AD AD7984 16-bit, 6 msps, pulsar differential adc Datasheet

16-Bit, 6 MSPS, PulSAR
Differential ADC
AD7625
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
APPLICATIONS
High dynamic range telecommunications
Receivers
Digital imaging systems
High speed data acquisition
Spectrum analysis
Test equipment
REFIN
REF VCM
1.2V
BAND GAP
IN+
VIO
CLOCK
÷2
LOGIC
CAP
DAC
IN–
CNV+, CNV–
D+, D–
SAR
AD7625
SERIAL
LVDS
DCO+, DCO–
CLK+, CLK–
07652-001
Throughput: 6 MSPS
SNR: 93 dB
INL: ±0.45 LSB typical, ±1 LSB maximum
DNL: ±0.3 LSB typical, ±0.5 LSB maximum
Power dissipation: 135 mW
32-lead LFCSP (5 mm × 5 mm)
SAR architecture
No latency/no pipeline delay
16-bit resolution with no missing codes
Zero error: ±1.5 LSB
Differential input voltage: ±4.096 V
Serial LVDS interface
Self-clocked mode
Echoed-clock mode
Can use LVDS or CMOS for conversion control (CNV signal)
Reference options
Internal: 4.096 V
External (1.2 V) buffered to 4.096 V
External: 4.096 V
Figure 1.
GENERAL DESCRIPTION
The AD7625 is a 16-bit, 6 MSPS, charge redistribution successive
approximation register (SAR) based architecture analog-to-digital
converter (ADC). SAR architecture allows unmatched performance both in noise (93 dB SNR) and in linearity (1 LSB). The
AD7625 contains a high speed, 16-bit sampling ADC, an internal
conversion clock, and an internal buffered reference. On the
CNV± rising edge, it samples the voltage difference between the
IN+ and IN− pins. The voltages on these pins swing in opposite
phase between 0 V and REF. The 4.096 V reference voltage, REF,
can be generated internally or applied externally.
All converted results are available on a single LVDS self-clocked
or echoed-clock serial interface, reducing external hardware
connections.
The AD7625 is housed in a 32-lead, 5 mm × 5 mm LFCSP with
operation specified from −40°C to +85°C.
Table 1. Fast PulSAR® ADC Selection
Input Type
Differential (Ground Sense)
True Bipolar
Differential (Antiphase)
Resolution (Bits)
16
16
16
16
16
16
16
18
18
18
1 MSPS to <2 MSPS
AD7653
AD7667
AD7980
AD7983
AD7671
AD7677
AD7623
AD7643
AD7982
AD7984
2 MSPS to 3 MSPS
6 MSPS
AD7621
AD7622
AD7641
AD7625
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
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2009–2012 Analog Devices, Inc. All rights reserved.
AD7625
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Circuit Information .................................................................... 13
Applications ....................................................................................... 1
Converter Information .............................................................. 13
Functional Block Diagram .............................................................. 1
Transfer Functions ..................................................................... 14
General Description ......................................................................... 1
Analog Inputs.............................................................................. 14
Revision History ............................................................................... 2
Typical Connection Diagram ................................................... 15
Specifications..................................................................................... 3
Driving the AD7625................................................................... 16
Timing Specifications .................................................................. 5
Voltage Reference Options ........................................................ 17
Absolute Maximum Ratings ............................................................ 6
Power Supply............................................................................... 18
Thermal Resistance ...................................................................... 6
Digital Interface .......................................................................... 19
ESD Caution .................................................................................. 6
Applications Information .............................................................. 21
Pin Configuration and Function Descriptions ............................. 7
Layout, Decoupling, and Grounding ....................................... 21
Typical Performance Characteristics ............................................. 9
Outline Dimensions ....................................................................... 22
Terminology .................................................................................... 12
Ordering Guide .......................................................................... 22
Theory of Operation ...................................................................... 13
REVISION HISTORY
7/12—Rev. 0 to Rev. A
Change to Table 5 .......................................................................................... 6
Changes to Figure 2 ...................................................................................... 7
Updated Outline Dimensions (Changed CP-32-2 to CP-32-7) .....22
Changes to Ordering Guide ...........................................................22
1/09—Revision 0: Initial Version
Rev. A | Page 2 of 24
Data Sheet
AD7625
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
RESOLUTION
ANALOG INPUT
Voltage Range
Operating Input Voltage
Common-Mode Input Range
Common-Mode Rejection Ratio
Input Current
THROUGHPUT
Complete Cycle
Throughput Rate
DC ACCURACY
Integral Linearity Error
No Missing Codes
Differential Linearity Error
Transition Noise
Zero Error
Zero Error Drift
Gain Error
Gain Error Drift
Power Supply Sensitivity 1
AC ACCURACY
External Reference
Dynamic Range
Signal-to-Noise Ratio
Spurious-Free Dynamic Range
Total Harmonic Distortion
Signal-to-(Noise + Distortion)
Internal Reference
Dynamic Range
Signal-to-Noise Ratio
Spurious-Free Dynamic Range
Total Harmonic Distortion
Signal-to-(Noise + Distortion)
−3 dB Input Bandwidth
Aperture Jitter
INTERNAL REFERENCE
Output Voltage
Temperature Drift
REFERENCE BUFFER
REFIN Input Voltage Range
REF Output Voltage Range
Line Regulation
EXTERNAL REFERENCE
Voltage Range
VCM PIN
Output Voltage
Output Impedance
Test Conditions/Comments
Min
16
VIN+ − VIN−
VIN+, VIN− to GND
−VREF
−0.1
VREF/2 − 0.05
fIN = 1 MHz
Midscale input
Typ
Max
Unit
Bits
+VREF
VREF + 0.1
VREF/2 + 0.05
V
V
V
dB
µA
166
6
ns
MSPS
±0.45
+1
±0.3
0.6
±1.5
0.5
8
0.4
0.4
0.2
+0.5
LSB
Bits
LSB
LSB
LSB
ppm/°C
LSB
ppm/°C
LSB
LSB
VREF/2
60
77
0.1
−1
16
−0.5
TMIN to TMAX
−4
TMIN to TMAX
VDD1 = 5 V ± 5%
VDD2 = 2.5 V ± 5%
+4
20
fIN = 20 kHz
92.5
92
91.5
93.2
93
106
−105.5
92
dB
dB
dB
dB
dB
93.2
92.9
106
−105.5
92.5
100
0.25
dB
dB
dB
dB
dB
MHz
ps rms
1.2
±15
V
ppm/°C
fIN = 20 kHz
92.5
91.5
91
REFIN @ 25°C
−40°C to +85°C
4.076
VDD1 ± 5%, VDD2 ± 5%
REF
@ 25°C
1.2
4.096
5
4.116
4.096
4
Rev. A | Page 3 of 24
REF/2
5
V
V
mV
V
6
V
kΩ
AD7625
Parameter
LVDS I/O (ANSI-644)
Data Format
Differential Output Voltage, VOD
Common-Mode Output Voltage, VOCM 2
Differential Input Voltage, VID
Common-Mode Input Voltage, VICM
POWER SUPPLIES
Specified Performance
VDD1
VDD2
VIO
Operating Currents
Static—Not Converting
VDD1
VDD2
VIO
With Internal Reference
VDD1
VDD2
VIO
Without Internal Reference
VDD1
VDD2
VIO
Power Dissipation 3
Static—Not Converting
With Internal Reference
Without Internal Reference
Energy per Conversion
TEMPERATURE RANGE
Specified Performance
1
2
3
Data Sheet
Test Conditions/Comments
Min
RL = 100 Ω
RL = 100 Ω
200
850
100
800
4.75
2.37
2.37
Self-clocked mode and echoedclock mode
6 MSPS throughput
Self-clocked mode and echoedclock mode
6 MSPS throughput
Self-clocked mode and echoedclock mode
6 MSPS throughput
6 MSPS throughput
6 MSPS throughput
TMIN to TMAX
−40
Typ
Max
Serial LVDS twos complement
350
454
1250
1375
650
1575
Unit
mV
mV
mV
mV
5
2.5
2.5
5.25
2.63
2.63
V
V
V
4.5
17
11
7.8
22.7
13
mA
mA
mA
11
21.5
13.5
15.4
28.3
16
mA
mA
mA
9
21
13.5
12.1
26
16
mA
mA
mA
95
145
135
22
130
190
165
mW
mW
mW
nJ/sample
+85
°C
Using an external reference.
The ANSI-644 LVDS specification has a minimum output common mode (VOCM) of 1125 mV.
Power dissipation is for the AD7625 device only. In self-clocked interface mode, 9 mW is dissipated in the 100 Ω terminator. In echoed-clock interface mode, 18 mW is
dissipated in two 100 Ω terminators.
Rev. A | Page 4 of 24
Data Sheet
AD7625
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
Time Between Conversions 1
Acquisition Time
CNV± High Time
CNV± to D± (MSB) Delay
CNV± to Last CLK± (LSB) Delay
CLK± Period 2
CLK± Frequency
CLK± to DCO± Delay (Echoed-Clock Mode)
DCO± to D± Delay (Echoed-Clock Mode)
CLK± to D± Delay
1
2
Symbol
tCYC
tACQ
tCNVH
tMSB
tCLKL
tCLK
fCLK
tDCO
tD
tCLKD
Min
166
40
10
Typ
(tCYC − tMSB + tCLK)/n
4
250
4
0
4
0
0
Max
10,000
40
145
110
3.33
300
7
1
7
Unit
ns
ns
ns
ns
ns
ns
MHz
ns
ns
ns
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.
For the minimum CLK period, the window available to read data is tCYC − tMSB + tCLK. Divide this time by the number of bits (n) that are read. In echoed-clock interface
mode, n = 16; in self-clocked interface mode, n = 18.
Rev. A | Page 5 of 24
AD7625
Data Sheet
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 4.
Parameter
Analog Inputs/Outputs
IN+, IN− to GND1
2
REF to GND
VCM, CAP2 to GND
CAP1, REFIN to GND
Supply Voltage
VDD1
VDD2, VIO
Digital Inputs to GND
Digital Outputs to GND
Input Current to Any Pin Except
Supplies3
Operating Temperature Range
(Commercial)
Storage Temperature Range
Junction Temperature
ESD
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Rating
−0.3 V to REF + 0.3 V or
±130 mA
−0.3 V to +6 V
−0.3 V to +6 V
−0.3 V to +2.7 V
Table 5. Thermal Resistance
Package Type
32-Lead LFCSP_WQ
ESD CAUTION
−0.3 V to +6 V
−0.3 V to +3 V
−0.3 V to VIO + 0.3 V
−0.3 V to VIO + 0.3 V
±10 mA
−40°C to +85°C
−65°C to +150°C
150°C
1 kV
1
See the Analog Inputs section.
Keep CNV+/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.
2
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 6 of 24
θJA
40
θJC
4
Unit
°C/W
Data Sheet
AD7625
32
31
30
29
28
27
26
25
REF
GND
REF
REF
CAP2
GND
CAP2
CAP2
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
AD7625
TOP VIEW
(Not to Scale)
24
23
22
21
20
19
18
17
GND
IN+
IN–
VCM
VDD1
VDD1
VDD2
CLK+
NOTES
1. CONNECT THE EXPOSED PAD TO THE GROUND
PLANE OF THE PCB USING MULTIPLE VIAS.
07652-002
CNV+
D–
D+
VIO
GND
DCO–
DCO+
CLK–
9
10
11
12
13
14
15
16
VDD1
VDD2
CAP1
REFIN
EN0
EN1
VDD2
CNV–
Figure 2.
Table 6. Pin Function Descriptions
Pin No.
1
2
Mnemonic
VDD1
VDD2
Type1
P
P
3
4
CAP1
REFIN
AO
AI/O
5, 6
EN0, EN1
DI
7
8, 9
VDD2
CNV−, CNV+
P
DI
10, 11
12
13
14, 15
D−, D+
VIO
GND
DCO−, DCO+
DO
P
P
DO
16, 17
18
19, 20
CLK−, CLK+
VDD2
VDD1
DI
P
P
21
VCM
AO
22
23
24
IN−
IN+
GND
AI
AI
P
Description
Analog 5 V Supply. Decouple the 5 V supply with a 100 nF capacitor.
Analog 2.5 V Supply. Decouple this pin with a 100 nF capacitor. The 2.5 V supply source should
supply this pin first and then be traced to the other VDD2 pins (Pin 7 and Pin 18).
Connect this pin to a 10 nF capacitor.
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.
Enable Pins. The logic levels of these pins set the operation of the device as follows:
EN1 = 0, EN0 = 0: Illegal state.
EN1 = 0, EN0 = 1: Enable internal buffer, disable internal reference. An external 1.2 V reference
connected to the REFIN pin is required.
EN1 = 1, EN0 = 0: Disable internal reference and reference buffer. An external 4.096 V reference
connected to the REF pin is required.
EN1 = 1, EN0 = 1: Enable internal reference and reference buffer.
Digital 2.5 V Supply. Decouple this pin with a 100 nF capacitor.
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.
LVDS Data Outputs. The conversion data is output serially on these pins.
Input/Output Interface Supply. Use a 2.5 V supply and decouple this pin with a 100 nF capacitor.
Ground. Return path for the 100 nF capacitor connected to Pin 12.
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 a 2-bit header (10) to allow synchronization of
the data by the digital host with simple logic. 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 latched in the digital host on the next rising edge of DCO+.
LVDS Clock Inputs. This clock shifts out the conversion results on the falling edge of CLK+.
Analog 2.5 V Supply. Decouple this pin with a 100 nF capacitor.
Analog 5 V Supply. Isolate these pins from Pin 1 with a ferrite bead and decouple them with a 100 nF
capacitor.
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.
Differential Negative Analog Input. Referenced to and must be driven 180° out of phase with IN+.
Differential Positive Analog Input. Referenced to and must be driven 180° out of phase with IN−.
Ground.
Rev. A | Page 7 of 24
AD7625
Data Sheet
Pin No.
25, 26, 28
Mnemonic
CAP2
Type 1
AO
27
29, 30, 32
GND
REF
P
AI/O
31
EP
GND
Exposed Pad
P
1
Description
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).
Ground. Return path for the 10 μF capacitor connected to Pin 25, Pin 26, and Pin 28.
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).
Ground. Return path for the 10 μF capacitor connected to Pin 29, Pin 30, and Pin 32.
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.
AI = analog input; AI/O = bidirectional analog; AO = analog output; DI = digital input; DO = digital output; P = power.
Rev. A | Page 8 of 24
Data Sheet
AD7625
0
–20
–20
–40
–40
–60
–60
–80
–100
–120
–100
–120
–140
–160
–160
0
0.5
1.0
1.5
2.0
2.5
3.0
FREQUENCY (MHz)
–180
0
10
15
20
25
30
35
40
45
Figure 6. FFT 2 kHz Input Tone, Zoom In on Input Tone and Harmonics
0
INPUT TONE = 50kHz
SNR = 93.04dB
SINAD = 92.63dB
THD = –103.57dB
SFDR = –102.69dB
–40
–40
AMPLITUDE (dB)
–60
–80
–100
–120
–60
–80
–100
–120
–140
–140
–160
–160
0
0.5
1.0
1.5
2.0
2.5
3.0
FREQUENCY (MHz)
–180
07652-007
–180
INPUT TONE = 100kHz
SNR = 92.91dB
SINAD = 92.55dB
THD = –103.11dB
SFDR = –103.41dB
–20
0
0.4
0.8
0.3
0.6
0.2
0.4
0.1
0.2
INL (LSB)
1.0
0
–0.1
–0.6
–0.4
–0.8
–0.5
65,536
07652-015
–0.3
CODE
2.5
3.0
0
–0.4
49,152
2.0
–0.2
–0.2
32,768
1.5
Figure 7. FFT 100 kHz Input Tone
0.5
16,384
1.0
FREQUENCY (MHz)
Figure 4. FFT 50 kHz Input Tone
0
0.5
Figure 5. Differential Nonlinearity vs. Code
–1.0
0
16,384
32,768
49,152
CODE
Figure 8. Integral Nonlinearity vs. Code
Rev. A | Page 9 of 24
65,536
07652-014
–20
07652-008
0
DNL (LSB)
5
FREQUENCY (kHz)
Figure 3. FFT 2 kHz Input Tone, Full View
AMPLITUDE (dB)
–80
–140
–180
INPUT TONE = 2kHz
SNR = 93.16dB
SINAD = 92.09dB
THD = –110.45dB
SFDR = 111.37dB
07652-006
AMPLITUDE (dB)
0
07652-005
AMPLITUDE (dB)
TYPICAL PERFORMANCE CHARACTERISTICS
AD7625
Data Sheet
–94
–100.5
–96
–0.5dBFS
–101.0
–98
–100
INTERNAL REF
–3dBFS
THD (dB)
THD (dB)
–101.5
–1dBFS
–102
–104
–106
–102.0
–10dBFS
–108
–102.5
EXTERNAL REF
–110
–5dBFS
–112
–103.0
0
20
40
60
80
100
120
INPUT FREQUENCY (kHz)
–103.5
–60
07652-012
–116
0
20
40
60
80
100
120
Figure 12. THD vs. Temperature (−0.5 dB, 20 kHz Input Tone)
93.2
93.8
93.0
93.6
DYNR vs. TEMP INTERNAL REF
DYNR vs. TEMP EXTERNAL REF
93.4
92.8
SINAD vs. TEMP EXTERNAL REF
SINAD (dB)
93.2
93.0
92.8
SNR vs. TEMP EXTERNAL REF
SNR vs. TEMP INTERNAL REF
92.6
92.6
92.4
92.2
SINAD vs. TEMP INTERNAL REF
92.0
–40
–20
0
20
40
60
80
100
120
TEMPERATURE (°C)
91.6
–60
07652-018
–40
0
20
40
60
80
100
120
100
120
TEMPERATURE (°C)
Figure 10. Dynamic Range and SNR vs. Temperature
(−0.5 dB, 20 kHz Input Tone)
Figure 13. SINAD vs. Temperature
(−0.5 dB, 20 kHz Input Tone)
12
120
ZERO ERROR AND GAIN ERROR (LSB)
100
80
IN+
60
40
20
IN–
0
–20
–4
–2
0
2
DIFFERENTIAL INPUT VOLTAGE (V)
4
6
07652-010
–40
–60
–6
–20
Figure 11. Input Current (IN+, IN−) vs. Differential Input Voltage (6 MSPS)
Rev. A | Page 10 of 24
10
8
GAIN ERROR
6
4
2
ZERO ERROR
0
–60
–40
–20
0
20
40
60
80
TEMPERATURE (°C)
Figure 14. Zero Error and Gain Error vs. Temperature
07652-020
92.2
–60
07652-019
91.8
92.4
INPUT CURRENT (µA)
–20
TEMPERATURE (°C)
Figure 9. THD at Input Amplitudes of −0.5 dBFS to −10 dBFS vs. Frequency
SNR, DYNAMIC RANGE (dB)
–40
07652-021
–114
Data Sheet
AD7625
140,000
250,000
262,144 SAMPLES
STD DEVIATION = 0.4829
128,084
129,601 262,144 SAMPLES
STD DEVIATION = 0.5329
FEC8
FEC9
120,000
201,320
200,000
100,000
COUNT
COUNT
150,000
100,000
80,000
60,000
40,000
50,000
0
FEC7
54
FEC8
20,000
46
FEC9
FECA
FECB
FECC
0
FECD
CODE (HEX)
07652-022
0
30,073
Figure 15. Histogram of 262,144 Conversions of a DC Input
at the Code Center (Internal Reference)
262,144 SAMPLES
STD DEVIATION = 0.4814
201,614
COUNT
150,000
100,000
50,000
0
0
41
FEC8
FEC9
FECA
FECB
FECC
33
0
FECD
FECE
CODE (HEX)
07652-024
30,250
30,206
0
FEC6
2329
2130
FEC7
FECA
0
FECB
CODE (HEX)
Figure 17. Histogram of 262,144 Conversions of a DC Input
at the Code Transition (Internal Reference)
250,000
200,000
0
Figure 16. Histogram of 262,144 Conversions of a DC Input
at the Code Center (External Reference)
Rev. A | Page 11 of 24
07652-023
30,651
AD7625
Data Sheet
TERMINOLOGY
Common-Mode Rejection Ratio (CMRR)
CMRR is defined as the ratio of the power in the ADC output at
full-scale frequency, f, to the power of an 80 mV p-p sine wave
applied to the common-mode voltage of VIN+ and VIN− at
frequency fS.
CMRR (dB) = 10log(Pf/PfS)
Power Supply Rejection Ratio (PSRR)
Variations in power supply affect the full-scale transition but not
the linearity of the converter. PSRR is the maximum change in
the full-scale transition point due to a change in power supply
voltage from the nominal value.
Reference Voltage Temperature Coefficient
The reference voltage temperature coefficient is derived from the
typical shift of output voltage at 25°C on a sample of parts at the
maximum and minimum reference output voltage (VREF) measured at TMIN, T(25°C), and TMAX. It is expressed in ppm/°C as
where:
Pf is the power at frequency f in the ADC output.
PfS is the power at frequency fS in the ADC output.
Differential Nonlinearity (DNL) Error
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It
is often specified in terms of resolution for which no missing
codes are guaranteed.
Integral Nonlinearity (INL) Error
Linearity error refers to the deviation of each individual code
from a line drawn from negative full scale through positive full
scale. The point used as negative full scale occurs ½ LSB before
the first code transition. Positive full scale is defined as a level
1½ LSB beyond the last code transition. The deviation is measured from the middle of each code to the true straight line.
Dynamic Range
Dynamic range is the ratio of the rms value of the full scale to
the rms noise measured for an input typically at −60 dB. The
value for dynamic range is expressed in decibels.
Effective Number of Bits (ENOB)
ENOB is a measurement of the resolution with a sine wave
input. It is related to SINAD and is expressed in bits by
TCVREF ( ppm/°C ) =
× 10 6
where:
VREF (Max) = maximum VREF at TMIN, T(25°C), or TMAX.
VREF (Min) = minimum VREF at TMIN, T(25°C), or TMAX.
VREF (25°C) = VREF at 25°C.
TMAX = +85°C.
TMIN = −40°C.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Signal-to-(Noise + Distortion) (SINAD) Ratio
SINAD is the ratio of the rms value of the actual input signal to
the rms sum of all other spectral components below the Nyquist
frequency, including harmonics but excluding dc. The value for
SINAD is expressed in decibels.
Spurious-Free Dynamic Range (SFDR)
ENOB = [(SINADdB − 1.76)/6.02]
SFDR is the difference, in decibels, between the rms amplitude
of the input signal and the peak spurious signal.
Gain Error
The first transition (from 100 … 000 to 100 …001) should occur
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
011 … 111) should occur for an analog voltage 1½ LSB below
the nominal full scale (+4.0959375 V for the ±4.096 V range).
The gain error is the deviation of the difference between the
actual level of the last transition and the actual level of the first
transition from the difference between the ideal levels.
Least Significant Bit (LSB)
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of the first five harmonic
components to the rms value of a full-scale input signal and
is expressed in decibels.
Zero Error
Zero error is the difference between the ideal midscale input
voltage (0 V) and the actual voltage producing the midscale
output code.
The least significant bit, or LSB, is the smallest increment that
can be represented by a converter. For a fully differential input
ADC with N bits of resolution, the LSB expressed in volts is
LSB (V) =
VREF ( Max ) – VREF ( Min)
VREF ( 25°C ) × ( TMAX – TMIN )
V INp-p
2N
Rev. A | Page 12 of 24
Data Sheet
AD7625
THEORY OF OPERATION
IN+
GND
LSB
MSB
32,768C 16,384C
4C
2C
SWITCHES
CONTROL
SW+
C
C
REF
(4.096V)
CLK+, CLK–
COMP
GND
4C
2C
C
DATA TRANSFER
D+, D–
OUTPUT CODE
C
MSB
DCO+, DCO–
SW–
LSB
CNV+, CNV–
GND
CONVERSION
CONTROL
IN–
LVDS INTERFACE
07652-030
32,768C 16,384C
CONTROL
LOGIC
Figure 18. ADC Simplified Schematic
CIRCUIT INFORMATION
The AD7625 is a 6 MSPS, high precision, power efficient, 16-bit
ADC that uses SAR based architecture to provide performance
of 93 dB SNR, ±0.45 LSB INL, and ±0.3 LSB DNL.
The AD7625 is capable of converting 6,000,000 samples per
second (6 MSPS). The device typically consumes 135 mW. The
AD7625 offers the added functionality of a high performance
on-chip reference and on-chip reference buffer.
The AD7625 is specified for use with 5 V and 2.5 V supplies
(VDD1, VDD2). The interface from the digital host to the
AD7625 uses 2.5 V logic only. The AD7625 uses an LVDS
interface to transfer data conversions. The CNV+ and CNV−
inputs to the part activate the conversion of the analog input.
The CNV+ and CNV− pins can be applied using a CMOS or
LVDS source.
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 inputs (IN+ and IN−) captured at the end
of the acquisition phase is applied to the comparator inputs,
causing the comparator to become unbalanced. By switching
each element of the capacitor array between GND and 4.096 V
(the reference voltage), the comparator input varies by binary
weighted voltage steps (VREF/2, VREF/4 … VREF/65,536). The
control logic toggles these switches, MSB first, to bring the
comparator back into a balanced condition. At the completion
of this process, the control logic generates the ADC output code.
The AD7625 digital interface uses low voltage differential
signaling (LVDS) to enable high data transfer rates.
CONVERTER INFORMATION
The AD7625 conversion result is available for reading after tMSB
(time from the conversion start until MSB is available) has
elapsed. The user must apply a burst LVDS CLK± signal to the
AD7625 to transfer data to the digital host.
The AD7625 is a 6 MSPS ADC that uses SAR based architecture
incorporating a charge redistribution DAC. Figure 18 shows a
simplified schematic of the ADC. The capacitive DAC consists
of two identical arrays of 16 binary weighted capacitors that are
connected to the two comparator inputs.
The CLK± signal outputs the ADC conversion result onto the
data output D±. The bursting of the CLK± signal is illustrated
in Figure 29 and Figure 30 and is characterized as follows: The
differential voltage on CLK± should be held to create logic low
in the time between tCLKL and tMSB.
During the acquisition phase, the terminals of the array tied
to the input of the comparator are connected to GND via SW+
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 logic high. Note
that the AD7625 can receive a CMOS (CNV+) or LVDS format
(CNV±) signal.
The AD7625 has two data read modes. For more information
about the echoed-clock and self-clocked interface modes, see
the Digital Interface section.
The AD7625 is housed in a space-saving, 32-lead, 5 mm ×
5 mm LFCSP.
Rev. A | Page 13 of 24
AD7625
Data Sheet
TRANSFER FUNCTIONS
ANALOG INPUTS
The AD7625 uses a 4.096 V reference. The AD7625 converts
the differential voltage of the antiphase analog inputs (IN+ and
IN−) into a digital output. The analog inputs, IN+ and IN−,
require a 2.048 V common-mode voltage (REF/2).
The analog inputs, IN+ and IN−, applied to the AD7625 must be
180° out of phase with each other. Figure 20 shows an equivalent
circuit of the input structure of the AD7625.
The 16-bit conversion result is in MSB first, twos complement
format.
011 ... 111
011 ... 110
011 ... 101
VDD1
CNV
ANALOG INPUT
Figure 20. Equivalent Analog Input Circuit
Figure 19. ADC Ideal Transfer Functions (FSR = Full-Scale Range)
Table 7. Output Codes and Ideal Input Voltages
Description
FSR − 1 LSB
Midscale + 1 LSB
Midscale
Midscale − 1 LSB
−FSR + 1 LSB
−FSR
Analog Input
(IN+ − IN−)
REF = 4.096 V
+4.0959375 V
+62.5 μV
0V
−62.5 μV
−4.0959375 V
−4.096 V
Digital Output Code
Twos Complement (Hex)
0x1FFF
0x0001
0x0000
0xFFFF
0x1001
0x1000
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. The
AD7625 shows some degradation in THD with higher analog
input frequencies.
85
80
75
70
65
60
55
50
45
40
1
10
100
1k
10k
100k
1M
INPUT COMMON-MODE FREQUENCY (Hz)
Figure 21. Analog Input CMRR vs. Frequency
Rev. A | Page 14 of 24
10M
07652-009
+FSR – 1LSB
+FSR – 1.5LSB
07652-032
–FSR + 1LSB
–FSR + 0.5LSB
CMRR (dB)
100 ... 001
100 ... 000
–FSR
250Ω 25pF
IN+
OR
IN–
100 ... 010
07652-031
ADC CODE (TWOS COMPLEMENT)
The ideal transfer functions for the AD7625 are shown in
Figure 19 and Table 7.
The two diodes provide ESD protection for the analog inputs,
IN+ and IN−. Care must be taken to ensure that the analog input
signal does not exceed the reference voltage by more than 0.3 V.
If the analog input signal exceeds this level, the diodes become
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
the ADA4899-1 in Figure 24) are different from those of the
reference, the analog input signal may eventually exceed the
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.
Data Sheet
AD7625
TYPICAL CONNECTION DIAGRAM
V+
ADR434 8
ADR444
CAPACITOR ON OUTPUT
FOR STABILITY
CREF
10µF1, 2
VDD1
(5V)
10µF1
10nF
1
VDD1
2
VDD2
ADR280 8
10µF
VIO
10kΩ 3
3
CAP1
4
REFIN
32
31
30
29
28
27
26
25
GND
REF
REF
CAP2
GND
CAP2
CAP2
100nF
REF
100nF
VDD2
(2.5V)
5
EN1
7
VDD2
IN+
IN– 22
IN–
SEE THE DRIVING
THE AD7625 SECTION7
VCM
VCM 21
AD7625
EN0
6
IN+ 23
PADDLE
10kΩ
CONTROL FOR
ENABLE
PINS
GND 24
VDD1 20
100nF
FERRITE
BEAD6
VDD1
(5V)
VDD1 19
VDD2
(2.5V)
D–
D+
VIO
GND
DCO–
DCO+
9
10
11
12
13
14
15
CLK+
CNV+
8
CLK–
CNV–
CONVERSION4
CONTROL
CMOS (CNV+ ONLY)
OR
LVDS CNV+ AND CNV–
USING 100Ω
TERMINATION RESISTOR
VDD2
(2.5V)
VDD2 18
100nF
16
17
100nF
5
100Ω
100Ω
VIO
(2.5V)
100Ω
100Ω
DIGITAL INTERFACE SIGNALS
DIGITAL HOST
LVDS TRANSMIT AND RECEIVE
4
5
6
7
8
FIXED IN HARDWARE OR CONTROLLED USING A DIGITAL HOST (EN0 = 0 AND EN1 = 0 IS AN ILLEGAL STATE).
OPTION TO USE A CMOS (CNV+) OR LVDS (CNV±) INPUT TO CONTROL CONVERSIONS.
TO ENABLE SELF-CLOCKED MODE, TIE DCO+ TO GND USING A PULL-DOWN RESISTOR.
CONNECT PIN 19 AND PIN 20 TO VDD1 SUPPLY; ISOLATE FROM PIN 1 USING A FERRITE BEAD SIMILAR TO WURTH 74279266.
SEE THE DRIVING THE AD7625 SECTION FOR DETAILS ON AMPLIFIER CONFIGURATIONS.
SEE THE VOLTAGE REFERENCE OPTIONS SECTION FOR DETAILS.
Figure 22. Typical Application Diagram
Rev. A | Page 15 of 24
07652-027
1 SEE THE LAYOUT, DECOUPLING, AND GROUNDING SECTION.
2C
REF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESR AND ESL.
3 USE PULL-UP OR PULL-DOWN RESISTORS TO CONTROL EN0, EN1 DURING POWER-UP. EN0 AND EN1 INPUTS CAN BE
AD7625
Data Sheet
DRIVING THE AD7625
ADA4899-1
Differential Analog Input Source
U1
ANALOG INPUT
(UNIPOLAR 0V TO 4.096V)
Figure 24 shows an ADA4899-1 driving each differential input
to the AD7625.
Single-Ended-to-Differential Driver
590Ω
For applications using unipolar analog signals, a single-endedto-differential driver, as shown in Figure 23, allows for a differential input into the part. This configuration, when provided
with an input signal of 0 V to 4.096 V, produces a differential
±4.096 V with midscale at 2.048 V. The one-pole filter using
R = 33 Ω and C = 56 pF provides a corner frequency of 86 MHz.
The VCM output of the AD7625 can be buffered and then used
to provide the required 2.048 V common-mode voltage.
33Ω
56pF
IN+
590Ω
AD7625
IN–
33Ω
U2
VCM
56pF
ADA4899-1
100nF
100nF
V+
V–
AD8031, AD8032
Figure 23. Single-Ended-to-Differential Driver Circuit
REF1
CREF
10µF2
CREF
10µF2
REF1
+VS
33Ω
0V TO VREF
REF
56pF
REFIN
IN+
ADA4899-1 –V
S
AD7625
+VS
IN–
33Ω
VREF TO 0V
ADA4899-1
GND
56pF
VCM
2.048V
–VS
+VS
VCM
BUFFERED VCM PIN OUTPUT
GIVES THE REQUIRED 2.048V
COMMON-MODE SUPPLY FOR
ANALOG INPUTS.
0.1µF
–VS
AD8031, AD8032
THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS
IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.
REF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.
THE REF AND REFIN PINS ARE DECOUPLED REGARDLESS OF EN1 AND EN0 SETTINGS.
2C
Figure 24. Driving the AD7625 from a Differential Analog Source
Rev. A | Page 16 of 24
07652-025
1SEE
07652-033
50Ω
Data Sheet
AD7625
VOLTAGE REFERENCE OPTIONS
Table 8. Voltage Reference Options 1
The AD7625 allows flexible options for creating and buffering
the reference voltage. The AD7625 conversions refer to 4.096 V
only. The various options creating this 4.096 V reference are
controlled by the EN1 and EN0 pins (see Table 8).
Option
A
EN1
1
EN0
1
B
0
1
C
1
0
1
A
V+
V+
EN1 = 0 and EN0 = 0 is an illegal state.
SETTING EN1 = 1 AND EN0 = 1 ENABLES THE INTERNAL
REFERENCE AND REFERENCE BUFFER. DECOUPLE
THE REF AND REFIN PINS EXTERNALLY.
ADR280
ADR434
ADR444
Reference Mode
Use internal reference and internal
reference buffer (both are enabled).
Use external 1.2 V reference with
internal reference buffer enabled.
The internal reference is disabled.
Use external 4.096 V reference with
an external reference buffer. The
internal reference and reference
buffer are disabled.
V+
10µF
10µF
V–
C
B
IN+
REF
REFIN
AD7625
SETTING EN1 = 0 AND EN0 = 1
DISABLES THE INTERNAL REFERENCE
AND ENABLES THE INTERNAL REFERENCE BUFFER.
CONNECT A 1.2V REFERENCE TO THE REFIN PIN. THE 1.2V
APPLIED TO THE REFIN PIN IS BUFFERED INTERNALLY
TO CREATE A 4.096V REFERENCE FOR THE ADC.
IN–
Figure 25. Voltage Reference Options
Rev. A | Page 17 of 24
07652-026
SETTING EN1 = 1 AND EN0 = 0
DISABLES THE INTERNAL REFERENCE
AND REFERENCE BUFFER. CONNECT THE
BUFFERED 4.096V SIGNAL TO
THE REF PIN.
AD7625
Data Sheet
The AD7625 uses both 5 V (VDD1) and 2.5 V (VDD2) power
supplies, as well as a digital input/output interface supply (VIO).
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
best practice to isolate the VIO and VDD2 pins using separate
traces and also to decouple each pin separately.
The 5 V and 2.5 V supplies required for the AD7625 can be
generated using Analog Devices, Inc., low dropout regulators
(LDOs) such as the ADP3330-2.5, ADP3330-5, ADP3334, and
ADP1708.
90
After VIO is established, apply the 2.5 V VDD2 supply to the
device followed by the 5 V VDD1 supply and then an external
reference (depending on the reference setting being used).
Finally, apply the analog inputs to the ADC.
25
VDD2 INTERNAL REF
20
CURRENT (mA)
POWER SUPPLY
VDD2 EXTERNAL REF
15
VIO
10
VDD1 INTERNAL REF
VDD2
85
5
VDD1
0
PSRR (dB)
75
0
1000
2000
3000
4000
5000
6000
7000
SAMPLING RATE (kSPS)
70
07652-016
VDD1 EXTERNAL REF
80
Figure 27. Current Consumption vs. Sampling Rate
65
60
150
140
55
10
100
1k
SUPPLY FREQUENCY (Hz)
10k
Figure 26. PSRR vs. Supply Frequency
(350 mV pp Ripple on VDD2, 600 mV Ripple on VDD1)
Power-Up
When powering up the AD7625 device, first apply the VIO
voltage to the device so that the EN1 and EN0 values can be set
for the reference option in use. Connect the EN0 and EN1 pins
to pull-up/pull-down resistors to ensure that one or both of
these pins is set to a nonzero value. EN0 = 0 and EN1 = 0 is an
illegal state that must be avoided.
Rev. A | Page 18 of 24
130
INTERNAL REF
120
110
100
EXTERNAL REF
90
80
70
60
0
1000
2000
3000
4000
5000
6000
SAMPLING RATE (kSPS)
Figure 28. Power Dissipation vs. Sampling Rate
7000
07652-017
1
POWER DISSIPATION (mW)
50
07652-011
INTERNAL REFERENCE USED
Data Sheet
AD7625
DIGITAL INTERFACE
Conversion Control
The clock DCO± is a buffered copy of CLK± and is synchronous
to the data, D±, which is updated on the falling edge of DCO+
(tD). By maintaining good propagation delay matching between
D± and DCO± through the board and the digital host, DCO±
can be used to latch D± with good timing margin for the shift
register.
All analog-to-digital conversions are controlled by the CNV
signal. This signal can be applied in the form of a CNV+/CNV−
LVDS signal, or it can be applied in the form of a 2.5 V CMOS
logic signal to the CNV+ pin. The conversion is initiated by the
rising edge of the CNV signal.
Conversions are initiated by a CNV± pulse. The CNV± pulse
must be returned low (≤tCNVH maximum) for valid operation.
After a conversion begins, it continues until completion. Additional CNV± pulses are ignored during the conversion phase.
After the time tMSB elapses, the host should begin to burst the
CLK±. Note that tMSB is the maximum time for the MSB of the
new conversion result and should be used as the gating device
for CLK±. The echoed clock, DCO±, and the data, D±, are
driven in phase, with D± being updated on the falling edge of
DCO+; the host should use the rising edge of DCO+ to capture
D±. The only requirement is that the 16 CLK pulses finish
before the time tCLKL elapses for the next conversion phase or the
data is lost. From the time tCLKL to tMSB, D± and DCO± are
driven to 0s. Set CLK± to idle low between CLK± bursts.
After the AD7625 is powered up, the first conversion result
generated is invalid. Subsequent conversion results are valid
provided that the time between conversions does not exceed
the maximum specification for tCYC.
The two methods for acquiring the digital data output of the
AD7625 via the LVDS interface are described in the following
sections.
Echoed-Clock Interface Mode
The digital operation of the AD7625 in echoed-clock interface
mode is shown in Figure 29. This interface mode, requiring
only a shift register on the digital host, can be used with many
digital hosts (FPGA, shift register, microprocessor, and so on).
It requires three LVDS pairs (D±, CLK±, and DCO±) between
each AD7625 and the digital host.
SAMPLE N
SAMPLE N + 1
tCYC
tCNVH
CNV–
CNV+
tACQ
ACQUISITION
ACQUISITION
ACQUISITION
tCLKL
tCLK
15
CLK–
16
1
15
2
16
1
2
3
CLK+
tDCO
15
DCO–
16
1
2
15
1
16
2
3
DCO+
tMSB
D–
D1
N–1
D0
N–1
tD
0
D15
N
D14
N
D1
N
D0
N
Figure 29. Echoed-Clock Interface Mode Timing Diagram
Rev. A | Page 19 of 24
0
D15
N+1
D14
N+1
D13
N+1
07652-003
tCLKD
D+
AD7625
Data Sheet
Self-Clocked Interface Mode
The digital operation of the AD7625 in self-clocked interface
mode is shown in Figure 30. This interface mode reduces the
number of wires between ADCs and the digital host to two LVDS
pairs per AD7625 (CLK± and D±) or to a single pair if sharing a
common CLK± using multiple AD7625 devices. Self-clocked
interface mode facilitates the design of boards that use multiple
AD7625 devices. The digital host can adapt the interfacing
scheme to account for differing propagation delays between
each AD7625 device and the digital host.
Conversions are initiated by a CNV± pulse. The CNV± pulse
must be returned low (≤tCNVH maximum) for valid operation.
After a conversion begins, it continues until completion. Additional CNV± pulses are ignored during the conversion phase.
After the time tMSB elapses, the host should begin to burst the
CLK±. Note that tMSB is the maximum time for the first bit of
the header and should be used as the gating device for CLK±.
CLK± is also used internally on the host to begin the internal
synchronization state machine. The next header bit and conversion
results are output on subsequent falling edges of CLK±. The
only requirement is that the 18 CLK± pulses finish before the
time tCLKL elapses for the next conversion phase or the data is
lost. Set CLK± to idle high between bursts of 18 CLK± pulses.
The self-clocked interface mode consists of preceding the results
of each ADC word with a 2-bit header on the data, D±. This
header is used to synchronize D± of each conversion in the
digital host. Synchronization is accomplished by one simple
state machine per AD7625 device. For example, if the state
machine is running at the same speed as CLK± with three
phases, the state machine measures when the Logic 1 of the
header occurs.
SAMPLE N
SAMPLE N + 1
tCYC
tCNVH
CNV–
CNV+
tACQ
ACQUISITION
ACQUISITION
ACQUISITION
tCLK
tCLKL
17
CLK–
18
1
3
2
17
4
1
18
2
3
CLK+
D+
D–
D1
N–1
D0
N–1
0
1
0
D15
N
D14
N
D1
N
Figure 30. Self-Clocked Interface Mode Timing Diagram
Rev. A | Page 20 of 24
D0
N
0
1
0
D15
N+1
07652-004
tMSB
tCLKD
Data Sheet
AD7625
APPLICATIONS INFORMATION
LAYOUT, DECOUPLING, AND GROUNDING
When laying out the printed circuit board (PCB) for the AD7625,
follow the practices described in this section to obtain the maximum performance from the converter.
supply to Pin 19 and Pin 20 using a 100 nF capacitor to GND.
This GND connection can be placed a short distance away from
the exposed paddle.
VIO Supply Decoupling
Exposed Paddle
Decouple the VIO supply applied to Pin 12 to ground at Pin 13.
The AD7625 has an exposed paddle on the underside of the
package.
Layout and Decoupling of Pin 25 to Pin 32
•
•
•
•
Solder the paddle directly to the PCB.
Connect the paddle to the ground plane of the board using
multiple vias, as shown in Figure 31.
Decouple all supply pins except for Pin 12 (VIO) directly to
the paddle, minimizing the current return path.
Pin 13 and Pin 24 can be connected directly to the paddle.
Use vias to ground at the point where these pins connect to
the paddle.
VDD1 Supply Routing and Decoupling
The VDD1 supply is connected to Pin 1, Pin 19, and Pin 20. The
supply should be decoupled using a 100 nF capacitor at Pin 1.
The user 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
Connect the outputs of Pin 25, Pin 26, and Pin 28 together and
decouple them to Pin 27 using a 10 μF capacitor with low ESR
and low ESL.
Reduce the inductance of the path connecting Pin 25, Pin 26,
and Pin 28 by widening the PCB traces connecting these pins.
A similar approach should be taken in the connections used for
the reference pins of the AD7625. Connect Pin 29, Pin 30, and
Pin 32 together using widened PCB traces to reduce inductance.
In internal or external reference mode, a 4.096 V reference voltage
is output on Pin 29, Pin 30, and Pin 32. Decouple these pins to
Pin 31 using a 10 μF capacitor with low ESR and low ESL.
Figure 31 shows an example of the recommended layout for
the underside of the AD7625 device. Note the extended signal
trace connections and the outline of the capacitors decoupling
the signals applied to the REF pins (Pin 29, Pin 30, and Pin 32)
and to the CAP2 pins (Pin 25, Pin 26, and Pin 28).
24 23 22 21 20 19 18 17
25
4.096V
EXTERNAL REFERENCE
(ADR434 OR ADR444)
16
Paddle
26
15
27
14
28
13
29
12
30
11
31
10
32
9
2
3
4
5
6
7
8
07652-013
1
Figure 31. PCB Layout and Decoupling Recommendations for Pin 24 to Pin 32
Rev. A | Page 21 of 24
AD7625
Data Sheet
OUTLINE DIMENSIONS
0.30
0.25
0.18
32
25
0.50
BSC
TOP VIEW
0.80
0.75
0.70
8
16
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
SEATING
PLANE
3.25
3.10 SQ
2.95
EXPOSED
PAD
17
0.50
0.40
0.30
PIN 1
INDICATOR
1
24
9
BOTTOM VIEW
0.25 MIN
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-WHHD.
112408-A
PIN 1
INDICATOR
5.10
5.00 SQ
4.90
Figure 32. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
5 mm × 5 mm Body, Very Very Thin Quad
(CP-32-7)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1, 2, 3
AD7625BCPZ
AD7625BCPZ-RL7
EVAL-AD7625EDZ
EVAL-CED1Z
1
2
3
Temperature Range
−40°C to +85°C
−40°C to +85°C
Package Description
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
Evaluation Board
Converter Evaluation and Development Board
Package Option
CP-32-7
CP-32-7
Z = RoHS Compliant Part.
The EVAL-AD7625EDZ board can be used as a standalone evaluation board or in conjunction with the EVAL-CED1Z for evaluation/demonstration purposes.
The EVAL-CED1Z 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 22 of 24
Data Sheet
AD7625
NOTES
Rev. A | Page 23 of 24
AD7625
Data Sheet
NOTES
©2009–2012 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07652-0-7/12(A)
Rev. A | Page 24 of 24