16-Bit, 10 MSPS, PulSAR

Differential ADC
AD7626
FEATURES FUNCTIONAL BLOCK DIAGRAM
REFIN REF VCM
Throughput: 10 MSPS
SNR: 91.5 dB
1.2V ÷2 CLOCK VIO
16-bit no missing codes BAND GAP
LOGIC
INL: ±0.45 LSB IN+ CAP CNV+, CNV–
DNL: ±0.35 LSB IN– DAC

Power dissipation: 136mW D+, D–

SERIAL
32-lead LFCSP (5 mm × 5 mm) SAR
LVDS DCO+, DCO–

07648-001
AD7626
SAR architecture CLK+, CLK–

No latency/no pipeline delay

Figure 1.
16-bit resolution with no missing codes
Zero error: ±1LSB GENERAL DESCRIPTION
Differential input range: ±4.096 V The AD7626 is a 16-bit, 10 MSPS, charge redistribution
Serial LVDS interface successive approximation register (SAR) based architecture
Self-clocked mode analog-to-digital converter (ADC). SAR architecture allows
Echoed-clock mode unmatched performance both in noise (91.5 dB SNR) and in
LVDS or CMOS option for conversion control (CNV signal) linearity (±0.45 LSB INL). The AD7626 contains a high speed,
Reference options 16-bit sampling ADC, an internal conversion clock, and an
Internal: 4.096 V internal buffered reference. On the CNV edge, it samples the
External (1.2 V) buffered to 4.096 V voltage difference between the IN+ and IN− pins. The voltages
External: 4.096 V on these pins swing in opposite phase between 0 V and REF.
APPLICATIONS The 4.096 V reference voltage, REF, can be generated internally
or applied externally.
Digital imaging systems
Digital X-ray All converted results are available on a single LVDS self-clocked
Digital MRI or echoed-clock serial interface, reducing external hardware
CCD and IR cameras connections.
High speed data acquisition The AD7626 is housed in a 32-lead, 5 mm × 5 mm LFCSP with
High dynamic range telecommunications receivers operation specified from −40°C to +85°C.
Spectrum analysis
Test equipment

Table 1. Fast PulSAR® ADC Selection

Input Type Resolution (Bits) 1 MSPS to <2 MSPS 2 MSPS to 3 MSPS 6 MSPS 10 MSPS
Differential (Ground Sense) 16 AD7653
AD7667
AD7980
AD7983
True Bipolar 16 AD7671
Differential (Antiphase) 16 AD7677 AD7621 AD7625 AD7626
AD7623 AD7622
Differential (Antiphase) 18 AD7643 AD7641
AD7982
AD7984

Rev. A
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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Tel: 781.329.4700 www.analog.com
Trademarks and registered trademarks are the property of their respective owners. Fax: 781.461.3113 ©2009–2010 Analog Devices, Inc. All rights reserved.
AD7626

TABLE OF CONTENTS
Features .............................................................................................. 1 Theory of Operation ...................................................................... 15
Applications ....................................................................................... 1 Circuit Information.................................................................... 15
Functional Block Diagram .............................................................. 1 Converter Information .............................................................. 15
General Description ......................................................................... 1 Transfer Functions ..................................................................... 16
Revision History ............................................................................... 2 Analog Inputs ............................................................................. 16
Specifications..................................................................................... 3 Typical Connection Diagram ................................................... 17
Timing Specifications .................................................................. 5 Driving the AD7626................................................................... 18
Timing Diagrams.......................................................................... 6 Voltage Reference Options ........................................................ 20
Absolute Maximum Ratings............................................................ 7 Power Supply............................................................................... 21
Thermal Resistance ...................................................................... 7 Digital Interface .......................................................................... 22
ESD Caution .................................................................................. 7 Applications Information .............................................................. 24
Pin Configuration and Function Descriptions ............................. 8 Layout, Decoupling, and Grounding ....................................... 24
Typical Performance Characteristics ........................................... 10 Outline Dimensions ....................................................................... 25
Terminology .................................................................................... 14 Ordering Guide .......................................................................... 25

REVISION HISTORY
1/10—Rev. 0 to Rev. A
Changes to Description of Pin 5 and Pin 6, Table 6..................... 8
Changes to Power-Up Section ...................................................... 21

9/09—Revision 0: Initial Version

Rev. A | Page 2 of 2
 AD7626

SPECIFICATIONS
VDD1 = 5 V; VDD2 = 2.5 V; VIO = 2.5 V; REF = 4.096 V; all specifications TMIN to TMAX, unless otherwise noted.
Table 2.
Parameter Test Conditions/Comments Min Typ Max Unit
RESOLUTION 16 Bits
ANALOG INPUT
Voltage Range VIN+ − VIN− −VREF +VREF V
Operating Input Voltage VIN+, VIN− to AGND −0.1 VREF + 0.1 V
Common-Mode Input Range VREF/2 − 0.05 VREF/2 VREF/2 + 0.05 V
CMRR fIN = 1 MHz 68 dB
Input Current Midscale input 168 μA
THROUGHPUT
Complete Cycle 100 ns
Throughput Rate 0.1 10 MSPS
DC ACCURACY
Integral Linearity Error −1.5 ±0.45 +1.5 LSB
No Missing Codes 16 Bits
Differential Linearity Error −0.5 ±0.35 +0.5 LSB
Transition Noise 0.6 LSB
Zero Error, TMIN to TMAX −6 ±1 +6 LSB
Zero Error Drift 0.5 ppm/°C
Gain Error, TMIN to TMAX 8 20 LSB
Gain Error Drift 0.7 ppm/°C
Power Supply Sensitivity 1 VDD1 = 5 V ± 5% 0.4 LSB
VDD2 = 2.5 V ± 5% 0.2 LSB
AC ACCURACY
fIN = 20 kHz, −0.5 dBFS
Dynamic Range 90.5 91.5 dB
Signal-to-Noise Ratio 90 91 dB
Spurious-Free Dynamic Range 105 dB
Total Harmonic Distortion −105.5 dB
Signal-to-(Noise + Distortion) 89.5 91 dB
fIN = 100 kHz, −0.5 dBFS
Signal-to-Noise Ratio 91.3 dB
Spurious-Free Dynamic Range 104.5 dB
Total Harmonic Distortion −102.5 dB
Signal-to-(Noise + Distortion) 91 dB
fIN = 2.4 MHz, −1 dBFS
Signal-to-Noise Ratio 88.5 dBFS
Spurious-Free Dynamic Range 84 dB
Total Harmonic Distortion −86 dB
Signal-to-(Noise + Distortion) 85 dB
fIN = 2.4 MHz, −6 dBFS
Signal-to-Noise Ratio 89 dBFS
Spurious-Free Dynamic Range 84 dB
Total Harmonic Distortion −93 dB
Signal-to-(Noise + Distortion) 88 dB
−3 dB Input Bandwidth 95 MHz
Aperture Jitter 0.25 ps rms
INTERNAL REFERENCE
Output Voltage REFIN @ 25°C 1.18 1.19 1.2 V
Temperature Drift −40°C to +85°C ±15 ppm/°C

Rev. A | Page 3 of 
AD7626
Parameter Test Conditions/Comments Min Typ Max Unit
REFERENCE BUFFER
REFIN Input Voltage Range 1.18 1.2 1.22 V
REF Output Voltage Range REF @ 25°C, EN0 = EN1 = 1 4.076 4.096 4.116 V
Line Regulation VDD1 ± 5%, VDD2 ± 5% 5 mV
EXTERNAL REFERENCE
Voltage Range REF 4.096 V
VCM PIN
VCM Output REF/2
VCM Error −0.015 +0.015 V
Output Impedance 5 kΩ
LVDS I/O (ANSI-644)
Data Format Serial LVDS twos complement
Differential Output Voltage, VOD RL = 100 Ω 245 290 454 mV
Common-Mode Output Voltage, VOCM RL = 100 Ω 980 2 1130 1375 mV
Differential Input Voltage, VID 100 650 mV
Common-Mode Input Voltage, VICM 800 1575 mV
POWER SUPPLIES
Specified Performance
VDD1 4.75 5 5.25 V
VDD2 2.37 2.5 2.63 V
VIO 2.37 2.5 2.63 V
Operating Currents
Static—Not Converting
VDD1 3.5 4.5 mA
VDD2 16.7 21.2 mA
VIO 11.6 13.5 mA
With Internal Reference 10 MSPS throughput
VDD1 10.4 11.2 mA
VDD2 23.5 27.8 mA
VIO Echoed-clock mode 15.8 17.8 mA
With External Reference 10 MSPS throughput
VDD1 7.5 8.8 mA
VDD2 23 28 mA
VIO Echoed-clock mode 16.4 18.5 mA
Power-Down EN0 = 0, EN1 = 0
VDD1 0.6 4 μA
VDD2 0.8 10 μA
VIO 1 5 μA
Power Dissipation 3
Static—Not Converting 88 107 mW
With Internal Reference 10 MSPS throughput 150 170 mW
With External Reference 10 MSPS throughput 136 160 mW
Power-Down 8 58 μW
Energy per Conversion 10 MSPS throughput 13.6 nJ/sample
TEMPERATURE RANGE
Specified Performance TMIN to TMAX −40 +85 °C
1
Using an external reference.
2
The ANSI-644 LVDS specification has a minimum output common mode (VOCM) of 1125 mV.
3
Power dissipation is for the AD7626 device only. In self-clocked interface mode, 0.9 mW is dissipated in the 100 Ω terminator. In echoed-clock interface mode, 1.8 mW
is dissipated in two 100 Ω terminators.

Rev. A | Page 4 of 
 AD7626
TIMING SPECIFICATIONS
VDD1 = 5 V; VDD2 = 2.5 V; VIO = 2.37 V to 2.63 V; REF = 4.096 V; all specifications TMIN to TMAX, unless otherwise noted.

Table 3.
Parameter Symbol Min Typ Max Unit
Time Between Conversions 1 tCYC 100 10,000 ns
CNV High Time tCNVH 10 40 ns
CNV to D (MSB) Ready tMSB 100 ns
CNV to Last CLK (LSB) Delay tCLKL 72 ns
CLK Period 2 tCLK 3.33 4 (tCYC − tMSB + tCLKL)/n ns
CLK Frequency fCLK 250 300 MHz
CLK to DCO Delay (Echoed-Clock Mode) tDCO 0 4 7 ns
DCO to D Delay (Echoed-Clock Mode) tD 0 1 ns
CLK to D Delay tCLKD 0 4 7 ns
1
The maximum time between conversions is 10,000 ns. If CNV± is left idle for a time greater than the maximum value of tCYC, the subsequent conversion result is invalid.
2
For the maximum CLK period, the window available to read data is tCYC − tMSB + tCLKL. Divide this time by the number of bits (n) to be read giving the maximum CLK±
frequency that can be used for a given conversion CNV frequency. In echoed-clock interface mode, n = 16; in self-clocked interface mode, n = 18.

Rev. A | Page 5 of 
AD7626
TIMING DIAGRAMS
SAMPLE N SAMPLE N + 1
tCYC

tCNVH

CNV–

CNV+

ACQUISITION ACQUISITION ACQUISITION

tCLKL
tCLK
15 16 1 2 15 16 1 2 3
CLK–

CLK+
tDCO
15 16 1 2 15 16 1 2 3
DCO–

DCO+
tMSB tD
tCLKD
D+

07648-003
D1 D0 D15 D14 D1 D0 0 D15 D14 D13
N–1 N–1 0 N N N N N+1 N+1 N+1
D–

Figure 2. Echoed-Clock Interface Mode Timing Diagram

SAMPLE N SAMPLE N + 1
tCYC

tCNVH

CNV–

CNV+

ACQUISITION ACQUISITION ACQUISITION

tCLK tCLKL

17 18 1 2 3 4 17 18 1 2 3
CLK–

CLK+
tMSB
tCLKD
D+
07648-004

D1 D0 D15 D14 D1 D0 D15

0 1 0 0 1 0 N+1
N–1 N–1 N N N N
D–

Figure 3. Self-Clocked Interface Mode Timing Diagram

Rev. A | Page 6 of 
 AD7626

ABSOLUTE MAXIMUM RATINGS

Table 4. THERMAL RESISTANCE
Parameter Rating θJA is specified for the worst-case conditions, that is, a device
Analog Inputs/Outputs soldered in a circuit board for surface-mount packages.
IN+, IN− to GND1 −0.3 V to REF + 0.3 V or
±130 mA Table 5. Thermal Resistance
2
REF to GND −0.3 V to +6 V Package Type θJA θJC Unit
VCM, CAP2 to GND −0.3 V to +6 V 32-Lead LFCSP_VQ 40 4 °C/W
CAP1, REFIN to GND −0.3 V to +2.7 V
Supply Voltage
VDD1 −0.3 V to +6 V ESD CAUTION
VDD2, VIO −0.3 V to +3 V
Digital Inputs to GND −0.3 V to VIO + 0.3 V
Digital Outputs to GND −0.3 V to VIO + 0.3 V
Input Current to Any Pin Except ±10 mA
Supplies3
Operating Temperature Range −40°C to +85°C
(Commercial)
Storage Temperature Range −65°C to +150°C
Junction Temperature 150°C
ESD 1 kV
1
See the Analog Inputs section.
2
Keep CNV± low for any external REF voltage > 4.3 V applied to the REF pin.
3
Transient currents of up to 100 mA do not cause SCR latch-up.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

Rev. A | Page 7 of 
AD7626

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

CAP2

CAP2
CAP2
GND

GND
REF

REF
REF
29
28
27
26
25
31
30
32
VDD1 1 24 GND
VDD2 2 PIN 1 23 IN+
INDICATOR
CAP1 3 22 IN–
REFIN 4 AD7626 21 VCM
EN0 5 20 VDD1
TOP VIEW VDD1
EN1 6 (Not to Scale) 19
VDD2 7 18 VDD2
CNV– 8 17 CLK+

11
9

13
14
15
10

12

16
VIO
GND
D+

DCO+
D–

DCO–

CLK–
CNV+

07648-002
NOTES
1. CONNECT THE EXPOSED PAD TO THE GROUND
PLANE OF THE PCB USING MULTIPLE VIAS.

Figure 4. Pin Configuration

Table 6. Pin Function Descriptions

Pin No. Mnemonic Type1 Description
1 VDD1 P Analog 5 V Supply. Decouple the 5 V supply with a 100 nF capacitor.
2 VDD2 P Analog 2.5 V Supply. Decouple this pin with a 100 nF capacitor. The 2.5 V supply source should
supply this pin first, then be traced to the other VDD2 pins (Pin 7 and Pin 18).
3 CAP1 AO Connect this pin to a 10 nF capacitor.
4 REFIN AI/O Prebuffer Reference Voltage. When using the internal reference, this pin outputs the band gap voltage
and is nominally at 1.2 V. It can be overdriven with an external reference voltage such as the ADR280.
In either internal or external reference mode, a 10 μF capacitor is required. If using an external 4.096 V
reference (connected to REF), this pin is a no connect and does not require any capacitor.
5, 6 EN0, EN1 DI Enable. Operates from 2.5 V logic. The logic levels of these pins set the operation of the device as
follows:
EN1 = 0, EN0 = 0: power-down mode.
EN1 = 0, EN0 = 1: external 1.2 V reference applied to the REFIN pin required.
EN1 = 1, EN0 = 0: external 4.096 V reference applied to the REF pin required.
EN1 = 1, EN0 = 1: internal reference and internal reference buffer in use.
7 VDD2 P Digital 2.5 V Supply. Decouple this pin with a 100 nF capacitor.
8, 9 CNV−, CNV+ DI Convert Input. These pins act as the conversion control pin. On the rising edge of these pins, the
analog inputs are sampled and a conversion cycle is initiated. CNV+ works as a CMOS input when
CNV− is grounded; otherwise, CNV+ and CNV− are differential LVDS inputs.
10, 11 D−, D+ DO LVDS Data Outputs. The conversion data is output serially on these pins.
12 VIO P Input/Output Interface Supply. Use a 2.5 V supply and decouple this pin with a 100 nF capacitor.
13 GND P Ground. Return path for the 100 nF capacitor connected to Pin 12.
14, 15 DCO−, DCO+ DO LVDS Buffered Clock Outputs. When DCO+ is grounded, the self-clocked interface mode is selected.
In this mode, the 16-bit results on D are preceded by an initial 0 (which is output at the end of the
previous conversion), followed by a 2-bit header (10) to allow synchronization of the data by the
digital host with extra logic. The 1 in this header provides the reference to acquire the subsequent
conversion result correctly. When DCO+ is not grounded, the echoed-clock interface mode is
selected. In this mode, DCO± is a copy of CLK±. The data bits are output on the falling edge of DCO+
and can be captured in the digital host on the next rising edge of DCO+.
16, 17 CLK−, CLK+ DI LVDS Clock Inputs. This clock shifts out the conversion results on the falling edge of CLK+.
18 VDD2 P Analog 2.5 V Supply. Decouple this pin with a 100 nF capacitor.
19, 20 VDD1 P Analog 5 V Supply. Isolate these pins from Pin 1 with a ferrite bead and decouple them with a 100 nF
capacitor.
21 VCM AO Common-Mode Output. When using any reference scheme, this pin produces one-half the voltage
present on the REF pin, which can be useful for driving the common mode of the input amplifiers.
22 IN− AI Differential Negative Analog Input. Referenced to and must be driven 180° out of phase with IN+.

Rev. A | Page 8 of 28
 AD7626
Pin No. Mnemonic Type 1 Description
23 IN+ AI Differential Positive Analog Input. Referenced to and must be driven 180° out of phase with IN−.
24 GND P Ground.
25, 26, 28 CAP2 AO Connect all three CAP2 pins together and decouple them with the shortest trace possible to a single
10 μF, low ESR, low ESL capacitor. The other side of the capacitor must be placed close to Pin 27 (GND).
27 GND P Ground. Return path for the 10 μF capacitor connected to Pin 25, Pin 26, and Pin 28.
29, 30, 32 REF AI/O Buffered Reference Voltage. When using the internal reference or the 1.2 V external reference (REFIN
input), the 4.096 V system reference is produced at this pin. When using an external reference, such
as the ADR434 or the ADR444, the internal reference buffer must be disabled. In either case, connect
all three REF pins together and decouple them with the shortest trace possible to a single 10 μF, low
ESR, low ESL capacitor. The other side of the capacitor must be placed close to Pin 31 (GND).
31 GND P Ground. Return path for the 10 μF capacitor connected to Pin 29, Pin 30, and Pin 32.
EP Exposed pad The exposed pad is located on the underside of the package. Connect the exposed pad to the
ground plane of the PCB using multiple vias. See the Exposed Paddle section for more information.
1
AI = analog input; AI/O = bidirectional analog; AO = analog output; DI = digital input; DO = digital output; P = power.

Rev. A | Page 9 of 
AD7626

TYPICAL PERFORMANCE CHARACTERISTICS

VDD1 = 5 V; VDD2 = 2.5 V; VIO = 2.5 V; REF = 4.096 V; all plots at 10 MSPS unless otherwise noted. FFT plots for 2 MHz, 3 MHz, and
5 MHz input tones use band pass filter (±400 kHz pass bandwidth around fundamental frequency).
0 0
INPUT FREQUENCY = 10.37kHz INPUT FREQUENCY = 100kHz
SNR = 91.85dB SNR = 91.323dB
–20 SINAD = 91.8dB –20 SINAD = 91.047dB
THD = –112.1dB THD = –102.543dB
–40 SFDR = 112.85dB –40 SFDR = 104.529dB
32k SAMPLES

–60 –60
AMPLITUDE (dB)

AMPLITUDE (dB)
–80 –80

–100 –100

–120 –120

–140 –140

–160 –160

–180 –180
07648-108

07648-118
0 10 30 50 70 90 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
FREQUENCY (kHz) FREQUENCY (MHz)

Figure 5. 10 kHz, −0.5 dB Input Tone, Zoomed View Figure 8.100 kHz, −0.5 dB Input Tone FFT, Full Frequency View

0 0
INPUT FREQUENCY = 2.0026MHz INPUT FREQUENCY = 2.0026MHz
–0.5dB INPUT AMPLITUDE –6dB INPUT AMPLITUDE
–20 SNR = 87.4dBFS –20 SNR = 87.6dBFS
SINAD = 84.8dBFS SINAD = 87.6dBFS
THD = –87.9dB THD = –101.6dB
–40 SFDR = 88.1dB –40 SFDR = 101.9dB
64k SAMPLES 64k SAMPLES

–60 –60
AMPLITUDE (dB)

AMPLITUDE (dB)

THIRD
HARMONIC
–80 FIFTH –80
SECOND FIFTH THIRD
HARMONIC HARMONIC HARMONIC HARMONIC
–100 SECOND
–100 HARMONIC

–120 –120

–140 –140

–160 –160

–180 –180
07648-402

07648-409
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
FREQUENCY (MHz) FREQUENCY (MHz)
Figure 6. FFT, 2 MHz, −0.5 dB Input Tone, Wide View Figure 9. FFT, 2 MHz, −6 dB Input Tone, Wide View

0 0
INPUT FREQUENCY = 3.00125MHz INPUT FREQUENCY = 3.00125MHz
–0.5dB INPUT AMPLITUDE –6dB INPUT AMPLITUDE
–20 SNR = 87.1dBFS –20 SNR = 88.48dBFS
SINAD = 81.2dBFS SINAD = 88.3dBFS
THD = –82.0dB THD = –97.2dB
–40 SFDR = 82.1dB –40 SFDR = 98.3dB
64k SAMPLES 64k SAMPLES

–60 –60
AMPLITUDE (dB)
AMPLITUDE (dB)

THIRD
HARMONIC
–80 FIFTH –80
SECOND HARMONIC THIRD SECOND
HARMONIC HARMONIC HARMONIC FIFTH
FOURTH
–100 HARMONIC –100 HARMONIC
FOURTH
HARMONIC
–120 –120

–140 –140

–160 –160

–180 –180
07648-411
07648-404

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
FREQUENCY (MHz) FREQUENCY (MHz)

Figure 7. FFT, 3 MHz, −0.5 dB Input Tone, Wide View Figure 10. FFT, 3 MHz, −6 dB Input Tone, Wide View

Rev. A | Page 10 of 
 AD7626
0 0
INPUT FREQUENCY = 5.00656128MHz INPUT FREQUENCY = 5.00656128MHz
–0.5dB INPUT AMPLITUDE –0.5dB INPUT AMPLITUDE
–20 SNR = 86.7dBFS –20 SNR = 86.7dBFS
SINAD = 83.2dBFS SINAD = 83.2dBFS FUNDAMENTAL
THD = –85.3dB THD = –85.3dB
–40 SFDR = 86.1dB –40 SFDR = 86.1dB
64k SAMPLES 64k SAMPLES

–60 –60
AMPLITUDE (dB)

AMPLITUDE (dB)
THIRD THIRD
HARMONIC HARMONIC
–80 –80
SECOND FIFTH FIFTH
HARMONIC HARMONIC HARMONIC
–100 –100
FOURTH
HARMONIC
–120 –120

–140 –140

–160 –160

–180 –180

07648-406

07648-412
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 4.50 4.55 4.60 4.65 4.70 4.75 4.80 4.85 4.90 4.95 5.00
FREQUENCY (MHz) FREQUENCY (MHz)

Figure 11. FFT, 5 MHz, −0.5 dB Input Tone, Wide View Figure 14. FFT, 5 MHz, −0.5 dB Input Tone Zoomed View

0 0
INPUT FREQUENCY = 5.00656128MHz INPUT FREQUENCY = 5.00656128MHz
–6dB INPUT AMPLITUDE –6dB INPUT AMPLITUDE
–20 SNR = 88.4dBFS –20 SNR = 88.4dBFS
SINAD = 88.0dBFS FUNDAMENTAL SINAD = 88.0dBFS FUNDAMENTAL
THD = –92.4dB THD = –92.4dB
–40 SFDR = 92.8dB –40 SFDR = 92.8dB
64k SAMPLES 64k SAMPLES

–60 –60
AMPLITUDE (dB)

–80 THIRD AMPLITUDE (dB) –80 THIRD

SECOND HARMONIC HARMONIC
HARMONIC FIFTH HARMONIC
–100 –100
FOURTH FIFTH
HARMONIC HARMONIC
–120 –120

–140 –140

–160 –160

–180 –180
07648-413

07648-407
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 4.50 4.55 4.60 4.65 4.70 4.75 4.80 4.85 4.90 4.95 5.00
FREQUENCY (MHz) FREQUENCY (MHz)

Figure 12. FFT, 5 MHz, −6 dB Input Tone, Wide View Figure 15. FFT, 5 MHz, −0.5 dB Input Tone Zoomed View

–75 94 –50

–80 92
9.7MHz –60
–85
90
5MHz –70
–90
SNR (dBFS)

SNR
THD (dB)

THD (dB)
88
–95 –80
1MHz 86
–100
–90
84
–105

3MHz –100
–110 82
2MHz THD
07648-401

–115 80 –110
07648-211

–18 –15 –12 –9 –6 –3 0 10k 100k 1M 10M

INPUT AMPLITUDE (dBFS) INPUT FREQUENCY (Hz)

Figure 13. THD vs. Input Amplitudes at Input Frequency Tones of Figure 16. THD and SNR vs. Input Frequency (−0.5 dB Input Tone)
10 kHz to 9.7 MHz

Rev. A | Page 11 of 
AD7626
92.0 92.0

91.8 91.8

91.6 91.6

91.4 91.4

91.2 91.2

SINAD (dB)
SNR (dB)

EXTERNAL REFERENCE
91.0 91.0 EXTERNAL REFERENCE

90.8 90.8
INTERNAL REFERENCE
90.6 90.6 INTERNAL REFERENCE

90.4 90.4

90.2 90.2

90.0 90.0

07648-212

07648-215
–40 –20 0 20 40 60 80 –40 –20 0 20 40 60 80
TEMPERATURE (°C) TEMPERATURE (°C)

Figure 17. SNR vs. Temperature (−0.5 dB, 20 kHz Input Tone) Figure 20. SINAD vs. Temperature (−0.5 dB, 20 kHz Input Tone)

0.35 7

0.30

ZERO ERROR AND GAIN ERROR (LSB)

6

0.25
5 GAIN ERROR
+INPUT CURRENT
INPUT URRENT (mA)

0.20
4
0.15
3
0.10
2
0.05
–INPUT CURRENT
0 1

–0.05 0 ZERO ERROR

–0.10 –1
07648-121

07648-301
–6 –4 –2 0 2 4 6 –40 –20 0 20 40 60 80
INPUT COMMON-MODE VOLTAGE (V) TEMPERATURE (°C)
Figure 18. Input Current (IN+, IN−) vs. Differential Input Voltage (10 MSPS) Figure 21. Zero Error and Gain Error vs. Temperature

–103.0 250,000
262,144 SAMPLES
STD DEVIATION = 0.4829
–103.5
201,320
200,000
–104.0 EXTERNAL REFERENCE

–104.5
150,000
THD (dB)

COUNT

–105.0

–105.5 100,000

–106.0
50,000
INTERNAL REFERENCE
30,651 30,073
–106.5

0 54 46 0
–107.0 0
07648-214

07648-022

–40 –20 0 20 40 60 80 FEC7 FEC8 FEC9 FECA FECB FECC FECD

TEMPERATURE (°C) CODE (HEX)
Figure 19. THD vs. Temperature (−0.5 dB, 20 kHz Input Tone) Figure 22. Histogram of 262,144 Conversions of a DC Input
at the Code Center (Internal Reference)

Rev. A | Page 12 of 2
 AD7626

250,000 0.30
262,144 SAMPLES
STD DEVIATION = 0.4814 0.25
201,614 0.20
200,000
0.15

0.10
150,000

DNL (LSB)
0.05
COUNT

100,000 –0.05

–0.10
–0.15
50,000
30,206 30,250 –0.20
–0.25
0 41 33 0
0 –0.30

07648-112
07648-024
FEC8 FEC9 FECA FECB FECC FECD FECE 0 16,384 32,768 49,152 65,536
CODE (HEX) CODE

Figure 23. Histogram of 262,144 Conversions of a DC Input Figure 25. Differential Nonlinearity vs. Code (25ºC)
at the Code Center (External Reference)

140,000 0.8
128,084 129,601 262,144 SAMPLES +85°C
STD DEVIATION = 0.5329 +25°C
120,000 0.6 –40°C

0.4
100,000

0.2
INL (LSB)

80,000
COUNT

0
60,000
–0.2
40,000
–0.4

20,000
–0.6
2130 2329
0 0
0 –0.8
07648-023

07648-115
FEC6 FEC7 FEC8 FEC9 FECA FECB 0 16,384 32,768 49,152 65,536
CODE (HEX) CODE

Figure 24. Histogram of 262,144 Conversions of a DC Input Figure 26. Integral Nonlinearity vs. Code vs. Temperature
at the Code Transition

Rev. A | Page 13 of 
AD7626

TERMINOLOGY
Common-Mode Rejection Ratio (CMRR) Power Supply Rejection Ratio (PSRR)
CMRR is defined as the ratio of the power in the ADC output Variations in power supply affect the full-scale transition but not
at full-scale frequency, f, to the power of a 100 mV p-p sine the linearity of the converter. PSRR is the maximum change in
wave applied to the common-mode voltage of VIN+ and VIN− the full-scale transition point due to a change in power supply
at frequency, fS. voltage from the nominal value.

CMRR (dB) = 10 log(Pf/PfS) Reference Voltage Temperature Coefficient

The reference voltage temperature coefficient is derived from the
where: typical shift of output voltage at 25°C on a sample of parts at the
Pf is the power at frequency, f, in the ADC output. maximum and minimum reference output voltage (VREF) meas-
PfS is the power at frequency, fS, in the ADC output. ured at TMIN, T(25°C), and TMAX. It is expressed in ppm/°C as
Differential Nonlinearity (DNL) Error VREF ( Max ) – VREF ( Min )
In an ideal ADC, code transitions are 1 LSB apart. Differential TCVREF ( ppm/°C ) = ×10 6
VREF ( 25°C ) × ( TMAX – TMIN )
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing where:
codes are guaranteed. VREF (Max) = maximum VREF at TMIN, T(25°C), or TMAX.
Integral Nonlinearity (INL) Error VREF (Min) = minimum VREF at TMIN, T(25°C), or TMAX.
Linearity error refers to the deviation of each individual code VREF (25°C) = VREF at 25°C.
from a line drawn from negative full scale through positive full TMAX = +85°C.
scale. The point used as negative full scale occurs ½ LSB before TMIN = −40°C.
the first code transition. Positive full scale is defined as a level Signal-to-Noise Ratio (SNR)
1½ LSB beyond the last code transition. The deviation is meas- SNR is the ratio of the rms value of the actual input signal to
ured from the middle of each code to the true straight line. the rms sum of all other spectral components below the Nyquist
Dynamic Range frequency, excluding harmonics and dc. The value for SNR is
Dynamic range is the ratio of the rms value of the full scale to expressed in decibels.
the rms noise measured for an input typically at −60 dB. The Signal-to-(Noise + Distortion) Ratio (SINAD)
value for dynamic range is expressed in decibels. SINAD is the ratio of the rms value of the actual input signal to
Effective Number of Bits (ENOB) the rms sum of all other spectral components below the Nyquist
ENOB is a measurement of the resolution with a sine wave frequency, including harmonics but excluding dc. The value for
input. It is related to SINAD and is expressed in bits by SINAD is expressed in decibels.

ENOB = [(SINADdB − 1.76)/6.02] Spurious-Free Dynamic Range (SFDR)

SFDR is the difference, in decibels, between the rms amplitude
Gain Error
of the input signal and the peak spurious signal (including
The first transition (from 100 … 000 to 100 …001) should occur
harmonics).
at a level ½ LSB above nominal negative full scale (−4.0959375 V
for the ±4.096 V range). The last transition (from 011 … 110 to Total Harmonic Distortion (THD)
011 … 111) should occur for an analog voltage 1½ LSB below THD is the ratio of the rms sum of the first five harmonic
the nominal full scale (+4.0959375 V for the ±4.096 V range). components to the rms value of a full-scale input signal and
The gain error is the deviation of the difference between the is expressed in decibels.
actual level of the last transition and the actual level of the first Zero Error
transition from the difference between the ideal levels. Zero error is the difference between the ideal midscale input
Gain Error Drift voltage (0 V) and the actual voltage producing the midscale
output code.
The ratio of the gain error change due to a temperature change
of 1°C and the full-scale range (2N). It is expressed in parts per Zero Error Drift
million. The ratio of the zero error change due to a temperature change
Least Significant Bit (LSB) of 1°C and the full scale code range (2N). It is expressed in parts
The least significant bit, or LSB, is the smallest increment that per million.
can be represented by a converter. For a fully differential input
ADC with N bits of resolution, the LSB expressed in volts is
V INp-p
LSB (V) =
2N

Rev. A | Page 14 of 
 AD7626

THEORY OF OPERATION
IN+
GND

SWITCHES
CONTROL
MSB LSB SW+
32,768C 16,384C 4C 2C C C
REF CLK+, CLK–
(4.096V)
CONTROL DCO+, DCO– DATA TRANSFER
COMP LOGIC
GND D+, D–
OUTPUT CODE
32,768C 16,384C 4C 2C C C
SW–
MSB LSB
CNV+, CNV– LVDS INTERFACE
GND

07648-030
CONVERSION
CONTROL
IN–

Figure 27. ADC Simplified Schematic

CIRCUIT INFORMATION
The AD7626 is a 10 MSPS, high precision, power effi- When the conversion phase begins, SW+ and SW− are opened
cient, 16-bit ADC that uses SAR-based architecture to first. The two capacitor arrays are then disconnected from the
provide a performance of 91.5 dB SNR, ±0.45 LSB INL, inputs and connected to the GND input. Therefore, the differential
and ±0.35 LSB DNL. voltage between the inputs (IN+ and IN−) captured at the end
The AD7626 is capable of converting 10,000,000 samples per of the acquisition phase is applied to the comparator inputs,
second (10 MSPS). The device typically consumes 136 mW of causing the comparator to become unbalanced. By switching
power. The AD7626 offers the added functionality of a high each element of the capacitor array between GND and 4.096 V
performance on-chip reference and on-chip reference buffer. (the reference voltage), the comparator input varies by binary
weighted voltage steps (VREF/2, VREF/4 … VREF/65,536). The
The AD7626 is specified for use with 5 V and 2.5 V supplies control logic toggles these switches, MSB first, to bring the
(VDD1, VDD2). The interface from the digital host to the comparator back into a balanced condition. At the completion
AD7626 uses 2.5 V logic only. The AD7626 uses an LVDS of this process, the control logic generates the ADC output code.
interface to transfer data conversions. The CNV+ and CNV−
inputs to the part activate the conversion of the analog input. The AD7626 digital interface uses low voltage differential
The CNV+ and CNV− pins can be applied using a CMOS or signaling (LVDS) to enable high data transfer rates.
LVDS source. The AD7626 conversion result is available for reading after
The AD7626 is housed in a space-saving, 32-lead, 5 mm × tMSB (time from the conversion start until MSB is available) has
5 mm LFCSP. elapsed. The user must apply a burst LVDS CLK± signal to the
AD7626 to transfer data to the digital host.
CONVERTER INFORMATION
The CLK± signal outputs the ADC conversion result onto the
The AD7626 is a 10 MSPS ADC that uses SAR-based archi- data output D±. The bursting of the CLK± signal is illustrated
tecture to incorporate a charge redistribution DAC. Figure 27 in Figure 41 and Figure 42 and is characterized as follows:
shows a simplified schematic of the ADC. The capacitive DAC
consists of two identical arrays of 16 binary weighted capacitors • The differential voltage on CLK± should be held steady
that are connected to the two comparator inputs. state in the time between tCLKL and tMSB.
• The AD7626 has two data read modes. For more
During the acquisition phase, the terminals of the array tied
information about the echoed-clock and self-clocked
to the input of the comparator are connected to GND via SW+
interface modes, see the Digital Interface section.
and SW−. All independent switches are connected to the analog
inputs. In this way, the capacitor arrays are used as sampling
capacitors and acquire the analog signal on the IN+ and IN−
inputs. A conversion phase is initiated when the acquisition
phase is complete and the CNV input goes high. Note that the
AD7626 can receive a CMOS or LVDS format CNV signal.

Rev. A | Page 15 of 
AD7626
TRANSFER FUNCTIONS ANALOG INPUTS
The AD7626 uses a 4.096 V reference. The AD7626 converts The analog inputs, IN+ and IN−, applied to the AD7626 must be
the differential voltage of the antiphase analog inputs (IN+ 180° out of phase with each other. Figure 29 shows an equivalent
and IN−) into a digital output. The analog inputs, IN+ and IN−, circuit of the input structure of the AD7626.
require a 2.048 V common-mode voltage (REF/2). The two diodes provide ESD protection for the analog inputs,
The 16-bit conversion result is in MSB first, twos complement IN+ and IN−. Care must be taken to ensure that the analog input
format. signal does not exceed the reference voltage by more than 0.3 V.
The ideal transfer functions for the AD7626 are shown If the analog input signal exceeds this level, the diodes become
in Figure 28 and Table 7. forward-biased and start conducting current. These diodes can
handle a forward-biased current of 130 mA maximum. However,
if the supplies of the input buffer (for example, the supplies of
ADC CODE (TWOS COMPLEMENT)

the ADA4899-1 in Figure 33) are different from those of the

011 ... 111 reference, the analog input signal may eventually exceed the
011 ... 110
011 ... 101 supply rails by more than 0.3 V. In such a case (for example, an
input buffer with a short circuit), the current limitation can be
used to protect the part.
VDD1 CNV

25pF
IN+ 67Ω
100 ... 010 OR IN–
100 ... 001

07648-010
100 ... 000
–FSR –FSR + 1LSB +FSR – 1LSB
07648-031

–FSR + 0.5LSB +FSR – 1.5LSB Figure 29. Equivalent Analog Input Circuit
ANALOG INPUT
The analog input structure allows the sampling of the true
Figure 28. ADC Ideal Transfer Functions (FSR = Full-Scale Range)
differential signal between IN+ and IN−. By using these differ-
Table 7. Output Codes and Ideal Input Voltages ential inputs, signals common to both inputs are rejected. The
Analog Input AD7626 shows some degradation in THD with higher analog
(IN+ − IN−) Digital Output Code input frequencies.
Description REF = 4.096 V Twos Complement (Hex) 75
FSR − 1 LSB +4.095875V 0x7FFF
Midscale + 1 LSB +125 μV 0x0001 70
Midscale 0V 0x0000
Midscale − 1 LSB −125 μV 0xFFFF 65
−FSR + 1 LSB −4.095875 V 0x8001
CMRR (dB)

−FSR − 4.096 V 0x8000 60

55

50

45
07648-009

1 10 100 1k 10k 100k 1M 10M

INPUT COMMON-MODE FREQUENCY (Hz)

Figure 30. Analog Input CMRR vs. Frequency

Rev. A | Page 16 of 
 AD7626
TYPICAL CONNECTION DIAGRAM

V+ ADR434 8
ADR444

CAPACITOR ON OUTPUT
FOR STABILITY CREF
10µF1
VDD1 10µF1, 2
(5V)
VDD2 100nF
(2.5V)
100nF 32 31 30 29 28 27 26 25

GND

GND
REF

REF

REF

CAP2

CAP2

CAP2
GND 24
1 VDD1
10nF
IN+ 23 IN+
2 VDD2
ADR280 8 PADDLE
IN– 22 IN– SEE THE DRIVING
10µF 3 CAP1 THE AD7625 SECTION7

4 REFIN VCM 21 VCM

VIO AD7626
10kΩ 3 10kΩ
CONTROL FOR 5 EN0 VDD1
VDD1 20
ENABLE FERRITE (5V)
PINS 6 EN1 100nF BEAD6
VDD1 19
VDD2 7 VDD2
(2.5V) VDD2
100nF VDD2 18
(2.5V)
100nF

DCO+
DCO–
CNV+
CNV–

CLK+
CLK–
CONVERSION4
GND
VIO

CONTROL
D+
D–

CMOS (CNV+ ONLY)

OR 8 9 10 11 12 13 14 15 16 17
LVDS CNV+ AND CNV– 5
USING 100Ω
TERMINATION RESISTOR 100Ω
100Ω
VIO
(2.5V)
100Ω 100Ω

DIGITAL INTERFACE SIGNALS

DIGITAL HOST
LVDS TRANSMIT AND RECEIVE

1 SEE THE LAYOUT, DECOUPLING, AND GROUNDING SECTION.

2 CREF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESR AND ESL.
3 USE PULL-UP OR PULL-DOWN RESISTORS TO CONTROL EN0 AND EN1 DURING POWER-UP. EN0 AND EN1 INPUTS CAN BE
FIXED IN HARDWARE OR CONTROLLED USING A DIGITAL HOST (EN0 = 0 AND EN1 = 0 PUTS THE ADC IN POWER-DOWN).
4 OPTION TO USE A CMOS (CNV+) OR LVDS (CNV±) INPUT TO CONTROL CONVERSIONS.
5 TO ENABLE SELF-CLOCKED MODE, TIE DCO+ TO GND.
6 CONNECT PIN 19 AND PIN 20 TO VDD1 SUPPLY; ISOLATE THE TRACE TO PIN 19 AND PIN 20 FROM THE TRACE TO PIN 1 USING A
FERRITE BEAD SIMILAR TO WURTH 74279266.

07648-027
7 SEE THE DRIVING THE AD7626 SECTION FOR DETAILS ON AMPLIFIER CONFIGURATIONS.
8 SEE THE VOLTAGE REFERENCE OPTIONS SECTION FOR DETAILS.

Figure 31. Typical Application Diagram

Rev. A | Page 17 of 
AD7626
DRIVING THE AD7626 ADA4899-1
Differential Analog Input Source
U1
ANALOG INPUT
Figure 33 shows an ADA4899-1 driving each differential input (UNIPOLAR 0V TO 4.096V)
to the AD7626.
Single-Ended-to-Differential Driver 590Ω 20Ω

For applications using unipolar analog signals, a single- 56pF

IN+
ended-to-differential driver (as shown in Figure 32) allows 590Ω
for a differential input into the part. This configuration, when AD7626
provided with an input signal of 0 V to 4.096 V, produces a IN–
differential ±4.096 V with midscale at 2.048 V. The one-pole U2
20Ω VCM

filter using R = 20 Ω and C = 56 pF provides a corner frequency ADA4899-1 56pF

100nF
of 140 MHz. The VCM output of the AD7626 can be buffered 100nF
and then used to provide the required 2.048 V common-mode V+
voltage.
Single-Ended or Fully Differential High Frequency Driver 50Ω

In applications that require higher input frequency tones, the

07648-033
AD8031, AD8032
ADA4932-1 can be used to drive the inputs to the AD7626. The V–
ADA4932-1 is a differential driver, which also allows the user
Figure 32. Single-Ended-to-Differential Driver Circuit Using ADA4899-1
the option of single-ended-to-differential conversion.
Figure 34 shows the typical circuit for a 50 Ω source impedance
(ac-coupled in this example). The input to the ADA4932-1 is
configured to be balanced to the source impedance (in this case
50 Ω). Further information on balancing the input impedance
to the source impedance can be found on the ADA4932-1
datasheet. The circuit shown in Figure 34 operates with an
overall gain of ~0.5 when the termination input termination
is taken into account.
Alternatively, the ADA4932-1 can be used with a fully diffe-
rential source—it acts as an inverting differential driver.

REF1 REF1
CREF CREF
10µF2 10µF2
+VS

20Ω

0V TO VREF 56pF REF REFIN

IN+
ADA4899-1 –VS
AD7626
+VS
IN–
20Ω GND VCM

VREF TO 0V 56pF 2.048V

–VS
ADA4899-1
+VS

VCM

BUFFERED VCM PIN OUTPUT 0.1µF

GIVES THE REQUIRED 2.048V
COMMON-MODE SUPPLY FOR AD8031, AD8032
–VS
ANALOG INPUTS.

1SEE THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS
IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.
07648-025

2C
REF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.
DECOUPLE REF AND REFIN PINS AS PER THE EN1 AND EN0 RECOMMENDATIONS

Figure 33. Driving the AD7626 from a Differential Analog Source Using ADA4899-1

Rev. A | Page 18 of 8
 AD7626
499Ω

SINGLE-ENDED R35
ANALOG INPUT 499Ω
AC-COUPLED C22 C24
AD8031
50Ω SOURCE 53.6Ω +7.25V 0.1µF 0.1µF
GND
GND VDRV+ VCM 100nF
GND GND
56pF

5
6
7
8

9
+VS VOCM 20Ω VCM
1 IN–
2 FB–
C +IN 11
499Ω 3 –OUT
–IN ADA4932-1 10 AD7626
12 +OUT
PD 4
FB+ 20Ω
50Ω 53.6Ω IN+
–VS PAD 56pF

PAD
16
15
14
13
–2.5V
GND GND

C15
0.1µF

07648-130
GND
499Ω

Figure 34. High Frequency Input Drive Circuit Using the ADA4932-1; Single-Ended-to Differential Configuration

Rev. A | Page 19 of 
AD7626
VOLTAGE REFERENCE OPTIONS Table 8. Voltage Reference Options
The AD7626 allows flexible options for creating and buffering Option EN1 EN0 Reference Mode
the reference voltage. The AD7626 conversions refer to 4.096 V A 1 1 Power-up
only. The various options creating this 4.096 V reference are Internal reference and internal
reference buffer in use
controlled by the EN1 and EN0 pins (see Table 8).
B 0 1 External 1.2 V reference applied to
REFIN pin required
C 1 0 External 4.096 V reference applied to
REF pin required.
0 0 Power-down mode

DECOUPLE THE REF AND

REFIN PINS EXTERNALLY.

10µF 10µF

A REF REFIN
IN+

AD7626
IN–

EN1 = 1 AND EN0 = 1

07648-131
POWER-UP—INTERNAL REFERENCE AND REFERENCE BUFFER IN USE.
NO EXTERNAL REFERENCE CIRCUITRY REQUIRED.

Figure 35. Powered Up, Internal Reference and Internal Reference Buffer

1.2V
ADR280 (2.4V ≤ V+ ≥ 5.5V)
CONNECT 1.2V EXTERNAL REFERENCE TO REFIN PIN. VOUT V+ V+
1.2V REFIN INPUT IS BUFFERED INTERNALLY.
IT CREATES A 4.096V REFERENCE FOR THE ADC. 10µF 10µF
0.1µF V– 0.1µF
DECOUPLE THE REF AND REFIN PINS EXTERNALLY

B REF REFIN
IN+

AD7626
IN–

07648-132
EN1 = 0 AND EN0 = 1
EXTERNAL 1.2V REFERENCE CONNECTED TO REFIN PIN IS REQUIRED.

Figure 36. External 1.2 V Reference Using Internal Reference Buffer

V+

ADR434/
(6.1V ≤ VIN ≥ 18V) ADR444 4.096V CONNECT BUFFERED 4.096V SIGNAL TO REF PIN.
VIN VIN VOUT 10µF DECOUPLE THE REF PIN EXTERNALLY.
AD8031 REFIN IS A NO CONNECT.
10µF 0.1µF GND 0.1µF

NO CONNECT

C REF REFIN
IN+

AD7626
IN–
07648-133

EN1 = 1 AND EN0 = 0

EXTERNAL 4.096V REFERENCE CONNECTED TO REF PIN IS REQUIRED.

Figure 37. External 4.096 V Reference Applied to REF Pin

Rev. A | Page 20 of 2
 AD7626
Wake-Up Time from EN1= 0, EN0 = 0 Power-Up
The AD7626 powers down when EN1 and EN0 are both set to When powering up the AD7626 device, first apply the 2.5 V
0. Selecting the correct reference choice from power-down, the VDD2 supply and VIO voltage to the device. After the VIO and
user sets EN1 and EN0 to the required value shown in Table 8. 2.5 V VDD2 have been established, apply the 5 V VDD1 supply.
The user may immediately apply CNV pulses to receive data If using an external reference with the AD7626, ensure that the
conversion results. Typical wake-up times for the selected EN0 and EN1 pins are connected to the correct logic values
reference settings are shown in Table 9. Each time represents associated with the reference option of choice and then apply
the duration from the EN1, EN0 logic transition to when the the external reference voltage. Finally, apply the analog inputs to
output of the ADC is settled to 0.5 LSB accuracy. the ADC.
25
VDD2 INTERNAL
Table 9. Wake-Up Time from EN1=0, EN0 = 0 REFERENCE
Wake-Up
20
Time (0.5 LSB VDD2 EXTERNAL
REFERENCE
Reference Mode EN1 EN0 Accuracy) VIO INTERNAL

CURRENT (mA)
REFERENCE
A Power-up 1 1 9.5 sec 15
Internal reference and inter- VIO EXTERNAL
nal reference buffer in use REFERENCE
10
B External 1.2 V reference 0 1 25 ms
applied to REFIN pin VDD1 INTERNAL
REFERENCE
C External 4.096 V reference 1 0 65 μs 5
applied to REF pin VDD1 EXTERNAL
REFERENCE

0
POWER SUPPLY

07648-235
0 2 4 6 8 10
THROUGHPUT (MSPS)
The AD7626 uses both 5 V (VDD1) and 2.5 V (VDD2) power
supplies, as well as a digital input/output interface supply (VIO). Figure 39. Current Consumption vs. Sampling Rate
VIO allows a direct interface with 2.5 V logic only. VIO and
VDD2 can be taken from the same 2.5 V source; however, it is 160
best practice to isolate the VIO and VDD2 pins using separate
140
traces as well as to decouple each pin separately. INTERNAL REFERENCE
120
The 5 V and 2.5 V supplies required for the AD7626 can be
EXTERNAL REFERENCE
generated using Analog Devices, Inc., LDOs such as 100
POWER (mW)

the ADP3330-2.5, ADP3330-5, ADP3334, and ADP1708.

80
90
VDD2
60
85

40
80
VDD1
20
75
PSRR (dB)

07648-236
70 0 1 2 3 4 5 6 7 8 9 10
THROUGHPUT (MSPS)
65
Figure 40. Power Dissipation vs. Sampling Rate
60

55
INTERNAL REFERENCE USED
50
07648-011

1 10 100 1k 10k
SUPPLY FREQUENCY (Hz)

Figure 38. PSRR vs. Supply Frequency

(350 mV pp Ripple on VDD2, 600 mV Ripple on VDD1)

Rev. A | Page 21 of 2
AD7626
DIGITAL INTERFACE The clock DCO± is a buffered copy of CLK± and is synchronous
Conversion Control to the data, D±, which is updated on the falling edge of DCO +
(tD). By maintaining good propagation delay matching between
All analog-to-digital conversions are controlled by the CNV±
D± and DCO± through the board and the digital host, DCO
signal. This signal can be applied in the form of a CNV+/CNV−
can be used to latch D± with good timing margin for the shift
LVDS signal, or it can be applied in the form of a 2.5 V CMOS
register.
logic signal to the CNV+ pin. The conversion is initiated by the
rising edge of the CNV± signal. Conversions are initiated by a rising edge CNV± pulse. The
CNV± pulse must be returned low (≤ tCNVH maximum) for
After the AD7626 is powered up, the first conversion result
valid operation. After a conversion begins, it continues until
generated is invalid. Subsequent conversion results are valid
completion. Additional CNV± pulses are ignored during the
provided that the time between conversions does not exceed
conversion phase. After the time, tMSB, elapses, the host should
the maximum specification for tCYC.
begin to burst the CLK±. Note that, tMSB, is the maximum time
The two methods for acquiring the digital data output of the for the MSB of the new conversion result and should be used as
AD7626 via the LVDS interface are described in the following the gating device for CLK±. The echoed clock, DCO±, and the
sections. data, D, are driven in phase with D± being updated on the
Echoed-Clock Interface Mode falling edge of DCO+; the host should use the rising edge of
DCO+ to capture D±. The only requirement is that the 16
The digital operation of the AD7626 in echoed-clock interface
CLK± pulses finish before the time (tCLKL) elapses of the next
mode is shown in Figure 41. This interface mode, requiring
conversion phase or the data is lost. From the tCLKL to tMSB, D±
only a shift register on the digital host, can be used with many
and DCO± are driven to 0. Set CLK± to idle low between CLK±
digital hosts (such as FPGA, shift register, and microprocessor).
bursts.
It requires three LVDS pairs (D±, CLK±, and DCO±) between
each AD7626 and the digital host.

SAMPLE N SAMPLE N + 1
tCYC

tCNVH

CNV–

CNV+

ACQUISITION ACQUISITION ACQUISITION

tCLKL
tCLK
15 16 1 2 15 16 1 2 3
CLK–

CLK+
tDCO
15 16 1 2 15 16 1 2 3
DCO–

DCO+
tMSB tD
tCLKD
D+
07648-103

D1 D0 D15 D14 D1 D0 0 D15 D14 D13

N–1 N–1 0 N N N N N+1 N+1 N+1
D–

Figure 41. Echoed-Clock Interface Mode Timing Diagram

Rev. A | Page 22 of 2
 AD7626
Self-Clocked Mode The AD7626 data captured on each phase of the state
The digital operation of the AD7626 in self-clocked interface machine clock is then compared. The location of the 1 in
mode is shown in Figure 42. This interface mode reduces the the header in each set of data acquired allows the user to
number of traces between the ADC and the digital host to two choose the state machine clock phase that occurs during
LVDS pairs (CLK± and D±) or to a single pair if sharing a the data valid window of D±.
common CLK±. Multiple AD7626 devices can share a common The self-clocked mode data capture method allows the digital
CLK± signal. This can be useful in reducing the number of host to adapt its result capture timing to accommodate
LVDS connections to the digital host. variations in propagation delay through any AD7626.For
When the self-clocked interface mode is used, each ADC example, where data is captured from multiple AD7626s
data-word is preceded by a 010 sequence. The first zero is sharing a common input clock.
automatically on D± once tMSB has elapsed. The 2-bit header Conversions are initiated by a CNV± pulse. The CNV± pulse
is then clocked out by the first two CLK± falling edges. This must be returned low (tCNVH maximum) for valid operation.
header is used to synchronize D± of each conversion in the After a conversion begins, it continues until completion.
digital host because, in this mode, there is no data clock output Additional CNV± pulses are ignored during the conversion
synchronous to the data (D±) to allow the digital host to phase. After the time, tMSB, elapses, the host begins to burst
acquire the data output. the CLK± signal to the AD7626. All 18 CLK± pulses are to be
Synchronization of the D± data to the digital host’s acquisition applied in the time window framed by tMSB and the subsequent
clock is accomplished by using one state machine per AD7626 tCLKL. The required 18 CLK± pulses must finish before tCLKL
device. For example, using a state machine that runs at the (referenced to the next conversion phase) elapses. Otherwise,
same speed as CLK± incorporates three phases of this clock the data is lost because it is overwritten by the next conversion
frequency (120º apart). Each phase acquires the data D± as result.
output by the ADC. Set CLK± to idle high between bursts of 18 CLK± pulses. The
header bit and conversion data of the next ADC result are
output on subsequent falling edges of CLK± during the next
burst of the CLK± signal.

SAMPLE N SAMPLE N + 1
tCYC

tCNVH

CNV–

CNV+

ACQUISITION ACQUISITION ACQUISITION

tCLK tCLKL

17 18 1 2 3 4 17 18 1 2 3
CLK–

CLK+
tMSB
tCLKD
D+
07648-104

D1 D0 D15 D14 D1 D0 D15

0 1 0 0 1 0 N+1
N–1 N–1 N N N N
D–

Figure 42. Self-Clocked Interface Mode Timing Diagram

Rev. A | Page 23 of 2
AD7626

APPLICATIONS INFORMATION
LAYOUT, DECOUPLING, AND GROUNDING VIO Supply Decoupling
When laying out the printed circuit board (PCB) for the AD7626, Decouple the VIO supply applied to Pin 12 to ground at Pin 13.
follow the practices described in this section to obtain the maxi- Layout and Decoupling of Pin 25 to Pin 32
mum performance from the converter. Connect the outputs of Pin 25, Pin 26, and Pin 28 together and
Exposed Paddle decouple them to Pin 27 using a 10 μF capacitor with low ESR
The AD7626 has an exposed paddle on the underside of the and low ESL.
package. Reduce the inductance of the path connecting Pin 25, Pin 26,
and Pin 28 by widening the PCB traces connecting these pins.
• Solder the paddle directly to the PCB.
• Connect the paddle to the ground plane of the board using Take a similar approach in the connections used for the
multiple vias, as shown in Figure 43. reference pins of the AD7626. Connect Pin 29, Pin 30, and
• Decouple all supply pins except for Pin 12 (VIO) directly to Pin 32 together using widened PCB traces to reduce inductance.
the paddle, minimizing the current return path. In internal or external reference mode, a 4.096 V reference voltage
• Pin 13 and Pin 24 can be connected directly to the paddle. is output on Pin 29, Pin 30, and Pin 32. Decouple these pins to
Use vias to ground at the point where these pins connect to Pin 31 using a 10 μF capacitor with low ESR and low ESL.
the paddle. Figure 43 shows an example of the recommended layout for
the underside of the AD7626 device. Note the extended signal
VDD1 Supply Routing and Decoupling
trace connections and the outline of the capacitors decoupling
The VDD1 supply is connected to Pin 1, Pin 19, and Pin 20. the signals applied to the REF pins (Pin 29, Pin 30, and Pin 32)
Decouple the supply using a 100 nF capacitor at Pin 1. The user and to the CAP2 pins (Pin 25, Pin 26, and Pin 28).
can connect this supply trace to Pin 19 and Pin 20. Use a series
ferrite bead to connect the VDD1 supply from Pin 1 to Pin 19
and Pin 20. The ferrite bead isolates any high frequency noise or
ringing on the VDD1 supply. Decouple the VDD1 supply to Pin
19 and Pin 20 using a 100 nF capacitor decoupled to ground at
the exposed paddle.

24 23 22 21 20 19 18 17

25 16
26 PADDLE
15
4.096V
EXTERNAL REFERENCE 27 14
(ADR434 OR ADR444) 28 13
29 12
30 11
31 10
32 9

1 2 3 4 5 6 7 8
07648-013

Figure 43. PCB Layout and Decoupling Recommendations for Pin 24 to Pin 32

Rev. A | Page 24 of 2
 AD7626

OUTLINE DIMENSIONS
5.00 0.60 MAX
BSC SQ 0.60 MAX PIN 1
INDICATOR
25 32
24 1
PIN 1
INDICATOR 0.50
TOP 4.75 BSC EXPOSED 3.25
VIEW BSC SQ PAD 3.10 SQ
(BOTTOM VIEW) 2.95
0.50
0.40 17 8
16 9
0.30
0.25 MIN
0.80 MAX 3.50 REF
12° MAX 0.65 TYP

0.05 MAX FOR PROPER CONNECTION OF

1.00 0.02 NOM THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
0.85 0.30 FUNCTION DESCRIPTIONS
COPLANARITY
0.80 0.23 0.20 REF SECTION OF THIS DATA SHEET.
SEATING 0.08
PLANE 0.18

011708-A
COMPLIANT TO JEDEC STANDARDS MO-220-VHHD-2

Figure 44. 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]

5 mm × 5 mm Body, Very Thin Quad
(CP-32-2)
Dimensions shown in millimeters

ORDERING GUIDE
Model 1 Temperature Range Package Description Package Option
AD7626BCPZ −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-2
AD7626BCPZ-RL7 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-2
EVAL-AD7626EDZ 2 Evaluation Board
EVAL-CED1Z 3 Converter Evaluation and Development Board
1
Z = RoHS Compliant Part.
2
This board can be used as a standalone evaluation board or in conjunction with the EVAL-CEDIZ for evaluation/demonstration purposes.
3
This board allows the PC to control and communicate with all Analog Devices evaluation boards with model numbers ending with the ED designator.

Rev. A | Page 25 of 2
AD7626

NOTES

Rev. A | Page 26 of 2
 AD7626

NOTES

Rev. A | Page 27 of 2
AD7626

NOTES

©2009–2010 Analog Devices, Inc. All rights reserved. Trademarks and

registered trademarks are the property of their respective owners.
D07648-0-1/10(A)

Rev. A | Page 28 of 28