a
AD7671
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Fax: 781/326-8703 © Analog Devices, Inc. All rights reserved.
16-Bit, 1 MSPS CMOS ADC
FUNCTIONAL BLOCK DIAGRAM
DGNDDVDDAVDD AGND REF REFGND
SWITCHED
CAP DAC
CNVSTIMPULSEWARP
OGND
16
CONTROL LOGIC AND
CALIBRATION CIRCUITRY
CLOCK
IND(4R) 4R
OVDD
AD7671
INGND
PD
RESET
BYTESWAP
SER/PAR
D[15:0]
BUSY
CS
RD
OB/2C
SERIAL
PORT
PARALLEL
INTERFACE
INA(R) R
INC(4R) 4R
INB(2R) 2R
FEATURES
Throughput
1 MSPS (Warp Mode)
800 kSPS (Normal Mode)
INL: 2.5 LSB Max (0.0038% of Full Scale)
16-Bit Resolution with No Missing Codes
S/(N+D): 90 dB Typ @ 250 kHz
THD: –100 dB Typ @ 250 kHz
Analog Input Voltage Ranges
Bipolar: 10 V, 5 V, 2.5 V
Unipolar: 0 V to 10 V, 0 V to 5 V, 0 V to 2.5 V
Both AC and DC Specifications
No Pipeline Delay
Parallel (8/16 Bits) and Serial 5 V/3 V Interface
SPI®/QSPI™/MICROWIRE™/DSP Compatible
Single 5 V Supply Operation
Power Dissipation
112 mW Typical
15 W @ 100 SPS
Power-Down Mode: 7 W Max
Package: 48-Lead Quad Flatpack (LQFP)
Package: 48-Lead Chip Scale (LFCSP)
Pin-to-Pin Compatible Upgrade of the AD7665/AD7664
APPLICATIONS
Data Acquisition
Communication
Instrumentation
Spectrum Analysis
Medical Instruments
Process Control
GENERAL DESCRIPTION
The AD7671 is a 16-bit, 1 MSPS, charge redistribution SAR,
analog-to-digital converter that operates from a single 5 V power
supply. It contains a high speed 16-bit sampling ADC, a resistor
input scaler that allows various input ranges, an internal
conversion clock, error correction circuits, and both serial
and parallel system interface ports.
The AD7671 is hardware factory-calibrated and is comprehen-
sively tested to ensure such ac parameters as signal-to-noise ratio
(SNR) and total harmonic distortion (THD), in addition to the
more traditional dc parameters of gain, offset, and linearity.
It features a very high sampling rate mode (Warp), a fast mode
(Normal) for asynchronous conversion rate applications,
and, for
low power applications, a reduced power mode (Impulse)
where
the power is scaled with the throughput.
It is fabricated using Analog Devices’ high performance, 0.6 micron
CMOS process and is available in a 48-lead LQFP and a tiny
48-lead LFCSP, with operation specified from –40∞C to +85∞C.
PRODUCT HIGHLIGHTS
1. Fast Throughput
The AD7671 is a very high speed (1 MSPS in Warp Mode
and 800 kSPS in Normal Mode), charge redistribution, 16-bit
SAR ADC.
2. Single-Supply Operation
The AD7671 operates from a single 5 V supply, dissipates
only 112 mW typical, even lower when a reduced throughput
is used with the reduced power mode (Impulse) and a power-
down mode.
3. Superior INL
The AD7671 has a maximum integral nonlinearity of 2.5 LSB
with no missing 16-bit code.
4. Serial or Parallel Interface
Versatile parallel (8 bits or 16 bits) or 2-wire serial interface
arrangement compatible with both 3 V or 5 V logic.
PulSAR Selection
Type/kSPS 100–250 500–570 800–1000
Pseudo AD7660 AD7650
Differential AD7664
True Bipolar AD7663 AD7665 AD7671
True Differential AD7675 AD7676 AD7677
18-Bit AD7678 AD7679 AD7674
Simultaneous/ AD7654 AD7655
Multichannel
REV. C
2012
___
–2–
AD7671–SPECIFICATIONS
(–40C to +85C, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise noted.)
Parameter Conditions Min Typ Max Unit
RESOLUTION 16 Bits
ANALOG INPUT
Voltage Range V
IND
– V
INGND
±4 REF, 0 V to 4 REF, ±2 REF (See Table I)
Common-Mode Input Voltage V
INGND
–0.1 +0.5 V
Analog Input CMRR f
IN
= 100 kHz 74 dB
Input Impedance See Table I
THROUGHPUT SPEED
Complete Cycle In Warp Mode 1 ms
Throughput Rate In Warp Mode 1 1000 kSPS
Time between Conversions In Warp Mode 1 ms
Complete Cycle In Normal Mode 1.25 ms
Throughput Rate In Normal Mode 0 800 kSPS
Complete Cycle In Impulse Mode 1.5 ms
Throughput Rate In Impulse Mode 0 666 kSPS
DC ACCURACY
Integral Linearity Error –2.5 +2.5 LSB
1
No Missing Codes 16 Bits
Transition Noise 0.7 LSB
Bipolar Zero Error
2
, T
MIN
to T
MAX
±5 V Range, Normal or –45 +45 LSB
Impulse Modes
Other Range or Mode –0.1 +0.1 % of FSR
Bipolar Full-Scale Error
2
, T
MIN
to T
MAX
–0.38 +0.38 % of FSR
Unipolar Zero Error
2
, T
MIN
to T
MAX
–0.18 +0.18 % of FSR
Unipolar Full-Scale Error
2
, T
MIN
to T
MAX
–0.76 +0.76 % of FSR
Power Supply Sensitivity AVDD = 5 V ±5% ±9.5 LSB
AC ACCURACY
Signal-to-Noise f
IN
= 20 kHz 89 90 dB
3
f
IN
= 250 kHz 90 dB
Spurious-Free Dynamic Range f
IN
= 250 kHz 100 dB
Total Harmonic Distortion f
IN
= 20 kHz –100 –96 dB
f
IN
= 250 kHz –100 dB
Signal-to-(Noise+Distortion) f
IN
= 20 kHz 88.5 90 dB
f
IN
= 250 kHz, –60 dB Input 30 dB
–3 dB Input Bandwidth 9.6 MHz
SAMPLING DYNAMICS
Aperture Delay 2ns
Aperture Jitter 5ps rms
Transient Response Full-Scale Step 250 ns
REFERENCE
External Reference Voltage Range 2.3 2.5 AVDD – 1.85 V
External Reference Current Drain 1 MSPS Throughput 200 mA
DIGITAL INPUTS
Logic Levels
V
IL
–0.3 +0.8 V
V
IH
+2.0 DVDD + 0.3 V
I
IL
–1+1mA
I
IH
–1+1mA
DIGITAL OUTPUTS
Data Format Parallel or Serial 16-Bit
Pipeline Delay Conversion Results Available Immediately
after Completed Conversion
V
OL
I
SINK
= 1.6 mA 0.4 V
V
OH
I
SOURCE
= –570 mAOVDD – 0.6 V
REV. C
–3–
AD7671
Parameter Conditions Min Typ Max Unit
POWER SUPPLIES
Specified Performance
AVDD 4.75 5 5.25 V
DVDD 4.75 5 5.25 V
OVDD 2.7 5.25
4
V
Operating Current
5
1 MSPS Throughput
AVDD 15 mA
DVDD
6
7.2 mA
OVDD
6
37 mA
Power Dissipation
6, 7
666 kSPS Throughput
8
84 95 mW
100 SPS Throughput
8
15 mW
1 MSPS Throughput
5
112 125 mW
In Power-Down Mode
9
7mW
TEMPERATURE RANGE
10
Specified Performance T
MIN
to T
MAX
–40 +85 ∞C
NOTES
1
LSB means least significant bit. With the ±5 V input range, one LSB is 152.588 mV.
2
See Definition of Specifications section. These specifications do not include the error contribution from the external reference.
3
All specifications in dB are referred to a full-scale input FS. Tested with an input signal at 0.5 dB below full scale, unless otherwise specified.
4
The max should be the minimum of 5.25 V and DVDD + 0.3 V.
5
In Warp Mode.
6
Tested in Parallel Reading Mode.
7
Tested with the 0 V to 5 V range and V
IN
– V
INGND
= 0 V. See Power Dissipation section.
8
In Impulse Mode.
9
With OVDD below DVDD + 0.3 V and all digital inputs forced to DVDD or DGND, respectively.
10
Contact factory for extended temperature range.
Specifications subject to change without notice.
Table I. Analog Input Configuration
Input Voltage Input
Range IND(4R) INC(4R) INB(2R) INA(R) Impedance
1
±4 REF
2
V
IN
INGND INGND REF 1.63 kW
±2 REF V
IN
V
IN
INGND REF 948 W
±REF V
IN
V
IN
V
IN
REF 711 W
0 V to 4 REF V
IN
V
IN
INGND INGND 948 W
0 V to 2 REF V
IN
V
IN
V
IN
INGND 711 W
0 V to REF V
IN
V
IN
V
IN
V
IN
Note 3
NOTES
1
Typical analog input impedance.
2
With REF = 3 V, in this range, the input should be limited to –11 V to +12 V.
3
For this range the input is high impedance.
TIMING SPECIFICATIONS
Parameter
Symbol Min Typ Max Unit
Refer to Figures 11 and 12
Convert Pulsewidth t
1
5ns
Time between Conversions t
2
1/1.25/1.5 Note 1 ms
(Warp Mode/Normal Mode/Impulse Mode)
CNVST LOW to BUSY HIGH Delay t
3
30 ns
BUSY HIGH All Modes Except in Master Serial Read after t
4
0.75/1/1.25 ms
Convert Mode (Warp Mode/Normal Mode/Impulse Mode)
Aperture Delay t
5
2ns
End of Conversion to BUSY LOW Delay t
6
10 ns
Conversion Time (Warp Mode/Normal Mode/Impulse Mode) t
7
0.75/1/1.25 ms
Acquisition Time t
8
250 ns
RESET Pulsewidth t
9
10 ns
(–40C to +85C, AVDD = DVDD = 5 V, OVDD = 2.7 V to 5.25 V, unless otherwise noted.)
REV. C
AD7671
–4–
TIMING SPECIFICATIONS
(continued)
Parameter
Symbol Min Typ Max Unit
Refer to Figures 13, 14, 15, and 16 (Parallel Interface Modes)
CNVST LOW to DATA Valid Delay t
10
0.75/1/1.25 ms
(Warp Mode/Normal Mode/Impulse Mode)
DATA Valid to BUSY LOW Delay t
11
20 ns
Bus Access Request to DATA Valid t
12
40 ns
Bus Relinquish Time t
13
515ns
Refer to Figures 17 and 18 (Master Serial Interface Modes)
2
CS LOW to SYNC Valid Delay t
14
10 ns
CS LOW to Internal SCLK Valid Delay t
15
10 ns
CS LOW to SDOUT Delay t
16
10 ns
CNVST LOW to SYNC Delay (Read during Convert) t
17
25/275/525 ns
(Warp Mode/Normal Mode/Impulse Mode)
SYNC Asserted to SCLK First Edge Delay
3
t
18
4ns
Internal SCLK Period
3
t
19
25 40 ns
Internal SCLK HIGH
3
t
20
15 ns
Internal SCLK LOW
3
t
21
9.5 ns
SDOUT Valid Setup Time
3
t
22
4.5 ns
SDOUT Valid Hold Time
3
t
23
2ns
SCLK Last Edge to SYNC Delay
3
t
24
3
CS HIGH to SYNC HI-Z t
25
10 ns
CS HIGH to Internal SCLK HI-Z t
26
10 ns
CS HIGH to SDOUT HI-Z t
27
10 ns
BUSY HIGH in Master Serial Read after Convert
3
t
28
See Table II ms
CNVST LOW to SYNC Asserted Delay t
29
0.75/1/1.25 ms
(Warp Mode/Normal Mode/Impulse Mode)
Master Serial Read after Convert
SYNC Deasserted to BUSY LOW Delay t
30
25 ns
Refer to Figures 19 and 21 (Slave Serial Interface Modes)
External SCLK Setup Time t
31
5ns
External SCLK Active Edge to SDOUT Delay t
32
316ns
SDIN Setup Time t
33
5ns
SDIN Hold Time t
34
5ns
External SCLK Period t
35
25 ns
External SCLK HIGH t
36
10 ns
External SCLK LOW t
37
10 ns
NOTES
1
In Warp Mode only, the maximum time between conversions is 1 ms; otherwise, there is no required maximum time.
2
In serial interface modes, the SYNC, SCLK, and SDOUT timings are defined with a maximum load C
L
of 10 pF; otherwise, the load is 60 pF maximum.
3
In Serial Master Read during Convert Mode. See Table II for Master Read after Convert Mode.
Specifications subject to change without notice.
Table II. Serial Clock Timings in Master Read after Convert
DIVSCLK[1] 0011
DIVSCLK[0] 0101 Unit
SYNC to SCLK First Edge Delay Minimum t
18
4202020 ns
Internal SCLK Period Minimum t
19
25 50 100 200 ns
Internal SCLK Period Maximum t
19
40 70 140 280 ns
Internal SCLK HIGH Minimum t
20
15 25 50 100 ns
Internal SCLK LOW Minimum t
21
9244999 ns
SDOUT Valid Setup Time Minimum t
22
4.5 22 22 22 ns
SDOUT Valid Hold Time Minimum t
23
243089 ns
SCLK Last Edge to SYNC Delay Minimum t
24
360140 300 ns
BUSY HIGH Width Maximum (Warp) t
28
1.5 2 3 5.25 ms
BUSY HIGH Width Maximum (Normal) t
28
1.75 2.25 3.25 5.5 ms
BUSY HIGH Width Maximum (Impulse) t
28
22.5 3.5 5.75 ms
Specifications subject to change without notice.
REV. C
AD7671
–5–
PIN CONFIGURATION
ST-48 and CP-48
36
35
34
33
32
31
30
29
28
27
26
25
13 14 15 16 17 18 19 20 21 22 23 24
1
2
3
4
5
6
7
8
9
10
11
12
48 47 46 45 44 39 38 3743 42 41 40
PIN 1
IDENTIFIER
TOP VIEW
(Not to Scale)
AGND
CNVST
PD
RESET
CS
RD
DGND
AGND
AVDD
NC
BYTESWAP
OB/2C
WARP
IMPULSE
NC = NO CONNECT
SER/PAR
D0
D1
D2/DIVSCLK[0]
BUSY
D15
D14
D13
AD7671
D3/DIVSCLK[1] D12
D4/EXT/INT
D5/INVSYNC
D6/INVSCLK
D7/RDC/SDIN
OGND
OVDD
DVDD
DGND
D8/SDOUT
D9/SCLK
D10/SYNC
D11/RDERROR
NC
NC
NC
NC
NC
IND(4R)
INC(4R)
INB(2R)
INA(R)
INGND
REFGND
REF
ABSOLUTE MAXIMUM RATINGS
1
Analog Inputs
IND
2
, INC
2
, INB
2
. . . . . . . . . . . . . . . . . . . . –11 V to +30 V
INA, REF, INGND, REFGND, AGND
. . . . . . . . . . . . . . . . . . . . . . . . . . . – 0.3 V to AVDD + 0.3 V
Ground Voltage Differences
AGND, DGND, OGND . . . . . . . . . . . . . . . . . . . . . . ±0.3 V
Supply Voltages
AVDD, DVDD, OVDD . . . . . . . . . . . . . . . . . –0.3 V to +7 V
AVDD to DVDD,
AVDD to OVDD . . . . . . . . . . . . . . ±7 V
DVDD to OVDD . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
Digital Inputs . . . . . . . . . . . . . . . . –0.3 V to DVDD + 0.3 V
Internal Power Dissipation
3
. . . . . . . . . . . . . . . . . . . . 700 mW
Internal Power Dissipation
4
. . . . . . . . . . . . . . . . . . . . . . 2.5 W
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150∞C
Storage Temperature Range . . . . . . . . . . . . –65∞C to +150∞C
Lead Temperature Range
(Soldering 10 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 300∞C
NOTES
1
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.
2
See Analog Inputs section.
3
Specification is for device in free air: 48-Lead LQFP: q
JA
= 91∞C/W, q
JC
= 30∞C/W.
4
Specification is for device in free air: 48-Lead LFCSP: q
JA
= 26∞C/W.
IOH
500A
1.6mA IOL
TO OUTPUT
PIN 1.4V
*IN SERIAL INTERFACE MODES, THE SYNC, SCLK, AND
SDOUT TIMINGS ARE DEFINED WITH A MAXIMUM LOAD
CL OF 10pF; OTHERWISE, THE LOAD IS 60pF MAXIMUM.
CL
60pF*
Figure 1. Load Circuit for Digital Interface Timing,
SDOUT, SYNC, SCLK Outputs, C
L
= 10 pF
tDELAY tDELAY
0.8V
0.8V 0.8V
2V2V
2V
Figure 2. Voltage Reference Levels for Timing
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD7671 features proprietary ESD protection circuitry, permanent damage may occur on
devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are
recommended to avoid performance degradation or loss of functionality.
REV. C
NOTES:
1. PADDLE CONNECTED TO AGND FOR THE LFCSP (CP-48-1). THIS
CONNECTION IS NOT REQUIRED TO MEET THE ELECTRICAL
PERFORMANCES.
-1
AD7671
–6–
PIN FUNCTION DESCRIPTION
Pin
No. Mnemonic Type Description
1AGND P Analog Power Ground Pin.
2AVDD P Input Analog Power Pin. Nominally 5 V.
3, 44–48 NC No Connect.
4BYTESWAP Parallel Mode Selection (8-/16-Bit). When LOW, the LSB is output on D[7:0] and the MSB is
output on D[15:8]. When HIGH, the LSB is output on D[15:8] and the MSB is output on D[7:0].
5OB/2C DI Straight Binary/Binary Twos Complement. When OB/2C is HIGH, the digital output is straight
binary; when LOW, the MSB is inverted, resulting in a twos complement output from its internal
shift register.
6WARP DI Mode Selection. When HIGH and IMPULSE LOW, this input selects the fastest mode, the maximum
throughput is achievable and a minimum conversion rate must be applied in order to guarantee
full specified accuracy. When LOW, full accuracy is maintained independent of the minimum
conversion rate.
7IMPULSE DI Mode Selection. When HIGH and WARP LOW, this input selects a reduced Power Mode.
In this mode, the power dissipation is approximately proportional to the sampling rate.
8SER/PAR DI Serial/Parallel Selection Input. When LOW, the Parallel Port is selected; when HIGH, the Serial
Interface Mode is selected and some bits of the data bus are used as a Serial Port.
9, 10 D[0:1] DO Bit 0 and Bit 1 of the Parallel Port Data Output Bus. When SER/PAR is HIGH, these outputs are
in high impedance.
11, 12 D[2:3] or DI/O When SER/PAR is LOW, these outputs are used as Bit 2 and Bit 3 of the Parallel Port Data
Output Bus.
DIVSCLK[0:1] When SER/PAR is HIGH, EXT/INT is LOW and RDC/SDIN is LOW, which is the Serial Master
Read after Convert Mode. These inputs, part of the Serial Port, are used to slow down, if desired,
the internal serial clock that clocks the data output. In the other serial modes, these pins are high
impedance outputs.
13 D[4] DI/O When SER/PAR is LOW, this output is used as Bit 4 of the Parallel Port Data Output Bus.
or EXT/INT When SER/PAR is HIGH, this input, part of the Serial Port, is used as a digital select input for
choosing the internal or an external data clock, called Master and Slave Modes, respectively. With
EXT/INT tied LOW, the internal clock is selected on SCLK output. With EXT/INT set to a logic
HIGH, output data is synchronized to an external clock signal connected to the SCLK input and
the external clock is gated by CS.
14 D[5] DI/O When SER/PAR is LOW, this output is used as Bit 5 of the Parallel Port Data Output Bus.
or INVSYNC When SER/PAR is HIGH, this input, part of the Serial Port, is used to select the active state of
the SYNC signal. When LOW, SYNC is active HIGH. When HIGH, SYNC is active LOW.
15 D[6] DI/O When SER/PAR is LOW, this output is used as Bit 6 of the Parallel Port Data Output Bus.
or INVSCLK When SER/PAR is HIGH, this input, part of the Serial Port, is used to invert the SCLK signal. It is
active in both Master and Slave Mode.
16 D[7] DI/O When SER/PAR is LOW, this output is used as Bit 7 of the Parallel Port Data Output Bus.
or RDC/SDIN When SER/PAR is HIGH, this input, part of the Serial Port, is used as either an external data input
or a read mode selection input, depending on the state of EXT/INT.
When EXT/INT is HIGH, RDC/SDIN could be used as a data input to daisy-chain the conversion
results from two or more ADCs onto a single SDOUT line. The digital data level on SDIN is output
on DATA with a delay of 16 SCLK periods after the initiation of the read sequence.
When EXT/INT is LOW, RDC/SDIN is used to select the Read Mode. When RDC/SDIN is HIGH,
the previous data is output on SDOUT during conversion. When RDC/SDIN is LOW, the data can
be output on SDOUT only when the conversion is complete.
17 OGND P Input/Output Interface Digital Power Ground.
18 OVDD P Input/Output Interface Digital Power. Nominally at the same supply as the supply of the host
interface (5 V or 3 V).
19 DVDD P Digital Power. Nominally at 5 V.
20 DGND P Digital Power Ground.
REV. C
–7–
AD7671
PIN FUNCTION DESCRIPTION (continued)
Pin
No. Mnemonic Type Description
21 D[8] DO When SER/PAR is LOW, this output is used as Bit 8 of the Parallel Port Data Output Bus.
or SDOUT When SER/PAR is HIGH, this output, part of the Serial Port, is used as a serial data output
synchronized to SCLK. Conversion results are stored in an on-chip register. The AD7671 provides
the conversion result, MSB first, from its internal shift register. The data format is determined
by the logic level of OB/2C. In Serial Mode, when EXT/INT is LOW, SDOUT is valid on both
edges of SCLK.
In Serial Mode, when EXT/INT is HIGH:
If INVSCLK is LOW, SDOUT is updated on SCLK rising edge and valid on the next falling edge.
If INVSCLK is HIGH, SDOUT is updated on SCLK falling edge and valid on the next rising edge.
22 D[9] DI/O When SER/PAR is LOW, this output is used as Bit 9 of the Parallel Port Data Output Bus.
or SCLK When SER/PAR is HIGH, this pin, part of the Serial Port, is used as a serial data clock input or
output, dependent upon the logic state of the EXT/INT pin. The active edge where the data SDOUT
is updated depends upon the logic state of the INVSCLK pin.
23 D[10] DO When SER/PAR is LOW, this output is used as Bit 10 of the Parallel Port Data Output Bus.
or SYNC When SER/PAR is HIGH, this output, part of the Serial Port, is used as a digital output frame
synchronization for use with the internal data clock (EXT/INT = Logic LOW). When a read sequence
is initiated and INVSYNC is LOW, SYNC is driven HIGH and remains HIGH while SDOUT
output is valid. When a read sequence is initiated and INVSYNC is HIGH, SYNC is driven LOW
and remains LOW while SDOUT output is valid.
24 D[11] DO When SER/PAR is LOW, this output is used as Bit 11 of the Parallel Port Data Output Bus.
or RDERROR When SER/PAR is HIGH and EXT/INT is HIGH, this output, part of the Serial Port, is used as an
incomplete read error flag. In Slave Mode, when a data read is started and not complete when the
following conversion is complete, the current data is lost and RDERROR is pulsed HIGH.
25–28 D[12:15] DO Bit 12 to Bit 15 of the Parallel Port Data Output Bus. When SER/PAR is HIGH, these outputs are in
high impedance.
29 BUSY DO Busy Output. Transitions HIGH when a conversion is started and remains HIGH until the conversion
is complete and the data is latched into the on-chip shift register. The falling edge of BUSY could
be used as a data-ready clock signal.
30 DGND P Must Be Tied to Digital Ground.
31 RD DI Read Data. When CS and RD are both LOW, the Interface Parallel or Serial Output Bus is enabled.
32 CS DI Chip Select. When CS and RD are both LOW, the Interface Parallel or Serial Output Bus is enabled.
CS is also used to gate the external serial clock.
33 RESET DI Reset Input. When set to a logic HIGH, reset the AD7671. Current conversion, if any, is aborted.
If not used, this pin could be tied to DGND.
34 PD DI Power-Down Input. When set to a logic HIGH, power consumption is reduced and conversions are
inhibited after the current one is completed.
35 CNVST DI Start Conversion. A falling edge on CNVST puts the internal sample-and-hold into the hold state
and initiates a conversion. In Impulse Mode (IMPULSE HIGH and WARP LOW), if CNVST is
held LOW when the acquisition phase (t
8
) is complete, the internal sample-and-hold is put into the
hold state and a conversion is immediately started.
36 AGND P Must Be Tied to Analog Ground.
37 REF AI Reference Input Voltage.
38 REFGND AI Reference Input Analog Ground.
39 INGND P Analog Input Ground.
40, 41, INA, INB, AI Analog Inputs. Refer to Table I for input range configuration.
42, 43 INC, IND
NOTES
AI = Analog Input
DI = Digital Input
DI/O = Bidirectional Digital
DO = Digital Output
P = Power
REV. C
Paddle connected to AGND for the LFCSP (CP-48-1). This connection is not required to meet the electrical performances.
AD7671
–8–
DEFINITION OF SPECIFICATIONS
Integral Nonlinearity Error (INL)
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 1/2 LSB
before the first code transition. Positive full scale is defined as a
level 1 1/2 LSB beyond the last code transition. The deviation is
measured from the middle of each code to the true straight line.
Differential Nonlinearity Error (DNL)
In an ideal ADC, code transitions are 1 LSB apart. Differential
nonlinearity is the maximum deviation from this ideal value. It is
often specified in terms of resolution for which no missing codes
are guaranteed.
Full-Scale Error
The last transition (from 011 ...10 to 011 . . . 11 in twos
complement coding) should occur for an analog voltage 1 1/2 LSB
below the nominal full scale (2.499886 V for the ±2.5 V range).
The full-scale error is the deviation of the actual level of the last
transition from the ideal level.
Bipolar Zero Error
The difference between the ideal midscale input voltage (0 V) and
the actual voltage producing the midscale output code.
Unipolar Zero Error
In Unipolar Mode, the first transition should occur at a level
1/2 LSB above analog ground. The unipolar zero error is the
deviation of the actual transition from that point.
Spurious-Free Dynamic Range (SFDR)
The difference, in decibels (dB), between the rms amplitude of
the input signal and the peak spurious signal.
Effective Number of Bits (ENOB)
A measurement of the resolution with a sine wave input. It is
related to S/(N+D) by the following formula:
ENOB = (S/[N + D]
dB
– 1.76)/6.02)
and is expressed in bits.
Total Harmonic Distortion (THD)
The rms sum of the first five harmonic components to the rms
value of a full-scale input signal, expressed in decibels.
Signal-to-Noise Ratio (SNR)
The ratio of the rms value of the actual input signal to the rms
sum of all other spectral components below the Nyquist fre-
quency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Signal-to-(Noise + Distortion) Ratio (S/[N+D])
The ratio of the rms value of the actual input signal to the rms
sum of all other spectral components below the Nyquist fre-
quency, including harmonics but excluding dc. The value for
S/(N+D) is expressed in decibels.
Aperture Delay
A measure of the acquisition performance measured from the
falling edge of the CNVST input to when the input signal is
held for a conversion.
Transient Response
The time required for the AD7671 to achieve its rated accuracy
after a full-scale step function is applied to its input.
REV. C
–9–
Typical Performance Characteristics–AD7671
2.5
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–2.5
0 16384 32768 49152 65536
INL – LSB
CODE
TPC 1. Integral Nonlinearity vs. Code
0
DNL – LSB
CODE
16384
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
–0.25
32768 49152 65536
–0.50
–1.00
–0.75
TPC 2. Differential Nonlinearity vs. Code
0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0
NUMBER OF UNITS
POSITIVE INL – LSB
60
50
40
30
20
10
0
TPC 3. Typical Positive INL Distribution (314 Units)
60
50
40
30
20
10
0
–3.0 –2.7 –2.4 –2.1 –1.8 –1.5 –1.2 –0.9 –0.6 –0.3
NUMBER OF UNITS
NEGATIVE INL – LSB
TPC 4. Typical Negative INL Distribution (314 Units)
0
1000
2000
3000
4000
5000
6000
7000
8000
7FFD 7FFE 7FFF 8000 8001 8002 8003 8004 8005 8005
CODE IN HEXA
COUNTS
0017 25
1297
7029 7039
986
00
TPC 5. Histogram of 16,384 Conversions of a DC Input at
the Code Transition
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
7FFC 7FFD 7FFE 7FFF 8000 8001 8002 8003 8004 8005 8006
CODE IN HEXA
COUNTS
002132 100106
3296 3344
9503
TPC 6. Histogram of 16,384 Conversions of a DC Input at
the Code Center
REV. C
AD7671
–10–
0
AMPLITUDE – dB of Full Scale
FREQUENCY – kHz
100 200 300 400 500
0
–20
–40
–60
–80
–100
–120
–140
–160
–180
FS = 1MSPS
fIN = 45.5322kHz
SNR = 89.45dB
THD = –100.05dB
SFDR = 100.49dB
SINAD = 89.1dB
TPC 7. FFT Plot
FREQUENCY – kHz
70
110
SNR AND S/[N+D] – dB
75
85
95
100
1000
SNR
100
90
80
13.0
13.5
14.5
15.5
16.0
15.0
14.0
ENOB – Bits
SINAD
ENOB
TPC 8. SNR, S/(N + D), and ENOB vs. Frequency
92
SNR (REFERRED TO FULL SCALE) – dB
INPUT LEVEL – dB
–80
90
88
86
–70 –60 –50 –40 –30 –20 –10 0
TPC 9. SNR vs. Input Level
96
93
90
87
84
–98
–100
–102
–104
–55 –35 –15 5 25 45 65 85 105 125
SNR – dB
THD – dB
TEMPERATURE – C
THD
SNR
TPC 10. SNR, THD vs. Temperature
THD
SECOND HARMONIC
THIRD HARMONIC
SFDR
–60
–65
–70
–75
–80
–85
–90
–95
–100
–105
–110
–115
110
105
100
95
90
85
80
75
70
65
60
1 10 100 1000
THD, HARMONICS – dB
SFDR – dB
FREQUENCY – kHz
TPC 11. THD, Harmonics, and SFDR vs. Frequency
–60
–70
–80
–90
–100
–110
–120
–130
–140
–150
–60 –50 –40 –30 –20 –10 0
THD, HARMONICS – dB
INPUT LEVEL – dB
THD
THIRD HARMONIC
SECOND HARMONIC
TPC 12. THD, Harmonics vs. Input Level
REV. C
AD7671
–11–
50
40
30
20
10
0
0 50 100 150 200
t12 DELAY – ns
CL – pF
TPC 13. Typical Delay vs. Load Capacitance C
L
OPERATING CURRENTS – A
SAMPLING RATE – SPS
0.001
0.01
0.1
0
10
100
1000
10000
100000
110100 1000 10000 100000 1000000
AVDD, WARP/NORMAL
DVDD, WARP/NORMAL
AV DD, IMPULSE
DVDD, IMPULSE
OVDD, ALL MODES
TPC 14. Operating Currents vs. Sample Rate
1000
900
800
700
600
500
400
300
200
100
0
–55 –35 –15 5 25 45 65 85 105
POWER-DOWN OPERATING CURRENTS – nA
TEMPERATURE – C
DVDD
AVDD
OVDD
TPC 15. Power-Down Operating Currents vs. Temperature
TEMPERATURE – C
10
–10–55 125–35
LSB
–15 5 25 456585105
8
0
–4
–6
–8
6
4
–2
2
OFFSET
–FS
+FS
TPC 16. +FS, Offset, and –FS vs. Temperature
CIRCUIT INFORMATION
The AD7671 is a fast, low power, single-supply, precise 16-bit
analog-to-digital converter (ADC). The AD7671 features different
modes to optimize performances according to the applications.
In Warp Mode, the AD7671 is capable of converting 1,000,000
samples per second (1 MSPS).
The AD7671 provides the user with an on-chip track-and-hold,
successive approximation ADC that does not exhibit any pipeline
or latency, making it ideal for multiple multiplexed channel
applications.
It is specified to operate with both bipolar and unipolar input
ranges by changing the connection of its input resistive scaler.
The AD7671 can be operated from a single 5 V supply and be
interfaced to either 5 V or 3 V digital logic. It is housed in a
48-lead LQFP package or a 48-lead LFCSP package that com-
bines space savings and flexible configurations as either serial
or parallel interface. The AD7671 is a pin-to-pin compatible
upgrade of the AD7665 and AD7664.
REV. C
AD7671
–12–
Modes of Operation
The AD7671 features three modes of operation, Warp, Normal,
and Impulse. Each of these modes is more suitable for specific
applications.
The Warp Mode allows the fastest conversion rate up to 1 MSPS.
However, in this mode, and this mode only, the full specified accu-
racy is guaranteed only when the time between conversion does
not exceed 1 ms. If the time between two consecutive conversions
is longer than 1 ms, for instance, after power-up, the first conver-
sion result should be ignored. This mode makes the AD7671 ideal
for applications where both high accuracy and fast sample rate
are required.
The Normal Mode is the fastest mode (800 kSPS) without any limi-
tation about the time between conversions. This mode makes the
AD7671 ideal for asynchronous applications such as data acquisi-
tion systems, where both high accuracy and fast sample rate are
required.
The Impulse Mode, the lowest power dissipation mode, allows
power saving between conversions. The maximum throughput in
this mode is 666 kSPS. When operating at 100 SPS, for example,
it typically consumes only 15 mW. This feature makes the AD7671
ideal for battery-powered applications.
Transfer Functions
Using the OB/2C digital input, the AD7671 offers two output
codings: straight binary and twos complement. The ideal transfer
characteristic for the AD7671 is shown in Figure 4 and Table III.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE – Straight Binary
ANALOG INPUT
+FS – 1.5 LSB
+FS – 1 LSB
–FS + 1 LSB–FS
–FS + 0.5 LSB
Figure 4. ADC Ideal Transfer Function
CONVERTER OPERATION
The AD7671 is a successive approximation analog-to-digital
converter based on a charge redistribution DAC. Figure 3 shows
the simplified schematic of the ADC. The input analog signal is
first scaled down and level shifted by the internal input resistive
scaler, which allows both unipolar ranges (0 V to 2.5 V, 0 V to 5 V,
and 0 V to 10 V) and bipolar ranges (±2.5 V, ±5 V, and ±10 V).
The output voltage range of the resistive scaler is always 0 V to
2.5 V. The capacitive DAC consists of an array of 16 binary
weighted capacitors and an additional “LSB” capacitor. The
comparator’s negative input is connected to a “dummy” capacitor
of the same value as the capacitive DAC array.
During the acquisition phase, the common terminal of the array
tied to the comparator’s positive input is connected to AGND via
SW
A
. All independent switches are connected to the output of the
resistive scaler. Thus, the capacitor array is used as a sampling
capacitor and acquires the analog signal. Similarly, the dummy
capacitor acquires the analog signal on INGND input.
When the acquisition phase is complete and the CNVST input goes
or is LOW, a conversion phase is initiated. When the conversion
phase begins, SW
A
and SW
B
are opened first. The capacitor array
and the dummy capacitor are then disconnected from the inputs and
connected to the REFGND input. Therefore, the differential
voltage between the output of the resistive scaler and INGND
captured at the end of the acquisition phase is applied to the
comparator inputs, causing the comparator to become unbalanced.
By switching each element of the capacitor array between REFGND
or REF, the comparator input varies by binary weighted voltage
steps (V
REF
/2, V
REF
/4 . . .V
REF
/65,536). The control logic toggles
these switches, starting with the MSB first, in order to bring the
comparator back into a balanced condition. After the completion
of this process, the control logic generates the ADC output code
and brings BUSY output LOW.
SW
A
COMP
SW
B
IND 4R
REF
REFGND
LSB
MSB
32,768C
INGND
16,384C 4C 2C CC
CONTROL
LOGIC
SWITCHES
CONTROL
BUSY
OUTPUT
CODE
INC 4R
INA R
INB 2R
CNVST
65,536C
Figure 3. ADC Simplified Schematic
REV. C
AD7671
–13–
TYPICAL CONNECTION DIAGRAM
Figure 5 shows a typical connection diagram for the AD7671. Different circuitry shown on this diagram is optional and is discussed below.
100nF
10F100nF 10F
AVDD
10F100nF
AGND DGND DVDD OVDD OGND
SER/PAR
CNVST
BUSY
SDOUT
SCLK
RD
CS
RESET
PD
REFGND
CREF
2.5V REF REF
20
D
CLOCK
AD7671
C/P/DSP
SERIAL
PORT
DIGITAL SUPPLY
(3.3V OR 5V)
ANALOG
SUPPLY
(5V)
DVDD
OB/2C
NOTE 8
BYTESWAP
DVDD
50k
100nF
1M
INA
100nF
U2
IND
INGND
ANALOG
INPUT
(10V)
CC
2.7nF
U1
15
10F
NOTE 2
NOTE 1
NOTE 3
NOTE 7
NOTE 4
50
INC
INB
NOTE 6
NOTES
1. SEE VOLTAGE REFERENCE INPUT SECTION.
2. WITH THE RECOMMENDED VOLTAGE REFERENCES, CREF IS 47F. SEE VOLTAGE REFERENCE INPUT SECTION.
3. OPTIONAL CIRCUITRY FOR HARDWARE GAIN CALIBRATION.
4. FOR BIPOLAR RANGE ONLY. SEE SCALER REFERENCE INPUT SECTION.
5. THE AD8021 IS RECOMMENDED. SEE DRIVER AMPLIFIER CHOICE SECTION.
6. WITH 0V TO 2.5V RANGE ONLY. SEE ANALOG INPUTS SECTION.
7. OPTION. SEE POWER SUPPLY SECTION.
8. OPTIONAL LOW JITTER CNVST. SEE CONVERSION CONTROL SECTION.
+
+
+
++ +
+
AD8031
AD8021
50
ADR421
NOTE 5
WARP
IMPULSE
Figure 5. Typical Connection Diagram (
±
10 V Range Shown)
Table III. Output Codes and Ideal Input Voltages
Digital Output
Code (Hexa)
Straight Twos
Description Analog Input Binary Complement
Full-Scale Range
1
±10 V ±5 V ±2.5 V 0 V to 10 V 0 V to 5 V 0 V to 2.5 V
Least Significant Bit 305.2 mV152.6 mV76.3 mV152.6 mV76.3 mV38.15 mV
FSR – 1 LSB 9.999695 V 4.999847 V 2.499924 V 9.999847 V 4.999924 V 2.499962 V FFFF
2
7FFF
2
Midscale + 1 LSB 305.2 mV152.6 mV76.3 mV5.000153 V 2.570076 V 1.257038 V 8001 0001
Midscale 0 V 0 V 0 V 5 V 2.5 V 1.25 V 8000 0000
Midscale – 1 LSB –305.2 mV–152.6 mV–76.3 mV4.999847 V 2.499924 V 1.249962 V 7FFF FFFF
–FSR + 1 LSB –9.999695 V –4.999847 V –2.499924 V 152.6 mV76.3 mV38.15 mV0001 8001
–FSR –10 V –5 V –2.5 V 0 V 0 V 0 V 0000
3
8000
3
NOTES
1
Values with REF = 2.5 V. With REF = 3 V, all values will scale linearly.
2
This is also the code for an overrange analog input.
3
This is also the code for an underrange analog input.
REV. C
AD7671
–14–
Analog Inputs
The AD7671 is specified to operate with six full-scale analog input
ranges. Connections required for each of the four analog inputs,
IND, INC, INB, and INA, and the resulting full-scale ranges
are shown in Table I. The typical input impedance for each
analog input range is also shown.
Figure 6 shows a simplified analog input section of the AD7671.
The four resistors connected to the four analog inputs form a
resistive scaler that scales down and shifts the analog input range
to a common input range of 0 V to 2.5 V at the input of the
switched capacitive ADC.
INC
INB
INA
4R
2R
R
IND
4R
AGND
AVDD
R1
CS
R =
Figure 6. Simplified Analog Input
By connecting the four inputs INA, INB, INC, and IND to the
input signal itself, the ground, or a 2.5 V reference, other analog
input ranges can be obtained.
The diodes shown in Figure 6 provide ESD protection for the
four analog inputs. The inputs INB, INC, and IND have a high
voltage protection (–11 V to +30 V) to allow a wide input voltage
range. Care must be taken to ensure that the analog input signal
never exceeds the absolute ratings on these inputs, including
INA (0 V to 5 V). This will cause these diodes to become forward-
biased and start conducting current. These diodes can handle
a forward-biased current of 120 mA maximum. For instance,
when using the 0 V to 2.5 V input range, these conditions could
eventually occur on the input INA when the input buffer’s (U1)
supplies are different from AVDD. In such cases, an input buffer
with a short-circuit current limitation can be used to protect the part.
This analog input structure allows the sampling of the differen-
tial signal between the output of the resistive scaler and INGND.
Unlike other converters, the INGND input is sampled at the
same time as the inputs. By using this differential input, small
signals common to both inputs are rejected as shown in Figure 7,
which represents the typical CMRR over frequency. For instance,
by using INGND to sense a remote signal ground, the difference of
ground potentials between the sensor and the local ADC ground
is eliminated. During the acquisition phase for ac signals, the
AD7671 behaves like a one-pole RC filter consisting of the
equivalent resistance of the resistive scaler R/2 in series with R1
and C
S
. The resistor R1 is typically 100 W and is a lumped
component made up of some serial resistors and the on resis-
tance of the switches.
The capacitor C
S
is typically 60 pF and is mainly the ADC
sampling capacitor. This one-pole filter with a typical –3 dB
cutoff frequency of 9.6 MHz reduces undesirable aliasing effects
and limits the noise coming from the inputs.
40
35
50
45
60
55
70
65
75
1 10 100 1000 10000
CMRR – dB
FREQUENCY – kHz
Figure 7. Analog Input CMRR vs. Frequency
Except when using the 0 V to 2.5 V analog input voltage range,
the AD7671 has to be driven by a very low impedance source to
avoid gain errors. That can be done by using a driver amplifier
whose choice is eased by the primarily resistive analog input
circuitry of the AD7671.
When using the 0 V to 2.5 V analog input voltage range, the input
impedance of the AD7671 is very high so the AD7671 can be
driven directly by a low impedance source without gain error.
That allows, as shown in Figure 5, putting an external one-pole
RC filter between the output of the amplifier output and the
ADC analog inputs to even further improve the noise filtering
done by the AD7671 analog input circuit. However, the source
impedance has to be kept low because it affects the ac perfor-
mances, especially the total harmonic distortion (THD). The
maximum source impedance depends on the amount of total THD
that can be tolerated. The THD degradation is a function of the
source impedance and the maximum input frequency as shown
in Figure 8.
FREQUENCY – kHz
–110
0 100
THD – dB
–100
–90
–80
–70
1000
R = 100
R = 50
R = 11
Figure 8. THD vs. Analog Input Frequency and Input
Resistance (0 V to 2.5 V Only)
REV. C
375 Ω
AD7671
–15–
Driver Amplifier Choice
Although the AD7671 is easy to drive, the driver amplifier needs
to meet at least the following requirements:
∑
The driver amplifier and the AD7671 analog input circuit
must be able, together, to settle for a full-scale step the capaci-
tor array at a 16-bit level (0.0015%). In the amplifier’s data
sheet, the settling at 0.1% to 0.01% is more commonly speci-
fied. It could significantly differ from the settling time at
16-bit level and it should therefore be verified prior to the
driver selection. The tiny op amp AD8021, which combines
ultralow noise and a high gain bandwidth, meets this settling
time requirement even when used with a high gain up to 13.
∑
The noise generated by the driver amplifier needs to be kept
as low as possible in order to preserve the SNR and transi-
tion noise performance of the AD7671. The noise coming
from the driver is first scaled down by the resistive scaler
according to the analog input voltage range used and is then
filtered by the AD7671 analog input circuit one-pole, low-
pass filter made by (R/2 + R1) and C
S
. The SNR degradation
due to the amplifier is
SNR
fNe
FSR
LOSS
dB
N
=
+Ê
Ë
Áˆ
¯
˜
Ê
Ë
Á
Á
Á
Á
Á
ˆ
¯
˜
˜
˜
˜
˜
20 28
784 2
25
3
2
LOG
p
–
.
where:
f
–3 dB
is the –3 dB input bandwidth in MHz of the AD7671
(9.6 MHz) or the cutoff frequency of the input filter if
any used (0 V to 2.5 V range).
Nis the noise factor of the amplifier (1 if in buffer
configuration).
e
N
is the equivalent input noise voltage of the op amp
in nV/冪Hz.
FSR is the full-scale span (i.e., 5 V for ±2.5 V range).
For instance, when using the 0 V to 5 V range, a driver like
the AD8021, with an equivalent input noise of 2 nV/冪Hz and
configured as a buffer, thus with a noise gain of 1, the SNR
degrades by only 0.08 dB.
∑
The driver needs to have a THD performance suitable to that
of the AD7671. TPC 11 gives the THD versus frequency
that the driver should preferably exceed.
The AD8021 meets these requirements and is usually appropriate
for almost all applications. The AD8021 needs an external com-
pensation capacitor of 10 pF. This capacitor should have good
linearity as an NPO ceramic or mica type.
The AD8022 could also be used where a dual version is needed
and a gain of 1 is used.
The AD829 is another alternative where high frequency (above
100 kHz) performance is not required. In a gain of 1, it requires
an 82 pF compensation capacitor.
The AD8610 is another option where low bias current is needed
in low frequency applications.
Voltage Reference Input
The AD7671 uses an external 2.5 V voltage reference.
The voltage reference input REF of the AD7671 has a dynamic
input impedance; it should therefore be driven by a low impedance
source with an efficient decoupling between REF and REFGND
inputs. This decoupling depends on the choice of the voltage
reference but usually consists of a 1 mF ceramic capacitor and a
low ESR tantalum capacitor connected to the REF and REFGND
inputs with minimum parasitic inductance. 47 mF is an appropriate
value for the tantalum capacitor when used with one of the
recommended reference voltages:
∑The low noise, low temperature drift ADR421 and AD780
voltage references
∑The low power ADR291 voltage reference
∑The low cost AD1582 voltage reference
For applications using multiple AD7671s, it is more effective to
buffer the reference voltage with a low noise, very stable op amp
like the AD8031.
Care should also be taken with the reference temperature coeffi-
cient of the voltage reference that directly affects the full-scale
accuracy if this parameter matters. For instance, a ±15 ppm/∞C
temperature coefficient of the reference changes the full scale
by ±1 LSB/∞C.
Note that V
REF
, as mentioned in the Specifications table, could
be increased to AVDD – 1.85 V. The benefit here is the increased
SNR obtained as a result of this increase. Since the input range
is defined in terms of V
REF
, this would essentially increase the
±REF range from ±2.5 V to ±3 V and so on with an AVDD
above 4.85 V. The theoretical improvement as a result of this
increase in reference is 1.58 dB (20 log [3/2.5]). Due to the
theoretical quantization noise, however, the observed improve-
ment is approximately 1 dB. The AD780 can be selected with a
3V reference voltage.
Scaler Reference Input (Bipolar Input Ranges)
When using the AD7671 with bipolar input ranges, the connec-
tion diagram in Figure 5 shows a reference buffer amplifier. This
buffer amplifier is required to isolate the REF pin from the signal
dependent current in the INx pin. A high speed op amp, such as the
AD8031, can be used with a single 5 V power supply without
degrading the performance of the AD7671. The buffer must have
good settling characteristics and provide low total noise within
the input bandwidth of the AD7671.
Power Supply
The AD7671 uses three sets of power supply pins: an analog 5 V
supply AVDD, a digital 5 V core supply DVDD, and a digital
input/output interface supply OVDD. The OVDD supply allows
direct interface with any logic working between 2.7 V and DVDD
+ 0.3 V. To reduce the number of supplies needed, the digital core
(DVDD) can be supplied through a simple RC filter from the
analog supply as shown in Figure 5. The AD7671 is independent
of power supply sequencing, once OVDD does not exceed DVDD
by more than 0.3 V, and thus free from supply voltage induced
latch-up. Additionally, it is very insensitive to power supply varia-
tions over a wide frequency range as shown in Figure 9.
REV. C
AD7671
–16–
75
70
65
60
55
50
45
40
35
1
PSRR – dB
FREQUENCY – kHz
10 100 1000 10000
Figure 9. PSRR vs. Frequency
POWER DISSIPATION
In Impulse Mode, the AD7671 automatically reduces its power
consumption at the end of each conversion phase. During the
acquisition phase, the operating currents are very low, which allows a
significant power savings when the conversion rate is reduced,
as shown in Figure 10. This feature makes the AD7671 ideal for
very low power battery applications.
This does not take into account the power, if any, dissipated by
the input resistive scaler, which depends on the input voltage
range used and the analog input voltage even in Power-Down
Mode. There is no power dissipated when the 0 V to 2.5 V is used
or when both the analog input voltage is 0 V and a unipolar range,
0 V to 5 V or 0 V to 10 V, is used.
It should be noted that the digital interface remains active even
during the acquisition phase. To reduce the operating digital
supply currents even further, the digital inputs need to be driven
close to the power rails (i.e., DVDD and DGND) and OVDD
should not exceed DVDD by more than 0.3 V.
100000
10000
1000
100
10
1
0.1
1 10 100 1000 10000 100000 1000000
POWER DISSIPATION – W
SAMPLING RATE – SPS
WARP/NORMAL
IMPULSE
Figure 10. Power Dissipation vs. Sample Rate
CONVERSION CONTROL
Figure 11 shows the detailed timing diagrams of the conversion
process. The AD7671 is controlled by the signal CNVST, which
initiates conversion. Once initiated, it cannot be restarted or
aborted, even by the power-down input PD, until the conversion
is complete. The CNVST signal operates independently of CS
and RD signals.
CNVST
BUSY
MODE
t2
t1
t3
t4
t5
t6
t7 t8
ACQUIRE CONVERT ACQUIRE CONVERT
Figure 11. Basic Conversion Timing
In Impulse Mode, conversions can be automatically initiated. If
CNVST is held LOW when BUSY is LOW, the AD7671 controls
the acquisition phase and then automatically initiates a new conver-
sion. By keeping CNVST LOW, the AD7671 keeps the conversion
process running by itself. It should be noted that the analog input
has to be settled when BUSY goes LOW. Also, at power-up,
CNVST should be brought LOW once to initiate the conversion
process. In this mode, the AD7671 could sometimes run slightly
faster than the guaranteed limits in the Impulse Mode of
666 kSPS. This feature does not exist in Warp or Normal Modes.
Although CNVST is a digital signal, it should be designed with
special care with fast, clean edges, and levels with minimum over-
shoot and undershoot or ringing. It is a good thing to shield the
CNVST trace with ground and also to add a low value serial
resistor (i.e., 50 W) termination close to the output of the
component that drives this line.
For applications where the SNR is critical, the CNVST signal
should have a very low jitter. To achieve this, some use a dedicated
oscillator for CNVST generation, or at least to clock it with a
high frequency low jitter clock as shown in Figure 5.
t
9
t
8
RESET
DATA BUS
BUSY
CNVST
Figure 12. RESET Timing
REV. C
AD7671
–17–
DIGITAL INTERFACE
The AD7671 has a versatile digital interface; it can be interfaced
with the host system by using either a serial or parallel interface.
The serial interface is multiplexed on the parallel data bus. The
AD7671 digital interface also accommodates both 3 V or 5 V logic
by simply connecting the OVDD supply pin of the AD7671 to the
host system interface digital supply. Finally, by using the OB/2C
input pin, straight binary and twos complement coding can be used.
The two signals CS and RD control the interface. When at least
one of these signals is HIGH, the interface outputs are in high
impedance. Usually, CS allows the selection of each AD7671 in
multicircuit applications and is held LOW in a single AD7671
design. RD is generally used to enable the conversion result on
the data bus.
t1
t3
t4
t11
CNVST
BUSY
DATA BUS
CS = RD = 0
t10
PREVIOUS CONVERSION DATA NEW DATA
Figure 13. Master Parallel Data Timing for Reading
(Continuous Read)
PARALLEL INTERFACE
The AD7671 is configured to use the parallel interface when the
SER/PAR is held LOW. The data can be read either after each
conversion, which is during the next acquisition phase, or during
the following conversion as shown, respectively, in Figures 14 and
15. When the data is read during the conversion, however, it is
recommended that it be read-only during the first half of the con-
version phase. That avoids any potential feedthrough between
voltage transients on the digital interface and the most critical
analog conversion circuitry.
RD
BUSY
CS
CURRENT
CONVERSION
DATA BUS
t12 t13
Figure 14. Slave Parallel Data Timing for Reading (Read
after Convert)
t1
CS = 0
CNVST,
RD
PREVIOUS
CONVERSION
t3
t12 t13
t4
BUSY
DATA BUS
Figure 15. Slave Parallel Data Timing for Reading (Read
during Convert)
The BYTESWAP pin allows a glueless interface to an 8-bit bus.
As shown in Figure 16, the LSB is output on D[7:0] and the
MSB is output on D[15:8] when BYTESWAP is LOW. When
BYTESWAP is HIGH, the LSB and MSB bytes are swapped and
the LSB is output on D[15:8] and the MSB is output on D[7:0].
By connecting BYTESWAP to an address line, the 16 data bits
can be read in two bytes on either D[15:8] or D[7:0].
CS
BYTE
PINS D[15:8] HI-Z HIGH BYTE LOW BYTE HI-Z
HI-Z HIGH BYTE
LOW BYTE HI-Z
t12 t12 t13
PINS D[7:0]
RD
Figure 16. 8-Bit Parallel Interface
SERIAL INTERFACE
The AD7671 is configured to use the serial interface when the
SER/PAR is held HIGH. The AD7671 outputs 16 bits of data,
MSB first, on the SDOUT pin. This data is synchronized with
the 16 clock pulses provided on the SCLK pin. The output data
is valid on both the rising and falling edge of the data clock.
SLAVE SERIAL INTERFACE
External Clock
The AD7671 is configured to accept an externally supplied
serial data clock on the SCLK pin when the EXT/INT pin is
held HIGH. In this mode, several methods can be used to read
the data. The external serial clock is gated by CS and the data
are output when both CS and RD are LOW. Thus, depending on
CS, the data can be read after each conversion or during the follow-
ing conversion. The external clock can be either a continuous or
discontinuous clock. A discontinuous clock can be either normally
HIGH or normally LOW when inactive. Figures 19 and 21
show the detailed timing diagrams of these methods.
REV. C
AD7671
–18–
t
3
BUSY
CS, RD
CNVST
SYNC
SCLK
SDOUT
t
28
t
29
t
14
t
18
t
19
t
20
t
21
t
24
t
26
t
27
t
23
t
22
t
16
t
15
123 141516
D15 D14 D2 D1 D0
X
EXT/INT = 0 RDC/SDIN = 0 INVSCLK = INVSYNC = 0
t
25
t
30
Figure 17. Master Serial Data Timing for Reading (Read after Convert)
EXT/INT = 0 RDC/SDIN = 1 INVSCLK = INVSYNC = 0
t3
t1
t17
t14 t19
t20 t21 t24 t26
t25
t27
t23
t22
t16
t15
D15 D14 D2 D1 D0X
12 3 141516
t18
BUSY
SYNC
SCLK
SDOUT
CS, RD
CNVST
Figure 18. Master Serial Data Timing for Reading (Read Previous Conversion during Convert)
MASTER SERIAL INTERFACE
Internal Clock
The AD7671 is configured to generate and provide the serial data
clock SCLK when the EXT/INT pin is held LOW. It also gener-
ates a SYNC signal to indicate to the host when the serial data is
valid. The serial clock SCLK and the SYNC signal can be inverted
if desired. Depending on RDC/SDIN input, the data can be read
after each conversion or during conversion. Figures 17 and 18
show the detailed timing diagrams of these two modes.
Usually, because the AD7671 is used with a fast throughput, the
mode master, read during conversion, is the most recommended
Serial Mode when it can be used.
In Read-during-Conversion Mode, the serial clock and data toggle
at appropriate instants, which minimizes potential feedthrough
between digital activity and the critical conversion decisions.
In Read-after-Conversion Mode, it should be noted that unlike
in other modes, the signal BUSY returns LOW after the 16 data
bits are pulsed out and not at the end of the conversion phase,
which results in a longer BUSY width.
While the AD7671 is performing a bit decision, it is important that
voltage transients not occur on digital input/output pins or degra-
dation of the conversion result could occur. This is particularly
important during the second half of the conversion phase because
REV. C
AD7671
–19–
CS, RD
SCLK
SDOUT D15 D14 D1 D0
D13
X15 X14 X13 X1 X0 Y15 Y14
BUSY
SDIN
INVSCLK = 0
t35
t36 t37
t31 t32
t16
t33
t34
X15 X14
X
123 14151617 18
EXT/INT = 1 RD = 0
Figure 19. Slave Serial Data Timing for Reading (Read after Convert)
the AD7671 provides error correction circuitry that can correct
for an improper bit decision made during the first half of the
conversion phase. For this reason, it is recommended that when
an external clock is being provided, it is a discontinuous clock
that is toggling only when BUSY is LOW or, more importantly,
that does not transition during the latter half of BUSY HIGH.
External Discontinuous Clock Data Read after Conversion
Though the maximum throughput cannot be achieved using this
mode, it is the most recommended of the serial slave modes.
Figure 19 shows the detailed timing diagrams of this method.
After a conversion is complete, indicated by BUSY returning LOW,
the result of this conversion can be read while both CS and RD
are LOW. The data is shifted out, MSB first, with 16 clock
pulses and is valid on both the rising and falling edge of the clock.
Among the advantages of this method, the conversion perfor-
mance is not degraded because there are no voltage transients
on the digital interface during the conversion process.
Another advantage is to be able to read the data at any speed up to
40 MHz, which accommodates both slow digital host interface
and the fastest serial reading.
Finally, in this mode only, the AD7671 provides a “daisy-chain”
feature using the RDC/SDIN input pin for cascading multiple
converters together. This feature is useful for reducing component
count and wiring connections when desired as, for instance, in
isolated multiconverter applications.
An example of the concatenation of two devices is shown in Fig-
ure 20. Simultaneous sampling is possible by using a common
CNVST signal. It should be noted that the RDC/SDIN input is
latched on the opposite edge of SCLK of the one used to shift out
the data on SDOUT. Therefore, the MSB of the “upstream”
converter just follows the LSB of the “downstream” converter
on the next SCLK cycle.
CNVST
CS
SCLK
SDOUTRDC/SDIN
BUSYBUSY
DATA
OUT
AD7671
#1
(DOWNSTREAM)
BUSY
OUT
CNVST
CS
SCLK
AD7671
#2
(UPSTREAM)
RDC/SDIN SDOUT
SCLK IN
CS IN
CNVST IN
Figure 20. Two AD7671s in a Daisy-Chain Configuration
External Clock Data Read during Conversion
Figure 21 shows the detailed timing diagrams of this method.
During a conversion, while both CS and RD are LOW, the result
of the previous conversion can be read. The data is shifted out,
MSB first, with 16 clock pulses and is valid on both the rising and
the falling edge of the clock. The 16 bits have to be read before the
current conversion is complete. If that is not done, RDERROR
is pulsed HIGH and can be used to interrupt the host interface
to prevent incomplete data reading. There is no daisy-chain feature
in this mode, and RDC/SDIN input should always be tied either
HIGH or LOW.
REV. C
AD7671
–20–
To reduce performance degradation due to digital activity, a fast
discontinuous clock of at least 25 MHz when Impulse Mode is
used, 32 MHz when Normal or 40 MHz when Warp Mode is
used, is recommended to ensure that all the bits are read during
the first half of the conversion phase. It is also possible to begin
to read the data after conversion and continue to read the last bits
even after a new conversion has been initiated. That allows the use
of a slower clock speed like 18 MHz in Impulse Mode, 21 MHz
in Normal Mode, and 26 MHz in Warp Mode.
MICROPROCESSOR INTERFACING
The AD7671 is ideally suited for traditional dc measurement
applications supporting a microprocessor and ac signal processing
applications interfacing to a digital signal processor. The AD7671
is designed to interface either with a parallel 8-bit or 16-bit wide
interface or with a general-purpose Serial Port or I/O Ports on a
microcontroller. A variety of external buffers can be used with
the AD7671 to prevent digital noise from coupling into the ADC.
The following sections illustrate the use of the AD7671 with an
SPI equipped microcontroller, the ADSP-21065L and ADSP-218x
signal processors.
SPI Interface (MC68HC11)
Figure 22 shows an interface diagram between the AD7671 and an
SPI-equipped microcontroller, such as the MC68HC11. To accom-
modate the slower speed of the microcontroller, the AD7671 acts as
a slave device and data must be read after conversion. This mode
also allows the daisy-chain feature. The convert command could be
initiated in response to an internal timer interrupt. The reading of
output data, one byte at a time if necessary, could be initiated in
response to the end-of-conversion signal (BUSY going low) using
an interrupt line of the microcontroller. The serial peripheral
interface (SPI) on the MC68HC11 is configured for Master Mode
(MSTR) = 1, Clock Polarity Bit (CPOL) = 0, Clock Phase Bit
(CPHA) = 1, and SPI interrupt enable (SPIE) = 1 by writing to
the SPI Control Register (SPCR). The IRQ is configured for edge-
sensitive-only operation (IRQE = 1 in the OPTION register).
IRQ
MC68HC11*
CNVST
AD7671*
BUSY
CS
MISO/SDI
SCK
I/O PORT
SDOUT
SCLK
INVSCLK
EXT/INT
DVDD
*ADDITIONAL PINS OMITTED FOR CLARITY
SER/PAR
RD
Figure 22. Interfacing the AD7671 to SPI Interface
ADSP-21065L in Master Serial Interface
As shown in Figure 23, the AD7671 can be interfaced to the
ADSP-21065L using the serial interface in Master Mode without
any glue logic required. This mode combines the advantages
of reducing the wire connections and the ability to read the
data during or after conversion at maximum speed transfer
(DIVSCLK[0:1] both low).
The AD7671 is configured for the Internal Clock Mode (EXT/INT
LOW) and acts therefore as the master device. The convert
command can be generated by either an external low jitter oscil-
lator or, as shown, by a FLAG output of the ADSP-21065L or by
a frame output TFS of one Serial Port of the ADSP-21065L, which
can be used like a timer. The Serial Port on the ADSP-21065L
is configured for external clock (IRFS = 0), rising edge active
(CKRE = 1), external late framed sync signals (IRFS = 0,
LAFS = 1, RFSR = 1), and active HIGH (LRFS = 0). The Serial
Port of the ADSP-21065L is configured by writing to its receive
control register (SRCTL)—see ADSP-2106x SHARC User’s
Manual. Because the Serial Port within the ADSP-21065L will
be seeing a discontinuous clock, an initial word reading has to
be done after the ADSP-21065L has been reset to ensure that
the Serial Port is properly synchronized to this clock during each
following data read operation.
CNVST
SDOUT
SCLK
D1 D0
XD15 D14 D13
12 3 141516
t3 t35
t36 t37
t31 t32
t16
BUSY
INVSCLK = 0
CS
EXT/INT = 1 RD = 0
Figure 21. Slave Serial Data Timing for Reading (Read Previous Conversion during Convert)
REV. C
AD7671
–21–
RFS
ADSP-21065L*
SHARC
CNVST
AD7671*
CS
SYNC
RD
DR
RCLK
FLAG OR TFS
SDOUT
SCLK
INVSYNC
INVSCLK
EXT/INT
RDC/SDIN
SER/PAR
DVDD
*ADDITIONAL PINS OMITTED FOR CLARITY
®
Figure 23. Interfacing to the ADSP-21065L Using
the Serial Master Mode
APPLICATION HINTS
Layout
The AD7671 has very good immunity to noise on the power
supplies as can be seen in Figure 9. However, care should still
be taken with regard to grounding layout.
The printed circuit board that houses the AD7671 should be
designed so the analog and digital sections are separated and con-
fined to certain areas of the board. This facilitates the use of ground
planes that can be easily separated. Digital and analog ground
planes should be joined in only one place, preferably underneath
the AD7671, or, at least, as close as possible to the AD7671. If
the AD7671 is in a system where multiple devices require analog-
to-digital ground connections, the connection should still be made at
one point only, a star ground point, which should be established
as close as possible to the AD7671.
It is recommended to avoid running digital lines under the device
as these will couple noise onto the die. The analog ground plane
should be allowed to run under the AD7671 to avoid noise
coupling. Fast switching signals like CNVST or clocks should
be shielded with digital ground to avoid radiating noise to other
sections of the board and should never run near analog signal
paths. Crossover of digital and analog signals should be avoided.
Traces on different but close layers of the board should run at right
angles to each other. This will reduce the effect of feedthrough
through the board.
The power supply lines to the AD7671 should use as large a trace
as possible to provide low impedance paths and reduce the effect of
glitches on the power supply lines. Good decoupling is also impor-
tant to lower the supplies impedance presented to the AD7671
and to reduce the magnitude of the supply spikes. Decoupling
ceramic capacitors, typically 100 nF, should be placed on all of
the power supply pins power supplies pins AVDD, DVDD, and
OVDD close to, and ideally right up against, these pins and
their corresponding ground pins. Additionally, low ESR 10 mF
capacitors should be located in the vicinity of the ADC to further
reduce low frequency ripple.
The DVDD supply of the AD7671 can be either a separate sup-
ply or come from the analog supply, AVDD, or from the digital
interface supply, OVDD. When the system digital supply is noisy,
or fast switching digital signals are present, it is recommended,
if no separate supply is available, to connect the DVDD digital
supply to the analog supply AVDD through an RC filter as shown
in Figure 5 and to connect the system supply to the interface
digital supply OVDD and the remaining digital circuitry. When
DVDD is powered from the system supply, it is useful to insert
a bead to further reduce high frequency spikes.
The AD7671 has five different ground pins: INGND, REFGND,
AGND, DGND, and OGND. INGND is used to sense the
analog input signal. REFGND senses the reference voltage and
should be a low impedance return to the reference because it carries
pulsed currents. AGND is the ground to which most internal ADC
analog signals are referenced. This ground must be connected
with the least resistance to the analog ground plane. DGND must
be tied to the analog or digital ground plane depending on the
configuration. OGND is connected to the digital system ground.
The layout of the decoupling of the reference voltage is important.
The decoupling capacitor should be close to the ADC and con-
nected with short and large traces to minimize parasitic inductances.
Evaluating the AD7671 Performance
A recommended layout for the AD7671 is outlined in the evalua-
tion board for the AD7671. The evaluation board package includes
a fully assembled and tested evaluation board, documentation,
and software for controlling the board from a PC via the Eval-
Control Board.
REV. C
AD7671 Data Sheet
Rev. C | Page 22 of 24
OUTLINE DIMENSIONS
Figure 1. 48-Lead Low Profile Quad Flat Package [LQFP]
(ST-48)
Dimensions shown in millimeters
Figure 2. 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
7 mm × 7 mm Body, Very Thin Quad
(CP-48-1)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
AD7671ASTZ −40°C to +85°C 48-Lead Low Profile Quad Flat Package [LQFP] ST-48
AD7671ASTZRL −40°C to +85°C 48-Lead Low Profile Quad Flat Package [LQFP] ST-48
AD7671ACPZ −40°C to +85°C 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-48-1
AD7671ACPZRL −40°C to +85°C 48-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-48-1
EVAL-AD7671EDZ Evaluation Board
EVAL-CED1Z Converter Evaluation and Development Board
1 Z = RoHS Compliant Part.
COMPL IANT TO JE DE C STANDARDS MS-026-BBC
TOP VIEW
(PINS DOWN)
1
12 13 25
24
36
37
48
0.27
0.22
0.17
0.50
BSC
LEAD PITCH
1.60
MAX
0.75
0.60
0.45
VIEW A
PIN 1
0.20
0.09
1.45
1.40
1.35
0.08
COPLANARITY
VIEW A
ROTATED 90° CCW
SEATING
PLANE
7°
3.5°
0°
0.15
0.05
9.20
9.00 SQ
8.80
7.20
7.00 SQ
6.80
051706-A
PIN 1
INDICATOR
TOP
VIEW 6.75
BSC SQ
7.00
BSC SQ
1
48
12
13
37
36
24
25
5.25
5.10 S Q
4.95
0.50
0.40
0.30
0.30
0.23
0.18
0.50 BS C
12° MAX
0.20 REF
0.80 MAX
0.65 TY P
1.00
0.85
0.80
5.50
REF
0.05 MAX
0.02 NOM
0.60 MAX
0.60 MAX PIN 1
INDICATOR
COPLANARITY
0.08
SEATING
PLANE
0.25 MIN
EXPOSED
PAD
(BOTTO M VIEW)
COM P LI ANT T O JEDE C STANDAR DS MO- 2 20-VKKD-2
080108-A
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE P IN CONFIGURATION AND
FUNCTI O N DES CR I P T IONS
SECTION OF THIS DATA SHEET.
Data Sheet AD7671
Rev. C | Page 23 of 24
REVISION HISTORY
4/12—Rev. B to Rev. C
Added Exposed Pad Notation to Pin Configuration ................... 5
Added Exposed Pad Notation to Pin Function Description
Table ................................................................................................... 7
Change to Figure 6 ......................................................................... 14
Updated Outline Dimensions ....................................................... 22
Changes to Ordering Guide .......................................................... 22
4/03—Rev. A to Rev. B.
Changes to PulSAR Selection Table ............................................... 1
Changes to Ordering Guide ........................................................... 5
Changes to Figure 5 ........................................................................ 13
Updated Outline Dimensions ....................................................... 22
5/02—Rev. 0 to Rev. A.
Edits to Features ................................................................................ 1
Edits to General Description ........................................................... 1
Chart Added to Product Highlights ............................................... 1
Edits to Specifications ................................................................. 2–3
Edits to Table I .................................................................................. 3
Edits to Absolute Maximum Ratings ............................................. 5
Edits to Ordering Guide .................................................................. 5
Edits to TPC 4 .................................................................................... 9
New TPC 9 ..................................................................................... 10
Addition of TPC 16 ........................................................................ 11
Edits to Table III ............................................................................ 13
Edits to Driver Amplifier Choice Section .................................. 15
New Voltage Reference Input Section ......................................... 15
New ST-48 Package Outline ........................................................ 22
Data Sheet AD7671
Rev. C | Page 24 of 24
NOTES
©2012 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D02567-0-/12(C)
