note that the PDREF
and PDBUF input current should never exceed 20 mA. This
could eventually occur when input voltage is above AVDD (for
instance at power up). In this case, a 100 Ω series resistor is
recommended.
Figure 24. Temperature Sensor Connection Diagram
Power Supply
The AD7652 uses three power supply pins: an analog 5 V supply
AVDD, a digital 5 V core supply DVDD, and a digital
input/output interface supply OVDD. OVDD allows direct
interface with any logic between 2.7 V and DVDD + 0.3 V. To
reduce the supplies needed, the digital core (DVDD) can be
supplied through a simple RC filter from the analog supply, as
shown in Figure 22. The AD7652 is independent of power
supply sequencing once OVDD does not exceed DVDD by
more than 0.3 V, and is thus free of supply voltage induced
latch-up.
The internal reference is temperature compensated to 2.5 V
20 mV. The reference is trimmed to provide a typical drift of 7
ppm/°C. This typical drift characteristic is shown in Figure 17.
For improved drift performance, an external reference such as
the AD780 can be used.
The AD7652 voltage reference input REF has a dynamic input
impedance; it should therefore 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 tanta-
lum capacitor) is appropriate when using either the internal
reference or one of these recommended reference voltages:
•
•
•
The low noise, low temperature drift ADR421 and AD780
The low power ADR291
The low cost AD1582
Rev. 0 | Page 18 of 28
AD7652
POWER DISSIPATION VERSUS THROUGHPUT
Operating currents are very low during the acquisition phase,
allowing significant power savings when the conversion rate is
reduced (see Figure 25). The AD7652 automatically reduces its
power consumption at the end of each conversion phase. This
makes the part ideal for very low power battery applications.
The digital interface and the reference remain active even
during the acquisition phase. To reduce operating digital supply
currents even further, digital inputs need to be driven close to
the power supply rails (i.e., DVDD or DGND), and OVDD
should not exceed DVDD by more than 0.3 V.
The
trace should be shielded with ground and a low
CNVST
value serial resistor (i.e., 50 Ω) termination should be added
close to the output of the component that drives this line.
For applications where SNR is critical, the
signal should
CNVST
have very low jitter. This may be achieved by using a dedicated
oscillator for generation, or to clock with a
CNVST
CNVST
high frequency, low jitter clock, as shown in Figure 22.
t2
t1
100000
10000
1000
CNVST
BUSY
t4
t3
t6
t5
MODE ACQUIRE
CONVERT
t7
ACQUIRE
t8
CONVERT
02964-0-011
100
Figure 26. Basic Conversion Timing
PDREF = PDBUF = HIGH
10
1000
10
100
10000
100000
1000000
t9
SAMPLE RATE (SPS)
02965-0-037
RESET
Figure 25. Power Dissipation vs. Sampling Rate
BUSY
DATA
CONVERSION CONTROL
Figure 26 shows the detailed timing diagrams of the conversion
process. The AD7652 is controlled by the signal, which
CNVST
t8
initiates conversion. Once initiated, it cannot be restarted or
aborted, even by the power-down input PD, until the conversion
CNVST
is complete.
operates independently of
and .
CNVST
CS
RD
02964-0-011
Figure 27. RESET Timing
Conversions can be automatically initiated with the AD7652. If
is held LOW when BUSY is LOW, the AD7652 controls
CNVST
the acquisition phase and automatically initiates a new
conversion. By keeping LOW, the AD7652 keeps the
CS = RD = 0
CNVST
t1
CNVST
conversion process running by itself. It should be noted that the
analog input must be settled when BUSY goes LOW. Also, at
t10
power-up,
should be brought LOW once to initiate the
CNVST
BUSY
t4
conversion process. In this mode, the AD7652 can run slightly
faster than the guaranteed 500 kSPS.
t3
t11
DATA
BUS
PREVIOUS CONVERSION DATA
NEW DATA
Although
is a digital signal, it should be designed with
CNVST
special care with fast, clean edges, and levels with minimum
overshoot and undershoot or ringing.
02964-0-012
Figure 28. Master Parallel Data Timing for Reading (Continuous Read)
Rev. 0 | Page 19 of 28
AD7652
DIGITAL INTERFACE
CS
RD
The AD7652 has a versatile digital interface; it can be interfaced
with the host system by using either a serial or a parallel
interface. The serial interface is multiplexed on the parallel data
bus. The AD7652 digital interface also accommodates both 3 V
and 5 V logic by simply connecting the OVDD supply pin of the
AD7652 to the host system interface digital supply. Finally, by
BUSY
using the OB/ input pin, both twos complement or straight
2C
binary coding can be used.
DATA
BUS
CURRENT
CONVERSION
The two signals,
and
, control the interface.
RD
and
CS RD
CS
t12
t13
have a similar effect because they are OR’d together internally.
When at least one of these signals is HIGH, the interface
02964-0-013
outputs are in high impedance. Usually
allows the selection
CS
of each AD7652 in multicircuit applications and is held LOW in
a single AD7652 design. is generally used to enable the
Figure 29. Slave Parallel Data Timing for Reading (Read after Convert)
RD
CS = 0
conversion result on the data bus.
CNVST,
RD
t1
PARALLEL INTERFACE
The AD7652 is configured to use the parallel interface when
SER/
is held LOW. The data can be read either after each
PAR
BUSY
t4
conversion, which is during the next acquisition phase, or
during the following conversion, as shown in Figure 29 and
Figure 30, respectively. When the data is read during the
conversion, however, 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.
t3
DATA
BUS
PREVIOUS
CONVERSION
t12
t13
02964-0-014
Figure 30. Slave Parallel Data Timing for Reading (Read during Convert)
The BYTESWAP pin allows a glueless interface to an 8-bit bus.
As shown in Figure 31, the LSB byte is output on D[7:0] and the
MSB is output on D[15:8] when BYTESWAP is LOW. 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].
CS
RD
BYTESWAP
SERIAL INTERFACE
HI-Z
HI-Z
HI-Z
PINS D[15:8]
PINS D[7:0]
HIGH BYTE
t12
LOW BYTE
LOW BYTE
t12
HIGH BYTE
The AD7652 is configured to use the serial interface when
SER/
is held HIGH. The AD7652 outputs 16 bits of data,
t13
PAR
HI-Z
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 edges of the data clock.
02965-0-025
Figure 31. 8-Bit Parallel Interface
Rev. 0 | Page 20 of 28
AD7652
Usually, because the AD7652 is used with a fast throughput,
MASTER SERIAL INTERFACE
Master Read During Conversion is the most recommended
serial mode. In this mode mode, the serial clock and data toggle
at appropriate instants, minimizing potential feedthrough
between digital activity and critical conversion decisions.
Internal Clock
The AD7652 is configured to generate and provide the serial
data clock SCLK when the EXT/
pin is held LOW. The
INT
AD7652 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
RDC/SDIN input, the data can be read after each conversion or
during the following conversion. Figure 32 and Figure 33 show
the detailed timing diagrams of these two modes.
In Read After Conversion mode, it should be noted that unlike
in other modes, the BUSY signal returns LOW after the 16 data
bits are pulsed out and not at the end of the conversion phase,
which results in a longer BUSY width.
RDC/SDIN = 0
INVSCLK = INVSYNC = 0
EXT/INT = 0
CS, RD
t3
CNVST
t28
BUSY
t30
t29
t25
SYNC
t14
t18
t19
t24
t20
t21
t26
1
2
3
14
15
16
SCLK
t15
t27
SDOUT
D15
D14
t23
D2
D1
D0
X
t16
t22
02964-0-015
Figure 32. Master Serial Data Timing for Reading (Read after Convert)
EXT/INT = 0
RDC/SDIN = 1
INVSCLK = INVSYNC = 0
CS, RD
CNVST
BUSY
t1
t3
t17
t25
SYNC
t14
t19
t20 t21
t24
t26
t15
SCLK
1
2
3
14
15
16
t18
t27
SDOUT
X
D15
D14
t23
D2
D1
D0
t16
t22
02964-0-016
Figure 33. Master Serial Data Timing for Reading (Read Previous Conversion during Convert
Rev. 0 | Page 21 of 28
AD7652
SLAVE SERIAL INTERFACE
External Clock
While the AD7652 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 AD7652 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
recommended 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.
The AD7652 is configured to accept an externally supplied
serial data clock on the SCLK pin when the EXT/
pin is held
INT
HIGH. In this mode, several methods can be used to read the
data. The external serial clock is gated by . When and
RD
CS
CS
are both LOW, the data can be read after each conversion or
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 34 and Figure 35 show the detailed timing
diagrams of these methods.
RD = 0
EXT/INT = 1
INVSCLK = 0
RD
BUSY
t35
t36 t37
SCLK
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
02964-0-017
Figure 34. Slave Serial Data Timing for Reading (Read after Convert)
RD = 0
EXT/INT = 1
INVSCLK = 0
CS
CNVST
BUSY
t3
t35
t36 t37
SCLK
1
2
3
14
15
16
t31
t32
D14
X
D1
SDOUT
D15
D13
D0
t16
02965-0-018
Figure 35. Slave Serial Data Timing for Reading (Read Previous Conversion during Convert)
Rev. 0 | Page 22 of 28
AD7652
External Discontinuous Clock Data Read After
Conversion
External Clock Data Read During Conversion
Figure 35 shows the detailed timing diagrams of this method.
During a conversion, while both and are both 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 edges of the clock. The 16 bits must 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 the 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 34 shows the detailed timing diagrams of this method.
After a conversion is complete, indicated by BUSY returning
CS
RD
LOW, the conversion’s result can be read while both
and
CS
RD
are LOW. Data is shifted out MSB first with 16 clock pulses and
is valid on the rising and falling edges of the clock.
Among the advantages of this method is the fact that conversion
performance is not degraded because there are no voltage tran-
sients on the digital interface during the conversion process.
Another advantage is the ability to read the data at any speed up
to 40 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 18 MHz is recommended to
ensure that all the bits are read during the first half of the
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. This allows the use of a slower
clock speed like 14 MHz.
Finally, in this mode only, the AD7652 provides a daisy-chain
feature using the RDC/SDIN pin for cascading multiple
converters together. This feature is useful for reducing
component count and wiring connections when desired, as, for
instance, in isolated multiconverter applications.
An example of the concatenation of two devices is shown in
Figure 36. Simultaneous sampling is possible by using a
common
signal. It should be noted that the RDC/SDIN
CNVST
input is latched on the opposite edge of SCLK of the one used to
shift out the data on SDOUT. Therefore, the MSB of the
“upstream” converter just follows the LSB of the “downstream”
converter on the next SCLK cycle.
BUSY
OUT
BUSY
BUSY
AD#72652
AD#71652
(UPSTREAM)
(DOWNSTREAM)
DATA
OUT
RDC/SDIN
SDOUT
RDC/SDIN
SDOUT
CNVST
CS
CNVST
CS
SCLK
SCLK
SCLK IN
CS IN
CNVST IN
02965-0-019
Figure 36. Two AD7652s in a Daisy-Chain Configuration
Rev. 0 | Page 23 of 28
AD7652
(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). To meet all timing
requirements, the SPI clock should be limited to 17 Mbps, which
allows it to read an ADC result in less than 1 µs. When a higher
sampling rate is desired, use of one of the parallel interface
modes is recommended.
MICROPROCESSOR INTERFACING
The AD7652 is ideally suited for traditional dc measurement
applications supporting a microprocessor, and for ac signal
processing applications interfacing to a digital signal processor.
The AD7652 is designed to interface either 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 AD7652 to prevent digital noise from coupling
into the ADC. The following section discusses the use of an
AD7652 with an ADSP-219x SPI equipped DSP.
DVDD
ADSP-219x*
AD7652*
SER/PAR
EXT/INT
SPI Interface (ADSP-219x)
Figure 37 shows an interface diagram between the AD7652 and
the SPI equipped ADSP-219x. To accommodate the slower
speed of the DSP, the AD7652 acts as a slave device and data
must be read after conversion. This mode also allows the daisy-
chain feature. The convert command can be initiated in
response to an internal timer interrupt. 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 inter-
face (SPI) on the ADSP-219x is configured for master mode—
BUSY
CS
SDOUT
SCLK
CNVST
PFx
SPIxSEL (PFx)
MISOx
SCKx
PFx or TFSx
RD
INVSCLK
*ADDITIONAL PINS OMITTED FOR CLARITY
02965-0-021
Figure 37. Interfacing the AD7652 to an SPI Interface
Rev. 0 | Page 24 of 28
AD7652
APPLICATION HINTS
BIPOLAR AND WIDER INPUT RANGES
Running digital lines under the device should be avoided since
these will couple noise onto the die. The analog ground plane
should be allowed to run under the AD7652 to avoid noise
In some applications, it is desirable to use a bipolar or wider
analog input range such as 10 V, 5 V, or 0 V to 5 V. Although
the AD7652 has only one unipolar range, simple modifications
of input driver circuitry allow bipolar and wider input ranges to
be used without any performance degradation. Figure 38 shows
a connection diagram that allows this. Component values
required and resulting full-scale ranges are shown in Table 8.
coupling. Fast switching signals like
or clocks should be
CNVST
shielded with digital ground to avoid radiating noise to other
sections of the board, and should never run near analog signal
paths. Crossover of digital and analog signals should be avoided.
Traces on different but close layers of the board should run at
right angles to each other. This will reduce the effect of crosstalk
through the board.
When desired, accurate gain and offset can be calibrated by
acquiring a ground and voltage reference using an analog
multiplexer (U2), as shown in Figure 38.
The power supply lines to the AD7652 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 supply’s impedance presented to the
AD7652 and to reduce the magnitude of the supply spikes.
Decoupling ceramic capacitors, typically 100 nF, should be
placed on each power supply pin—AVDD, DVDD, and
OVDD—close to, and ideally right up against these pins and
their corresponding ground pins. Additionally, low ESR 10 µF
capacitors should be located near the ADC to further reduce
low frequency ripple.
C
F
R1
R2
ANALOG
INPUT
15Ω
2.7nF
IN
U1
AD7652
U2
100nF
R3
R4
INGND
REF
The DVDD supply of the AD7652 can be a separate supply or
can come from the analog supply AVDD or the digital interface
supply OVDD. When the system digital supply is noisy or when
fast switching digital signals are present, if no separate supply is
available, the user should connect DVDD to AVDD through an
RC filter (see Figure 22) and the system supply to OVDD and
the remaining digital circuitry. When DVDD is powered from
the system supply, it is useful to insert a bead to further reduce
high frequency spikes.
C
REF
REFGND
02965-0-022
Figure 38. Using the AD7652 in 16-Bit Bipolar and/or Wider Input Ranges
Table 8. Component Values and Input Ranges
Input Range
R1 (Ω)
R2 (kΩ)
R3 (kΩ)
R4 (kΩ)
The AD7652 has five different ground pins: INGND, REFGND,
AGND, DGND, and OGND. INGND is used to sense the analog
input signal. 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.
10 V
5 V
0 V to –5 V
500
500
500
4
2
1
2.5
2.5
None
2
1.67
0
LAYOUT
The AD7652 has very good immunity to noise on the power
supplies. However, care should still be taken with regard to
grounding layout.
The printed circuit board that houses the AD7652 should be
designed so the analog and digital sections are separated and
confined to certain areas of the board. This facilitates the use of
ground planes that can be separated easily. Digital and analog
ground planes should be joined in only one place, preferably
underneath the AD7652, or as close as possible to the AD7652.
If the AD7652 is in a system where multiple devices require
analog-to-digital ground connections, the connection should
still be made at one point only, a star ground point that should
be established as close as possible to the AD7652.
EVALUATING THE AD7652’S PERFORMANCE
A recommended layout for the AD7652 is outlined in the
EVAL-AD7652 evaluation board for the AD7652. 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 BRD2.
Rev. 0 | Page 25 of 28
AD7652
Preliminary Technical Data
OUTLINE DIMENSIONS
0.75
0.60
0.45
9.00 BSC
SQ
1.60
MAX
37
36
48
1
PIN 1
SEATING
PLANE
10°
6°
7.00
TOP VIEW
1.45
1.40
1.35
0.20
0.09
(PINS DOWN )
BSC SQ
2°
VIEW A
7°
3.5°
0°
25
12
0.15
0.05
24
13
SEATING
PLANE
0.10 MAX
0.27
0.22
0.17
0.50
BSC
COPLANARITY
VIEW A
ROTATED 90
°
CCW
COMPLIANT TO JEDEC STANDARDS MS-026BBC
Figure 39. 48-Lead Quad Flatpack (LQFP) [ST-48]
Dimensions shown in millimeters
0.30
0.23
0.18
7.00
0.60 MAX
0.60 MAX
BSC SQ
PIN 1
INDICATOR
37
36
48
1
PIN 1
INDICATOR
5.25
6.75
BOTTOM
VIEW
TOP
VIEW
BSC SQ
5.10 SQ
4.95
0.50
0.40
0.30
25
24
12
13
0.25 MIN
5.50
REF
0.80 MAX
0.65 TYP
PADDLE CONNECTED TO AGND.
THIS CONNECTION IS NOT
REQUIRED TO MEET THE
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 40. 48-Lead Frame Chip Scale Package (LFCSP) [CP-48]
Dimensions shown in millimeters
ORDERING GUIDE
Model
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Package Description
Quad Flatpack (LQFP)
Quad Flatpack (LQFP)
Lead Frame Chip Scale (LFCSP)
Lead Frame Chip Scale (LFCSP)
Evaluation Board
Package Option
AD7652AST
AD7652ASTRL
AD7652ACP
AD7652ACPRL
EVAL-AD7652CB1
EVAL-CONTROL BRD22
ST-48
ST-48
CP-48
CP-48
Controller Board
1This board can be used as a standalone evaluation board or in conjunction with the EVAL-CONTROL BRD2 for evaluation/demonstration purposes.
2This board allows a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators.
Rev. 0 | Page 26 of 28
AD7652
NOTES
Rev. 0 | Page 27 of 28
AD7652
NOTES
©
2003 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C02965–0–9/03(0)
Rev. 0 | Page 28 of 28
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