AD7988-1_17 [ADI]
16-Bit Lower Power PulSAR ADCs in MSOP/LFCSP;
| 型号： | AD7988-1_17 |
| 厂家： | 
ADI |
| 描述： | 16-Bit Lower Power PulSAR ADCs in MSOP/LFCSP |
| 文件： | 总24页 (文件大小：577K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
16-Bit Lower Power
PulSAR ADCs in MSOP/LFCSP
Data Sheet
AD7988-1/AD7988-5
FEATURES
GENERAL DESCRIPTION
Low power dissipation
AD7988-1
400 µW at 100 kSPS (VDD only)
700 µW at 100 kSPS (total)
AD7988-5
2 mW at 500 kSPS (VDD only)
3.5 mW at 500 kSPS (total)
16-bit resolution with no missing codes
Throughput: 100 kSPS/500 kSPS options
INL: 0.6 LSB typical, 1.25 LSB maximum
SINAD: 91.5 dB at 10 kHz
The AD7988-1/AD7988-51 are 16-bit, successive approximation,
analog-to-digital converters (ADC) that operate from a single
power supply, VDD. The AD7988-1 offers a 100 kSPS throughput,
and the AD7988-5 offers a 500 kSPS throughput. They are low
power, 16-bit sampling ADCs with a versatile serial interface
port. On the CNV rising edge, they sample an analog input,
IN+, between 0 V to VREF with respect to a ground sense, IN−.
The reference voltage, REF, is applied externally and can be set
independent of the supply voltage, VDD.
The SPI-compatible serial interface also features the ability to
daisy-chain several ADCs on a single 3-wire bus using the SDI
input. It is compatible with 1.8 V, 2.5 V, 3 V, or 5 V logic using
the separate supply, VIO.
THD: −114 dB at 10 kHz
Pseudo differential analog input range
0 V to VREF with VREF from 2.5 V to 5.0 V
No pipeline delay
Single-supply 2.5 V operation with 1.8 V/2.5 V/3 V/5 V logic
interface
The AD7988-1/AD7988-5 generics are housed in a 10-lead
MSOP or a 10-lead LFCSP with operation specified from −40°C
to +125°C.
Proprietary SPI-/QSPI™-/MICROWIRE™-/DSP-compatible
serial interface
Daisy-chain multiple ADCs
10-lead MSOP and 10-lead, 3 mm × 3 mm LFCSP, same space
as SOT-23
Table 1. MSOP, LFCSP, LGA 14-/16-/18-/20-Bit Precision
SAR ADCs and Integrated SAR ADC μModules®
μModule
400 kSPS
to
Data
Acquisition
Bits 100 kSPS
250 kSPS 500 kSPS
≥1000 kSPS System
Wide operating temperature range: −40°C to +125°C
201
181
AD40202
AD40032
AD40072
APPLICATIONS
AD7989-12 AD76912 AD40112
AD76902
Battery-powered equipment
Low power data acquisition systems
Portable medical instruments
ATE equipment
Data acquisitions
Communications
AD7989-52 AD79822
AD79842
AD76882
AD76932
AD79162
AD76862
161
163
AD7684
AD76872
AD40012
AD40052
AD79152
AD40002
AD7680
AD7683
AD7988-12
AD76852
AD7694
ADAQ7980
ADAQ7988
AD7988-52 AD40042
AD40082
AD79802
AD79832
143
AD7940
AD79422
AD79462
1 True differential.
2 Pin-for-pin compatible.
3 Pseudo differential.
1 Protected by U.S. Patent 6,703,961.
Rev. G
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Tel: 781.329.4700 ©2012–2017 Analog Devices, Inc. All rights reserved.
Technical Support
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AD7988-1/AD7988-5
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Connection Diagram ................................................... 16
Analog Inputs ............................................................................. 17
Driver Amplifier Choice ........................................................... 17
Voltage Reference Input ............................................................ 18
Power Supply............................................................................... 18
Digital Interface.......................................................................... 18
Applications....................................................................................... 1
General Description......................................................................... 1
Revision History ............................................................................... 2
Typical Application Circuit ............................................................. 3
Specifications..................................................................................... 4
Timing Specifications .................................................................. 6
Absolute Maximum Ratings............................................................ 8
ESD Caution.................................................................................. 8
Pin Configurations and Function Descriptions ........................... 9
Terminology .................................................................................... 10
Typical Performance Characteristics ........................................... 11
Theory of Operation ...................................................................... 15
Circuit Information.................................................................... 15
Converter Operation.................................................................. 15
CS
CS
Mode, 3-Wire........................................................................ 19
Mode 4-Wire......................................................................... 20
Chain Mode ................................................................................ 21
Applications Information.............................................................. 22
Interfacing to Blackfin® DSP..................................................... 22
Layout .......................................................................................... 22
Evaluating the Performance of the AD7988-1/AD7988-5..... 22
Outline Dimensions....................................................................... 23
Ordering Guide .......................................................................... 24
REVISION HISTORY
10/2017—Rev. F to Rev. G
Changes to Table 1.............................................................................1
Changes to AC Accuracy Parameter, Table 2 ................................3
Changed nA to μA, Standby Current Parameter, Unit Column,
Table 3 .................................................................................................4
Changes to Table 8.......................................................................... 16
Changes to Power Supply Section................................................ 17
Updated Outline Dimensions....................................................... 22
Changes to Features Section and Table 1 ...................................... 1
Moved Typical Application Circuit Section and Figure 1........... 3
Changes to Figure 5.......................................................................... 9
Updated Outline Dimensions....................................................... 23
Changes to Ordering Guide .......................................................... 24
4/2016—Rev. E to Rev. F
Changed AD7988-x to AD7988-1/AD7988-5........... Throughout
Changes to Table 1............................................................................ 1
Changes to Table 2............................................................................ 3
Changes to Table 3............................................................................ 4
Changes to Table 4............................................................................ 5
Added Table 5: Renumbered Sequentially .................................... 6
Changes to Figure 29...................................................................... 14
Changes to Table 9.......................................................................... 16
Changes to Voltage Reference Input Section .............................. 17
Changes to Figure 35...................................................................... 18
Changes to Figure 37...................................................................... 20
Changes to Ordering Guide .......................................................... 23
8/2013—Rev. C to Rev. D
Changes to Features Section ............................................................1
Changes to Table 3.............................................................................4
Updated Outline Dimensions....................................................... 22
Changes to Ordering Guide.......................................................... 23
8/2012—Rev. B to Rev. C
Changes to Ordering Guide.......................................................... 23
5/2012—Rev. A to Rev. B
Changes to Table 3.............................................................................4
Updated Outline Dimensions....................................................... 22
8/2014—Rev. D to Rev. E
2/2012—Rev. 0 to Rev. A
Deleted QFN .................................................................. Throughout
Changed Typical Application Diagram Section to Typical
Application Circuit Section............................................................. 1
Changes to Features Section............................................................ 1
Added Patent Note, Note 1.............................................................. 1
Added LFCSP Thermal Impedance Values....................................7
Updated Outline Dimensions....................................................... 23
Changes to Ordering Guide.......................................................... 23
2/2012—Revision 0: Initial Version
Rev. G | Page 2 of 24
Data Sheet
AD7988-1/AD7988-5
TYPICAL APPLICATION CIRCUIT
2.5V TO 5V 2.5V
VIO
SDI
1.8V TO 5.5V
REF VDD
0V TO V
REF
IN+ AD7988-1/ SCK
3- OR 4-WIRE INTERFACE
(SPI, DAISY CHAIN, CS)
IN– AD7988-5
SDO
GND
CNV
Figure 1.
Rev. G | Page 3 of 24
AD7988-1/AD7988-5
Data Sheet
SPECIFICATIONS
VDD = 2.5 V, VIO = 1.71 V to 5.5 V, VREF = 5 V, TA = –40°C to +125°C, unless otherwise noted.
Table 2.
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
RESOLUTION
16
Bits
ANALOG INPUT
Voltage Range
Absolute Input Voltage
IN+ − IN−
IN+
IN−
0
−0.1
−0.1
VREF
VREF + 0.1
+0.1
V
V
V
Analog Input CMRR
Leakage Current at 25°C
Input Impedance
fIN = 1 kHz
Acquisition phase
60
1
dB
nA
See the Analog Inputs section
ACCURACY
No Missing Codes
Differential Linearity Error
16
−0.9
Bits
VREF = 5 V
VREF = 2.5 V
VREF = 5 V
VREF = 2.5 V
VREF = 5 V
VREF = 2.5 V
0.4
0.55
0.6
0.65
0.6
1.0
2
0.35
0.08
0.54
0.1
+0.9
LSB1
LSB1
LSB1
LSB1
LSB1
LSB1
LSB1
ppm/°C
mV
Integral Linearity Error
Transition Noise
−1.25
−0.5
+1.25
2
Gain Error, TMIN to TMAX
Gain Error Temperature Drift
Zero Error, TMIN to TMAX
Zero Temperature Drift
Power Supply Sensitivity
THROUGHPUT
2
+0.5
ppm/°C
LSB1
VDD = 2.5 V 5%
AD7988-1
Conversion Rate
Transient Response
AD7988-5
Conversion Rate
Transient Response
AC ACCURACY
0
0
100
500
kSPS
ns
Full-scale step
Full-scale step
500
400
kSPS
ns
Dynamic Range
VREF = 5 V
VREF = 2.5 V
fO = 10 kSPS
fIN = 10 kHz, VREF = 5 V
fIN = 10 kHz, VREF = 2.5 V
fIN = 10 kHz
fIN = 10 kHz
fIN = 10 kHz, VREF = 5 V
fIN = 10 kHz, VREF = 2.5 V
92
87
dB3
dB3
dB3
dB3
dB3
dB3
dB3
dB3
dB3
Oversampled Dynamic Range
Signal-to-Noise Ratio, SNR
111
91.5
87
−110
−114
91
90
Spurious-Free Dynamic Range, SFDR
Total Harmonic Distortion, THD
Signal-to-(Noise + Distortion), SINAD
86.5
1 LSB means least significant bit. With the 5 V input range, 1 LSB is 76.3 µV.
2 See the Terminology section. These specifications include full temperature range variation, but not the error contribution from the external reference.
3 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.
Rev. G | Page 4 of 24
Data Sheet
AD7988-1/AD7988-5
VDD = 2.5 V, VIO = 1.71 V to 5.5 V, VREF = 5 V, TA = –40°C to +125°C, unless otherwise noted.
Table 3.
Parameter
REFERENCE
Voltage Range
Load Current
SAMPLING DYNAMICS
−3 dB Input Bandwidth
Aperture Delay
DIGITAL INPUTS
Logic Levels
VIL
Test Conditions/Comments
VREF = 5 V
Min
Typ
Max
Unit
2.4
5.1
V
µA
250
10
2.0
MHz
ns
VDD = 2.5 V
VIO > 3 V
VIO > 3 V
VIO ≤ 3 V
VIO ≤ 3 V
–0.3
0.7 × VIO
–0.3
0.9 × VIO
−1
−1
0.3 × VIO
VIO + 0.3
0.1 × VIO
VIO + 0.3
+1
V
V
V
V
µA
µA
VIH
VIL
VIH
IIL
IIH
+1
DIGITAL OUTPUTS
Data Format
Pipeline Delay
Serial 16 bits straight binary
Conversion results available immediately
after completed conversion
VOL
VOH
ISINK = 500 µA
ISOURCE = −500 µA
0.4
V
V
VIO − 0.3
POWER SUPPLIES
VDD
VIO
2.375
1.71
2.5
2.625
5.5
V
V
Standby Current1, 2
AD7988-1 Power Dissipation
Total
VDD and VIO = 2.5 V, 25°C
VDD = 2.625 V, VREF = 5 V, VIO = 3 V
10 kSPS throughput
0.35
µA
70
700
µW
µW
mW
µW
µW
µW
100 kSPS throughput
1
5
VDD Only
REF Only
VIO Only
AD7988-5 Power Dissipation
Total
VDD Only
400
170
130
VDD = 2.625 V, VREF = 5 V, VIO = 3 V
500 kSPS throughput
3.5
2
mW
mW
REF Only
VIO Only
Energy per Conversion
TEMPERATURE RANGE
Specified Performance
0.85
0.65
7.0
mW
mW
nJ/sample
TMIN to TMAX
−40
+125
°C
1 With all digital inputs forced to VIO or GND as required.
2 During the acquisition phase.
Rev. G | Page 5 of 24
AD7988-1/AD7988-5
Data Sheet
TIMING SPECIFICATIONS
VDD = 2.37 V to 2.63 V, VIO = 3.3 V to 5.5 V, −40°C to +125°C unless otherwise stated. See Figure 2 and Figure 3 for load conditions.
Table 4.
Parameter
Symbol
Min
Typ
Max
Unit
AD7988-1
Throughput Rate
Conversion Time: CNV Rising Edge to Data Available
Acquisition Time
Time Between Conversions
100
9.5
kHz
μs
ns
tCONV
tACQ
tCYC
500
10
μs
AD7988-5
Throughput Rate
500
kHz
Conversion Time: CNV Rising Edge to Data Available
tCONV
B Grade
C Grade
1.6
1.2
µs
µs
Acquisition Time
tACQ
B Grade
C Grade
Time Between Conversions
CNV Pulse Width (CS Mode)
SCK Period (CS Mode)
400
800
2
ns
ns
μs
ns
tCYC
tCNVH
tSCK
500
VIO Above 4.5 V
VIO Above 3 V
VIO Above 2.7 V
VIO Above 2.3 V
10.5
12
13
ns
ns
ns
ns
15
SCK Period (Chain Mode)
tSCK
VIO Above 4.5 V
VIO Above 3 V
VIO Above 2.7 V
VIO Above 2.3 V
SCK Low Time
SCK High Time
SCK Falling Edge to Data Remains Valid
SCK Falling Edge to Data Valid Delay
VIO Above 4.5 V
11.5
13
14
16
4.5
4.5
3
ns
ns
ns
ns
ns
ns
ns
tSCKL
tSCKH
tHSDO
tDSDO
9.5
11
12
14
ns
ns
ns
ns
VIO Above 3 V
VIO Above 2.7 V
VIO Above 2.3 V
CNV or SDI Low to SDO D15 MSB Valid (CS Mode)
VIO Above 3 V
VIO Above 2.3V
tEN
10
15
20
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
CNV or SDI High or Last SCK Falling Edge to SDO High Impedance (CS Mode)
SDI Valid Setup Time from CNV Rising Edge
SDI Valid Hold Time from CNV Rising Edge (CS Mode)
SDI Valid Hold Time from CNV Rising Edge (Chain Mode)
SCK Valid Setup Time from CNV Rising Edge (Chain Mode)
SCK Valid Hold Time from CNV Rising Edge (Chain Mode)
SDI Valid Setup Time from SCK Falling Edge (Chain Mode)
SDI Valid Hold Time from SCK Falling Edge (Chain Mode)
tDIS
tSSDICNV
tHSDICNV
tHSDICNV
tSSCKCNV
tHSCKCNV
tSSDISCK
tHSDISCK
5
2
0
5
5
2
3
Rev. G | Page 6 of 24
Data Sheet
AD7988-1/AD7988-5
VDD = 2.37 V to 2.63 V, VIO = 1.71 V to 3.3 V, −40°C to +125°C unless otherwise stated. See Figure 2 and Figure 3 for load conditions.
Table 5.
Parameter
Symbol
Min
Typ
Max
Unit
AD7988-1
Throughput Rate
Conversion Time: CNV Rising Edge to Data Available
Acquisition Time
100
9.5
kHz
μs
ns
tCONV
tACQ
tCYC
500
10
Time Between Conversions
μs
AD7988-5
Throughput Rate
500
kHz
Conversion Time: CNV Rising Edge to Data Available
B Grade
C Grade
tCONV
1.6
1.2
μs
μs
Acquisition Time
tACQ
B Grade
C Grade
Time Between Conversions
CNV Pulse Width (CS Mode)
400
800
2
500
22
23
6
ns
ns
μs
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
tCYC
tCNVH
tSCK
SCK Period (CS Mode)
SCK Period (Chain Mode)
SCK Low Time
SCK High Time
tSCK
tSCKL
tSCKH
tHSDO
tDSDO
tEN
6
3
SCK Falling Edge to Data Remains Valid
SCK Falling Edge to Data Valid Delay
CNV or SDI Low to SDO D15 MSB Valid (CS Mode)
CNV or SDI High or Last SCK Falling Edge to SDO High Impedance (CS Mode)
SDI Valid Setup Time from CNV Rising Edge
SDI Valid Hold Time from CNV Rising Edge (CS Mode)
SDI Valid Hold Time from CNV Rising Edge (Chain Mode)
SCK Valid Setup Time from CNV Rising Edge (Chain Mode)
SCK Valid Hold Time from CNV Rising Edge (Chain Mode)
SDI Valid Setup Time from SCK Falling Edge (Chain Mode)
SDI Valid Hold Time from SCK Falling Edge (Chain Mode)
14
18
21
40
20
tDIS
tSSDICNV
tHSDICNV
tHSDICNV
tSSCKCNV
tHSCKCNV
tSSDISCK
tHSDISCK
5
10
0
5
5
2
3
500µA
I
OL
1.4V
TO SDO
C
L
20pF
500µA
I
OH
Figure 2. Load Circuit for Digital Interface Timing
1
Y% VIO
1
X% VIO
tDELAY
tDELAY
2
2
V
V
V
IH
IH
2
2
V
IL
IL
1
2
FOR VIO ≤ 3.0V, X = 90 AND Y = 10; FOR VIO > 3.0V X = 70, AND Y = 30.
MINIMUM V AND MAXIMUM V USED. SEE DIGITAL INPUTS
IH
IL
SPECIFICATIONS IN TABLE 3.
Figure 3. Voltage Levels for Timing
Rev. G | Page 7 of 24
AD7988-1/AD7988-5
Data Sheet
ABSOLUTE MAXIMUM RATINGS
Table 6.
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
Parameter
Rating
Analog Inputs
IN+,1 IN−1 to GND
Supply Voltage
REF, VIO to GND
VDD to GND
VDD to VIO
−0.3 V to VREF + 0.3 V or 130 mA
−0.3 V to +6 V
−0.3 V to +3 V
+3 V to −6 V
Digital Inputs to GND
Digital Outputs to GND
Storage Temperature Range
Junction Temperature
θJA Thermal Impedance
10-Lead MSOP
−0.3 V to VIO + 0.3 V
−0.3 V to VIO + 0.3 V
−65°C to +125°C
150°C
ESD CAUTION
200°C/W
80°C/W
10-Lead LFCSP
θJC Thermal Impedance
10-Lead MSOP
44°C/W
10-Lead LFCSP
15°C/W
Reflow Soldering
JEDEC Standard (J-STD-020)
1 See the Analog Inputs section.
Rev. G | Page 8 of 24
Data Sheet
AD7988-1/AD7988-5
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
REF
VDD
IN+
1
2
3
4
5
10 VIO
9
8
7
6
SDI
AD7988-1/
SCK
SDO
CNV
REF
VDD
IN+
1
2
3
4
5
10 VIO
AD7988-5
TOP VIEW
AD7988-1/
AD7988-5
TOP VIEW
(Not to Scale)
9
8
7
6
SDI
IN–
(Not to Scale)
SCK
SDO
CNV
GND
IN–
NOTES
GND
1. THE EXPOSED PAD CAN BE CONNECTED TO GND.
Figure 4. 10-Lead MSOP Pin Configuration
Figure 5. 10-Lead LFCSP Pin Configuration
Table 7. Pin Function Descriptions
Pin No. Mnemonic Type1 Description
1
REF
AI
Reference Input Voltage. The VREF range is from 2.4 V to 5.1 V. It is referred to the GND pin. The GND pin
should be decoupled closely to the REF pin with a 10 μF capacitor.
2
3
VDD
IN+
P
AI
Power Supply.
Analog Input. It is referred to IN−. The voltage range, for example, the difference between IN+ and IN−, is
0 V to VREF
.
4
5
6
IN−
GND
CNV
AI
P
DI
Analog Input Ground Sense. Connect to the analog ground plane or to a remote sense ground.
Power Supply Ground.
Convert Input. This input has multiple functions. On its leading edge, it initiates the conversions and
selects the interface mode of the part: chain mode or CS mode. In CS mode, the SDO pin is enabled when
CNV is low. In chain mode, the data should be read when CNV is high.
7
8
9
SDO
SCK
SDI
DO
DI
DI
Serial Data Output. The conversion result is output on this pin. It is synchronized to SCK.
Serial Data Clock Input. When the part is selected, the conversion result is shifted out by this clock.
Serial Data Input. This input provides multiple features. It selects the interface mode of the ADC as
follows:
Chain mode is selected if this pin is low during the CNV rising edge. In this mode, SDI is used as a data
input to daisy-chain the conversion results of two or more ADCs onto a single SDO line. The digital data
level on SDI is output on SDO with a delay of 16 SCK cycles.
CS mode is selected if SDI is high during the CNV rising edge. In this mode, either SDI or CNV can enable
the serial output signals when low.
10
VIO
EP
P
Input/Output Interface Digital Power. Nominally at the same supply as the host interface (1.8 V, 2.5 V, 3 V,
or 5 V).
Exposed Pad. The exposed pad can be connected to GND.
1AI = analog input, DI = digital input, DO = digital output, and P = power.
Rev. G | Page 9 of 24
AD7988-1/AD7988-5
Data Sheet
TERMINOLOGY
Effective Resolution
Effective resolution is calculated as
Integral Nonlinearity Error (INL)
INL 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 (see Figure 30).
Effective Resolution = log2(2N/RMS Input Noise)
and is expressed in bits.
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 dB.
Differential Nonlinearity Error (DNL)
In an ideal ADC, code transitions are 1 LSB apart. DNL is the
maximum deviation from this ideal value. It is often specified in
terms of resolution for which no missing codes are guaranteed.
Dynamic Range
Dynamic range is the ratio of the rms value of the full scale to
the total rms noise measured with the inputs shorted together.
The value for dynamic range is expressed in dB. It is measured
with a signal at −60 dBFS to include all noise sources and DNL
artifacts.
Offset Error
The first transition should occur at a level ½ LSB above analog
ground (38.1 µV for the 0 V to 5 V range). The offset error is
the deviation of the actual transition from that point.
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 dB.
Gain Error
The last transition (from 111 … 10 to 111 … 11) should
occur for an analog voltage 1½ LSB below the nominal full
scale (4.999886 V for the 0 V to 5 V range). The gain error is
the deviation of the actual level of the last transition from the
ideal level after the offset is adjusted out.
Signal-to-(Noise + Distortion) Ratio (SINAD)
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 dB.
Spurious-Free Dynamic Range (SFDR)
SFDR is the difference, in decibels (dB), between the rms
amplitude of the input signal and the peak spurious signal.
Aperture Delay
Effective Number of Bits (ENOB)
Aperture delay is the measure of the acquisition performance. It
is the time between the rising edge of the CNV input and when
the input signal is held for a conversion.
ENOB is a measurement of the resolution with a sine wave
input. It is related to SINAD by the following formula:
ENOB = (SINADdB − 1.76)/6.02
Transient Response
and is expressed in bits.
Transient response is the time required for the ADC to
accurately acquire its input after a full-scale step function is
applied.
Noise-Free Code Resolution
Noise-free code resolution is the number of bits beyond which
it is impossible to distinctly resolve individual codes. It is
calculated as
Noise-Free Code Resolution = log2(2N/Peak-to-Peak Noise)
and is expressed in bits.
Rev. G | Page 10 of 24
Data Sheet
AD7988-1/AD7988-5
TYPICAL PERFORMANCE CHARACTERISTICS
VDD = 2.5 V, VREF = 5.0 V, VIO = 3.3 V, unless otherwise noted.
0
0
–20
fS = 500kSPS
fS = 100kSPS
fIN = 10kHz
SNR = 86.7dB
THD = –110.4dB
SFDR = 103.9dB
SINAD = 86.6dB
fIN = 10kHz
–20
–40
SNR = 91.17dB
THD = –113.63dB
SFDR = 110.30dB
SINAD = 91.15dB
–40
–60
–60
–80
–80
–100
–120
–140
–160
–180
–100
–120
–140
–160
–180
0
50
100
150
200
250
0
10
20
30
40
50
FREQUENCY (kHz)
FREQUENCY (kHz)
Figure 6. AD7988-5 FFT Plot, VREF = 5 V
Figure 9. AD7988-1 FFT Plot, VREF = 2.5 V
0
–20
1.25
1.00
0.75
0.50
0.25
0
POSITIVE INL: +0.40 LSB
NEGATIVE INL: –0.35 LSB
fS = 500kSPS
fIN = 10kHz
SNR = 86.8dB
THD = –111.4dB
SFDR = 105.9dB
SINAD = 86.8dB
–40
–60
–80
–100
–120
–140
–160
–180
–0.25
–0.50
–0.75
–1.00
–1.25
0
50
100
150
200
250
0
16384
32768
CODE
49152
65536
FREQUENCY (kHz)
Figure 10. Integral Nonlinearity vs. Code, VREF = 5 V
Figure 7. AD7988-5 FFT Plot, VREF = 2.5 V
0
1.25
1.00
0.75
0.50
0.25
0
POSITIVE INL: +0.45 LSB
NEGATIVE INL: –0.29 LSB
fS = 100kSPS
fIN = 10kHz
–20
–40
SNR = 91.09dB
THD = –113.12dB
SFDR = 110.30dB
SINAD = 91.05dB
–60
–80
–100
–120
–140
–160
–180
–0.25
–0.50
–0.75
–1.00
–1.25
0
10
20
30
40
50
0
16384
32768
CODE
49152
65536
FREQUENCY (kHz)
Figure 11. Integral Nonlinearity vs. Code, VREF = 2.5 V
Figure 8. AD7988-1 FFT Plot, VREF = 5 V
Rev. G | Page 11 of 24
AD7988-1/AD7988-5
Data Sheet
1.00
0.75
0.50
0.25
0
60k
50k
40k
30k
20k
10k
0
POSITIVE INL: +0.18 LSB
NEGATIVE INL: –0.21 LSB
50970
45198
–0.25
–0.50
–0.75
–1.00
18848
12424
1217
2290
94
30
0
0
1
0
0
7FFA 7FFB 7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004 8005 8006
CODE IN HEX
0
16384
32768
CODE
49152
65536
Figure 15. Histogram of a DC Input at the Code Transition, VREF = 2.5 V
Figure 12. Differential Nonlinearity vs. Code, VREF = 5 V
100
95
16
15
14
1.00
0.75
0.50
0.25
0
POSITIVE INL: +0.25 LSB
NEGATIVE INL: –0.22 LSB
SNR
SINAD
ENOB
90
–0.25
–0.50
–0.75
–1.00
85
80
13
12
2.25
2.75
3.25
3.75
4.25
4.75
5.25
0
16384
32768
CODE
49152
65536
REFERENCE VOLTAGE (V)
Figure 16. SNR, SINAD, and ENOB vs. Reference Voltage
Figure 13. Differential Nonlinearity vs. Code, VREF = 2.5 V
60k
180k
160k
140k
120k
100k
80k
60k
40k
20k
0
162595
53412
50k
40k
30k
20k
10k
0
37417
31540
52720
42731
7285
5807
590
512
19
1291
852
11
0
0
0
0
29
0
0
22
2
0
0
0
7FFA 7FFB 7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004 8005 8006
CODE IN HEX
8003 8004 8005 8006 8007 8008 8009 800A 800B 800C 800D 800E 800F
CODE IN HEX
Figure 17. Histogram of a DC Input at the Code Center, VREF = 2.5 V
Figure 14. Histogram of a DC Input at the Code Center, VREF = 5 V
Rev. G | Page 12 of 24
Data Sheet
AD7988-1/AD7988-5
95
93
91
89
87
85
95
94
93
92
91
90
89
88
87
86
85
–55
–35
–15
5
25
45
65
85
105
125
–10
–9
–8
–7
–6
–5
–4
–3
–2
–1
0
TEMPERATURE (°C)
INPUT LEVEL (dB OF FULL SCALE)
Figure 21. SNR vs. Temperature
Figure 18. SNR vs. Input Level
0.7
0.6
0.5
0.4
0.3
0.2
–95
–100
–105
–110
–115
115
110
105
100
95
I
VDD
SFDR
I
REF
THD
I
VIO
0.1
0
–120
–125
90
85
2.375
2.425
2.475
2.525
2.575
2.625
2.25
2.75
3.25
3.75
4.25
4.75
5.25
VDD VOLTAGE (V)
REFERENCE VOLTAGE (V)
Figure 22. Operating Currents vs. Supply (AD7988-5)
Figure 19. THD, SFDR vs. Reference Voltage
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0
100
95
90
85
80
I
VDD
I
REF
I
VIO
2.375
2.425
2.475
2.525
2.575
2.625
10
100
1k
VDD VOLTAGE (V)
FREQUENCY (kHz)
Figure 23. Operating Currents vs. Supply (AD7988-1)
Figure 20. SINAD vs. Frequency
Rev. G | Page 13 of 24
AD7988-1/AD7988-5
Data Sheet
–85
0.14
0.12
0.10
008
I
VDD
–90
–95
–100
–105
–110
–115
–120
–125
0.06
I
REF
0.04
0.02
0
I
VIO
–55
–35
–15
5
25
45
65
85
105
125
10
100
1k
125
125
TEMPERATURE (°C)
FREQUENCY (kHz)
Figure 24. THD vs. Frequency
Figure 27. Operating Currents vs. Temperature (AD7988-1)
8
–110
7
6
5
4
3
2
1
–112
–114
–116
–118
–120
I
+ I
VIO
VDD
0
–55
–35
–15
5
25
45
65
85
105
125
–55
–35
–15
5
25
45
65
85
105
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 25. THD vs. Temperature
Figure 28. Power-Down Currents vs. Temperature
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
I
VDD
I
REF
I
VIO
–55
–35
–15
5
25
45
65
85
105
TEMPERATURE (°C)
Figure 26. Operating Currents vs. Temperature (AD7988-5)
Rev. G | Page 14 of 24
Data Sheet
AD7988-1/AD7988-5
THEORY OF OPERATION
IN+
SWITCHES CONTROL
SW+
MSB
LSB
32,768C 16,384C
4C
4C
2C
2C
C
C
C
C
REF
CONTROL
LOGIC
COMP
OUTPUT CODE
GND
32,768C 16,384C
MSB
LSB
SW–
CNV
IN–
Figure 29. ADC Simplified Schematic
During the acquisition phase, terminals of the array tied to the
comparator’s input are connected to GND via SW+ and SW−.
All independent switches are connected to the analog inputs.
Therefore, the capacitor arrays are used as sampling capacitors
and acquire the analog signal on the IN+ and IN− inputs. When
the acquisition phase is completed and the CNV input goes high, a
conversion phase is initiated. 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 GND input.
Therefore, the differential voltage between the IN+ and IN−
inputs captured at the end of the acquisition phase are applied
to the comparator inputs, causing the comparator to become
unbalanced. By switching each element of the capacitor array
between GND and REF, the comparator input varies by binary
weighted voltage steps (VREF/2, VREF/4 … VREF/65,536). The
control logic toggles these switches, starting with the MSB, to
bring the comparator back into a balanced condition. After the
completion of this process, the part returns to the acquisition phase
and the control logic generates the ADC output code.
CIRCUIT INFORMATION
The AD7988-1/AD7988-5 devices are fast, low power, single-
supply, precise 16-bit ADCs that use a successive approximation
architecture.
The AD7988-1 is capable of converting 100,000 samples per
second (100 kSPS), whereas the AD7988-5 is capable of a
throughput of 500 kSPS, and they power down between
conversions. When operating at 10 kSPS, for example, the
ADC consumes 70 µW typically, ideal for battery-powered
applications.
The AD7988-1/AD7988-5 provide the user with on-chip track-
and-hold and does not exhibit any pipeline delay or latency,
making it ideal for multiple multiplexed channel applications.
The AD7988-1/AD7988-5 can be interfaced to any 1.8 V to 5 V
digital logic family. It is housed in a 10-lead MSOP or a tiny 10-
lead LFCSP that combines space savings and allows flexible
configurations.
CONVERTER OPERATION
Because the AD7988-1/AD7988-5 have an on-board conversion
clock, the serial clock, SCK, is not required for the conversion
process.
The AD7988-1/AD7988-5 are successive approximation ADCs
based on a charge redistribution DAC. Figure 29 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.
Rev. G | Page 15 of 24
AD7988-1/AD7988-5
Data Sheet
Transfer Functions
Table 8. Output Codes and Ideal Input Voltages
Analog Input
The ideal transfer characteristic for the AD7988-1/AD7988-5 is
shown in Figure 30 and Table 8.
Description
VREF = 5 V
Digital Output Code (Hex)
FSR – 1 LSB
4.999924 V
FFFF1
8001
8000
7FFF
0001
00002
Midscale + 1 LSB 2.500076 V
Midscale 2.5 V
Midscale – 1 LSB 2.499924 V
–FSR + 1 LSB
–FSR
111 ... 111
111 ... 110
111 ... 101
76.3 µV
0 V
1 This is also the code for an overranged analog input (VIN+ − VIN− above VREF − VGND).
2 This is also the code for an underranged analog input (VIN+ − VIN− below VGND).
TYPICAL CONNECTION DIAGRAM
Figure 31 shows an example of the recommended connection
diagram for the AD7988-1/AD7988-5 when multiple supplies
are available.
000 ... 010
000 ... 001
000 ... 000
–FSR
–FSR + 1LSB
+FSR – 1 LSB
–FSR + 0.5LSB
+FSR – 1.5 LSB
ANALOG INPUT
Figure 30. ADC Ideal Transfer Function
1
V+
REF
2.5V
2
10µF
100nF
V+
1.8V TO 5.5V
100nF
20Ω
REF
VDD
VIO
0V TO V
REF
3
IN+
IN–
SDI
SCK
SDO
CNV
2.7nF
AD7988-1/
AD7988-5
V–
5
3- OR 4-WIRE INTERFACE
4
GND
1
2
3
4
5
SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
SEE THE DRIVER AMPLIFIER CHOICE SECTION.
OPTIONAL FILTER. SEE THE ANALOG INPUTS SECTION.
SEE THE DIGITAL INTERFACE SECTION FOR THE MOST CONVENIENT INTERFACE MODE.
C
REF
Figure 31. Typical Application Diagram with Multiple Supplies
Rev. G | Page 16 of 24
Data Sheet
AD7988-1/AD7988-5
ANALOG INPUTS
DRIVER AMPLIFIER CHOICE
Figure 32 shows an equivalent circuit of the input structure of
the AD7988-1/AD7988-5.
Although the AD7988-1/AD7988-5 are easy to drive, the driver
amplifier needs to meet the following requirements:
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 these diodes to become forward-
biased and start conducting current. These diodes can handle a
forward-biased current of 130 mA maximum. For instance,
these conditions may eventually occur when the input buffer’s
supplies are different from VDD. In such a case (for example, an
input buffer with a short circuit), the current limitation can be
used to protect the part.
•
The noise generated by the driver amplifier must be kept as
low as possible to preserve the SNR and transition noise
performance of the AD7988-1/AD7988-5. The noise
coming from the driver is filtered by the AD7988-1/
AD7988-5 analog input circuit’s one-pole, low-pass filter
made by RIN and CIN or by the external filter, if one is used.
Because the typical noise of the AD7988-1/AD7988-5 is
47.3 µV rms, the SNR degradation due to the amplifier is
47.3
REF
SNRLOSS = 20 log
π
47.32 + f−3dB (NeN )2
D1
C
2
IN
R
IN
IN+
OR IN–
•
where:
–3dB is the input bandwidth in MHz of the AD7988-1/
C
D2
PIN
f
GND
AD7988-5 (10 MHz) or the cutoff frequency of the input
filter, if one is used.
Figure 32. Equivalent Analog Input Circuit
N is the noise gain of the amplifier (for example, 1 in buffer
configuration).
eN is the equivalent input noise voltage of the op amp, in
The analog input structure allows the sampling of the true
differential signal between IN+ and IN−. By using these
differential inputs, signals common to both inputs are rejected.
nV/√Hz.
During the acquisition phase, 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
•
•
For ac applications, the driver should have a THD
performance commensurate with the AD7988-1/AD7988-5.
For multichannel multiplexed applications, the driver ampli-
fier and the AD7988-1/AD7988-5 analog input circuit must
settle for a full-scale step onto the capacitor array at a
16-bit level (0.0015%, 15 ppm). In the amplifier data sheet,
settling at 0.1% to 0.01% is more commonly specified. This
may differ significantly from the settling time at a 16-bit
level and should be verified prior to driver selection.
RIN and CIN. CPIN is primarily the pin capacitance. RIN is typically
400 Ω and is a lumped component made up of serial resistors
and the on resistance of the switches. CIN is typically 30 pF and
is mainly 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
reduces undesirable aliasing effects and limits the noise.
Table 9. Recommended Driver Amplifiers1
When the source impedance of the driving circuit is low, the
AD7988-1/AD7988-5 can be driven directly. Large source
impedances significantly affect the ac performance, especially
THD. The dc performances are less sensitive to the input
impedance. 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.
Amplifier
Typical Application
ADA4805-1
ADA4807-1
ADA4627-1
ADA4522-1
ADA4500-2
Low noise, small size, and low power
Very low noise and high frequency
Precision, low noise, and low input bias
Precision, zero-drift, and EMI enhanced
Precision, RRIO, and zero input crossover
distortion
1 For the latest recommended drivers, see the product recommendations
listed on the product webpage.
Rev. G | Page 17 of 24
AD7988-1/AD7988-5
Data Sheet
The AD7988-1/AD7988-5 powers down automatically at the end
of each conversion phase.
VOLTAGE REFERENCE INPUT
The AD7988-1/AD7988-5 voltage reference input, REF, has a
dynamic input impedance and must therefore be driven by a
low impedance source with efficient decoupling between the
REF and GND pins, as explained in the Layout section.
DIGITAL INTERFACE
Although the AD7988-1/AD7988-5 have a reduced number of
pins, it offers flexibility in its serial interface modes.
When REF is driven by a very low impedance source, for example,
a reference buffer using the AD8031 or the ADA4805-1, a
ceramic chip capacitor is appropriate for optimum
performance.
CS
The AD7988-1/AD7988-5, when in
mode, is compatible with
SPI, QSPI™, and digital hosts. This interface can use either a 3-wire
or 4-wire interface. A 3-wire interface using the CNV, SCK, and
SDO signals minimizes wiring connections and is useful, for
instance, in isolated applications. A 4-wire interface using the
SDI, CNV, SCK, and SDO signals allows CNV, which initiates
the conversions, to be independent of the readback timing
(SDI). This is useful in low jitter sampling or simultaneous
sampling applications.
If an unbuffered reference voltage is used, the decoupling value
depends on the reference used. For example, a 22 µF (X5R,
1206 size) ceramic chip capacitor is appropriate for optimum
performance using a low temperature drift ADR435 reference.
If desired, a reference-decoupling capacitor value as small as
2.2 µF can be used with a minimal impact on performance,
especially DNL.
The AD7988-1/AD7988-5, when in chain mode, provides a
daisy-chain feature using the SDI input for cascading multiple
ADCs on a single data line, similar to a shift register.
Regardless, there is no need for an additional lower value ceramic
decoupling capacitor (for example, 100 nF) between the REF
and GND pins.
The mode in which the part operates depends on the SDI level
CS
when the CNV rising edge occurs.
mode is selected if SDI is
high, and chain mode is selected if SDI is low. The SDI hold
time is such that when SDI and CNV are connected together,
the chain mode is selected.
POWER SUPPLY
The AD7988-1/AD7988-5 use two power supply pins: a core
supply, VDD, and a digital input/output interface supply, VIO.
VIO allows direct interface with any logic between 1.8 V and
5.0 V. To reduce the number of supplies needed, VIO and VDD
can be tied together. The AD7988-1/AD7988-5 are independent
of power supply sequencing between VIO and VDD. Additionally,
it is very insensitive to power supply variations over a wide
frequency range, as shown in Figure 33.
The user must time out the maximum conversion time prior to
readback.
80
75
70
65
60
55
1
10
100
1k
FREQUENCY (kHz)
Figure 33. PSRR vs. Frequency
Rev. G | Page 18 of 24
Data Sheet
AD7988-1/AD7988-5
When CNV goes low, the MSB is output onto SDO. The remaining
data bits are then clocked by subsequent SCK falling edges. The
data is valid on both SCK edges. Although the rising edge can
be used to capture the data, a digital host using the SCK falling
edge allows a faster reading rate, provided that it has an acceptable
hold time. After the 16th SCK falling edge or when CNV goes
high, whichever is earlier, SDO returns to high impedance.
CS MODE, 3-WIRE
This mode is typically used when a single AD7988-1or AD7988-5
is connected to an SPI-compatible digital host. The connection
diagram is shown in Figure 34, and the corresponding timing is
given in Figure 35.
With SDI tied to VIO, a rising edge on CNV initiates a conver-
CS
sion, selects the
mode, and forces SDO to high impedance.
When the conversion is complete, the AD7988-1/AD7988-5
enter the acquisition phase and powers down.
CONVERT
DIGITAL HOST
DATA IN
CNV
VIO
AD7988-1/
AD7988-5
SDI
SDO
SCK
CLK
CS
Figure 34. 3-Wire Mode Connection Diagram
SDI = 1
tCYC
tCNVH
CNV
tCONV
tACQ
ACQUISITION
CONVERSION
ACQUISITION
tSCK
tSCKL
1
2
3
14
15
16
SCK
SDO
tHSDO
tSCKH
tDIS
tEN
tDSDO
D15
D14
D13
D1
D0
CS
Figure 35. 3-Wire Mode Serial Interface Timing (SDI High)
Rev. G | Page 19 of 24
AD7988-1/AD7988-5
Data Sheet
When the conversion is complete, the AD7988-1/AD7988-5
CS MODE 4-WIRE
enter the acquisition phase and powers down. Each ADC result
can be read by bringing its SDI input low, which consequently
outputs the MSB onto SDO. The remaining data bits are then
clocked by subsequent SCK falling edges. The data is valid on
both SCK edges. Although the rising edge can be used to capture
the data, a digital host using the SCK falling edge allows a faster
reading rate, provided that it has an acceptable hold time. After
the 16th SCK falling edge or when SDI goes high, whichever is
earlier, SDO returns to high impedance and another AD7988-1
or AD7988-5 can be read.
This mode is typically used when multiple AD7988-1/AD7988-5
devices are connected to an SPI-compatible digital host.
A connection diagram example using the AD7988-1/AD7988-5
devices are shown in Figure 36, and the corresponding timing is
given in Figure 37.
With SDI high, a rising edge on CNV initiates a conversion,
CS
selects the
mode, and forces SDO to high impedance. In this
mode, CNV must be held high during the conversion phase and
the subsequent data readback (if SDI and CNV are low, SDO is
driven low). Prior to the minimum conversion time, SDI can be
used to select other SPI devices, such as analog multiplexers,
but SDI must be returned high before the minimum conversion
time elapses and then held high for the maximum conversion time.
CS2
CS1
CONVERT
CNV
CNV
DIGITAL HOST
AD7988-1/
AD7988-5
AD7988-1/
AD7988-5
SDI
SDO
SDI
SDO
SCK
SCK
DATA IN
CLK
CS
Figure 36. 4-Wire Mode Connection Diagram
tCYC
CNV
tCONV
tACQ
ACQUISITION
tSSDICNV
CONVERSION
ACQUISITION
SDI (CS1)
tHSDICNV
SDI (CS2)
SCK
tSCK
tSCKL
1
2
3
14
15
16
17
18
30
31
32
tHSDO
tSCKH
tEN
tDIS
tDSDO
SDO
D15
D14
D13
D1
D0
D15
D14
D1
D0
CS
Figure 37. 4-Wire Mode Serial Interface Timing
Rev. G | Page 20 of 24
Data Sheet
AD7988-1/AD7988-5
phase and the subsequent data readback. When the conversion
is complete, the MSB is output onto SDO and the AD7988-1/
AD7988-5 enter the acquisition phase and power down. The
remaining data bits stored in the internal shift register are
clocked by subsequent SCK falling edges. For each ADC, SDI
feeds the input of the internal shift register and is clocked by the
SCK falling edge. Each ADC in the chain outputs its data MSB
first, and 16 × N clocks are required to read back the N ADCs.
The data is valid on both SCK edges. Although the rising edge
can be used to capture the data, a digital host using the SCK
falling edge allows a faster reading rate and, consequently, more
AD7988-1/ AD7988-5 devices in the chain, provided that the
digital host has an acceptable hold time. The maximum
CHAIN MODE
This mode can be used to daisy-chain multiple AD7988-1/
AD7988-5 devices on a 3-wire serial interface. This feature is
useful for reducing component count and wiring connections, for
example, in isolated multiconverter applications or for systems
with a limited interfacing capacity. Data readback is analogous
to clocking a shift register.
A connection diagram example using the AD7988-1/AD7988-5
devices is shown in Figure 38, and the corresponding timing is
given in Figure 39.
When SDI and CNV are low, SDO is driven low. With SCK low,
a rising edge on CNV initiates a conversion and selects the chain
mode. In this mode, CNV is held high during the conversion
conversion rate may be reduced due to the total readback time.
CONVERT
CNV
CNV
DIGITAL HOST
AD7988-1/
AD7988-5
AD7988-1/
AD7988-5
SDI
SDO
SDI
SDO
DATA IN
A
SCK
B
SCK
CLK
Figure 38. Chain Mode Connection Diagram
SDI = 0
A
tCYC
CNV
tCONV
tACQ
CONVERSION
ACQUISITION
ACQUISITION
tSCK
tSCKL
tSSCKCNV
SCK
1
2
3
A
B
14
15
16
17
18
30
31
32
tSSDISCK
tSCKH
tHSCKCNV
tHSDISCK
tEN
SDO = SDI
A
D
15
D
14
D
D
13
13
D
A
1
D
A
0
B
A
A
tHSDO
tDSDO
D
B
15
D
14
D
1
D
0
D
15
D
14
D 1
A
D 0
A
SDO
B
B
B
A
A
B
Figure 39. Chain Mode Serial Interface Timing
Rev. G | Page 21 of 24
AD7988-1/AD7988-5
Data Sheet
APPLICATIONS INFORMATION
Using at least one ground plane is recommended. It can be
INTERFACING TO BLACKFIN® DSP
common or split between the digital and analog section. In the
latter case, join the planes underneath the AD7988-1/AD7988-5
devices.
The AD7988-1/AD7988-5 voltage reference input, REF, has a
dynamic input impedance. Decouple REF with minimal parasitic
inductances by placing the reference decoupling ceramic capacitor
close to, but ideally right up against, the REF and GND pins and
connecting them with wide, low impedance traces.
The AD7988-1/AD7988-5 can easily connect to a DSP SPI or
SPORT. The SPI configuration is straightforward, using the
standard SPI interface as shown in Figure 40.
SPI_CLK
SPI_MISO
SPI_MOSI
SCK
SDO
CNV
AD7988-1/
AD7988-5
BLACKFIN
DSP
Finally, decouple the power supplies of the AD7988-1/AD7988-5,
VDD and VIO, with ceramic capacitors, typically 100 nF, placed
close to the AD7988-1/AD7988-5 and connected using short and
wide traces to provide low impedance paths and to reduce the
effect of glitches on the power supply lines.
Figure 40. Typical Connection to Blackfin SPI Interface
Similarly, the SPORT interface can be used to interface to this
ADC. The SPORT interface has some benefits in that it can use
direct memory access (DMA) and provides a lower jitter CNV
signal generated from a hardware counter.
An example of a layout following these rules is shown in Figure 42
and Figure 43.
Some glue logic may be required between SPORT and the
AD7988-1/AD7988-5 interface. The evaluation board for the
AD7988-1/AD7988-5 interfaces directly to the SPORT of the
Blackfin-based (ADSP-BF527) SDP board. The configuration
used for the SPORT interface requires the addition of some glue
logic as shown in Figure 41. The SCK input to the ADC was
gated off when CNV was high to keep the SCK line static while
converting the data, thereby ensuring the best integrity of the
result. This approach uses an AND gate and a NOT gate for the
SCK path. The other logic gates used on the RSCLK and RFS
paths are for delay matching purposes and may not be
necessary where path lengths are short.
EVALUATING THE PERFORMANCE OF THE
AD7988-1/AD7988-5
The evaluation board package for the AD7988-1/AD7988-5
(EVAL-AD7988-5SDZ) includes a fully assembled and tested
evaluation board, documentation, and software for controlling the
board from a PC via the EVAL-SDP-CB1Z.
AD7988-1/
AD7988-5
This is one approach to using the SPORT interface for this ADC;
there may be other solutions equal to this approach.
VDRIVE
DR
SDO
SCK
RSCLK
TSCLK
BLACKFIN
DSP
AD7988-1/
AD7988-5
RFS
TFS
Figure 42. Example Layout of the AD7988-1/AD7988-5 (Top Layer)
CNV
Figure 41. Evaluation Board Connection to Blackfin Sport Interface
LAYOUT
Design the printed circuit board (PCB) that houses the AD7988-1/
AD7988-5 so that the analog and digital sections are separated
and confined to certain areas of the board. The pinout of the
AD7988-1/AD7988-5, with all the analog signals on the left side
and all the digital signals on the right side, eases this task.
Avoid running digital lines under the device because these couple
noise onto the die, unless a ground plane under the AD7988-1/
AD7988-5 is used as a shield. Fast switching signals, such as
CNV or clocks, should never run near analog signal paths.
Avoid crossover of digital and analog signals.
Figure 43. Example Layout of the AD7988-1/AD7988-5 (Bottom Layer)
Rev. G | Page 22 of 24
Data Sheet
AD7988-1/AD7988-5
OUTLINE DIMENSIONS
3.10
3.00
2.90
10
1
6
5
5.15
4.90
4.65
3.10
3.00
2.90
PIN 1
IDENTIFIER
0.50 BSC
0.95
0.85
0.75
15° MAX
1.10 MAX
0.70
0.55
0.40
0.15
0.05
0.23
0.13
6°
0°
0.30
0.15
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-187-BA
Figure 44.10-Lead Mini Small Outline Package [MSOP]
(RM-10)
Dimensions shown in millimeters
DETAIL A
(JEDEC 95)
2.48
2.38
2.23
3.10
3.00 SQ
0.50 BSC
2.90
10
6
PIN 1 INDEX
EXPOSED
PAD
1.74
1.64
1.49
AREA
0.50
0.40
0.30
0.20 MIN
PIN 1
INDIC ATOR AREA OPTIONS
(SEE DETAIL A)
1
5
BOTTOM VIEW
TOP VIEW
SIDE VIEW
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
0.80
0.75
0.70
0.05 MAX
0.02 NOM
COPLANARITY
0.08
SECTION OF THIS DATA SHEET.
SEATING
PLANE
0.30
0.25
0.20
0.20 REF
Figure 45. 10-Lead Lead Frame Chip Scale Package [LFCSP]
3 mm × 3 mm Body and 0.75 mm Package Height
(CP-10-9)
Dimensions shown in millimeters
Rev. G | Page 23 of 24
AD7988-1/AD7988-5
Data Sheet
ORDERING GUIDE
Integral
Temperature
Range
Ordering
Quantity
Package
Option
Model1, 2, 3
Nonlinearity
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
1.25 LSB max
Package Description
10-Lead MSOP
10-Lead MSOP
10-Lead LFCSP
10-Lead LFCSP
10-Lead MSOP
10-Lead MSOP
10-Lead LFCSP
10-Lead LFCSP
10-Lead LFCSP
10-Lead LFCSP
Branding
C7E
C7E
C7X
C7X
C7Q
C7Q
C7Z
AD7988-1BRMZ
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Tube, 50
RM-10
RM-10
CP-10-9
CP-10-9
RM-10
AD7988-1BRMZ-RL7
AD7988-1BCPZ-RL
AD7988-1BCPZ-RL7
AD7988-5BRMZ
AD7988-5BRMZ-RL7
AD7988-5BCPZ-RL
AD7988-5BCPZ-RL7
AD7988-5CCPZ-RL
AD7988-5CCPZ-RL7
EVAL-AD7988-5SDZ
Reel, 1,000
Reel, 5,000
Reel, 1,500
Tube, 50
Reel, 1,000
Reel, 5,000
Reel, 1,500
Reel, 5,000
Reel, 1,500
RM-10
CP-10-9
CP-10-9
CP-10-9
CP-10-9
C7Z
C8P
C8P
Evaluation Board with the AD7988-5
Populated; Use for the Evaluation of both
the AD7988-1 and the AD7988-5
EVAL-SDP-CB1Z
System Demonstration Board; Used as a
Controller Board for Data Transfer via USB
Interface to PC
1 Z = RoHS Compliant Part.
2 The EVAL-AD7988-5SDZ can be used as a standalone evaluation board or in conjunction with the EVAL-SDZ-CB1Z for evaluation and/or demonstration purposes.
3 The EVAL-SDP-CB1Z allows a PC to control and communicate with all Analog Devices, Inc., evaluation boards ending in the SD designator.
©2012–2017 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D10231-0-10/17(G)
Rev. G | Page 24 of 24
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