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AD7708BRUZ-REEL

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P44
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD7708/AD7718
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2001
8-/10-Channel, Low Voltage,
Low Power, ⌺-⌬ ADCs
FUNCTIONAL BLOCK DIAGRAM
DVDD XTAL1 XTAL2
MUX
POS BUF
⌺-⌬ ADC*
AIN1
AIN2
AIN3
AIN4
PGA
OSC
AND
PLL
SERIAL
INTERFACE
AND
CONTROL
LOGIC
DOUT
DIN
SCLK
CS
RDY
RESET
AV DD
I/O PORT
AV DD
AD7708/ AD7718
DGND
P2 P1
REFIN2(+)/AIN9 REFIN1(+) REFIN2(–)/AIN10 REFIN1(–)
AINCOM
AIN5
AIN6
AIN7
AIN8
AGND
*AD7708 16-BIT ADC
*AD7718 24-BIT ADC
REFIN(+) REFIN(–)
NEG BUF
FEATURES
8-/10-Channel, High Resolution ⌺-⌬ ADCs
AD7708 Has 16-Bit Resolution
AD7718 Has 24-Bit Resolution
Factory-Calibrated
Single Conversion Cycle Setting
Programmable Gain Front End
Simultaneous 50 Hz and 60 Hz Rejection
VREF Select
™ Allows Absolute and Ratiometric
Measurement Capability
Operation Can Be Optimized for
Analog Performance (CHOP = 0) or
Channel Throughput (CHOP = 1)
INTERFACE
3-Wire Serial
SPI
TM
, QSPI
TM
, MICROWIRE
TM
, and DSP-Compatible
Schmitt Trigger on SCLK
POWER
Specified for Single 3 V and 5 V Operation
Normal: 1.28 mA Typ @ 3 V
Power-Down: 30 ␮A (32 kHz Crystal Running)
On-Chip Functions
Rail-to-Rail Input Buffer and PGA
2-Bit Digital I/O Port
APPLICATIONS
Industrial Process Control
Instrumentation
Pressure Transducers
Portable Instrumentation
Smart Transmitters
SPI and QSPI are trademarks of Motorola Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
VREF Select is a trademark of Analog Devices, Inc.
GENERAL DESCRIPTION
The AD7708/AD7718 are complete analog front-ends for low
frequency measurement applications. The AD7718 contains a
24-bit Σ-∆ ADC with PGA and can be configured as 4/5 fully-
differential input channels or 8/10 pseudo-differential input
channels. Two pins on the device are configurable as analog
inputs or reference inputs. The AD7708 is a 16-bit version of
the AD7718. Input signal ranges from 20 mV to 2.56 V can be
directly converted using these ADCs. Signals can be converted
directly from a transducer without the need for signal conditioning.
The device operates from a 32 kHz crystal with an on-board PLL
generating the required internal operating frequency. The output
data rate from the part is software programmable. The peak-to-
peak resolution from the part varies with the programmed gain
and output data rate.
The part operates from a single 3 V or 5 V supply. When operating
from 3 V supplies, the power dissipation for the part is 3.84 mW typ.
Both parts are pin-for-pin compatible allowing an upgradable
path from 16 to 24 bits without the need for hardware modifica-
tions. The AD7708/AD7718 are housed in 28-lead SOIC and
TSSOP packages.
REV. 0
–2–
AD7708/AD7718
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
FUNCTIONAL BLOCK DIAGRAM . . . . . . . . . . . . . . . . . 1
GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1
AD7718 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . 3
AD7708 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . 6
TIMING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . 9
ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . 10
ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . 12
PIN CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . . . 13
ADC CIRCUIT INFORMATION . . . . . . . . . . . . . . . . . . . 15
Signal Chain Overview (CHOP Enabled, CHOP = 0) . . . 15
ADC NOISE PERFORMANCE CHOP ENABLED
(CHOP = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Signal Chain Overview (CHOP Disabled CHOP = 1) . . . 19
ADC NOISE PERFORMANCE CHOP DISABLED
(CHOP = 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
ON-CHIP REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Communications Register . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Mode Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Operating Characteristics when Addressing the
Mode and Control Registers . . . . . . . . . . . . . . . . . . . . . . . 28
ADC Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Filter Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
I/O Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
ADC Data Result Register . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Unipolar Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Bipolar Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
ADC Offset Calibration Coefficient Registers . . . . . . . . . . . 31
ADC Gain Calibration Coefficient Register . . . . . . . . . . . . . 31
ID Register (ID) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
User Nonprogrammable Test Registers . . . . . . . . . . . . . . . . 31
Configuring the AD7708/AD7718 . . . . . . . . . . . . . . . . . . . . 32
DIGITAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
MICROCOMPUTER/MICROPROCESSOR
INTERFACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
AD7708/AD7718 to 68HC11 Interface . . . . . . . . . . . . . . . . 34
AD7708/AD7718-to-8051 Interface . . . . . . . . . . . . . . . . . . 35
AD7708/AD7718-to-ADSP-2103/ADSP-2105 Interface . . . 36
BASIC CONFIGURATION . . . . . . . . . . . . . . . . . . . . . . . . 36
Analog Input Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Single-Ended Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Chop Mode of Operation (CHOP = 0) . . . . . . . . . . . . . . . . 37
Nonchop Mode of Operation (CHOP = 1) . . . . . . . . . . . . . 38
Programmable Gain Amplifier . . . . . . . . . . . . . . . . . . . . . . . 38
Bipolar/Unipolar Configuration . . . . . . . . . . . . . . . . . . . . . . 38
Data Output Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Oscillator Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Reference Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
RESET Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Power-Down Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Grounding and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Programmable Logic Controllers . . . . . . . . . . . . . . . . . . . . . 41
Converting Single-Ended Inputs. . . . . . . . . . . . . . . . . . . . . 42
Combined Ratiometric and Absolute Value
Measurement System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Optimizing Throughput while Maximizing 50 Hz
and 60 Hz Rejection in a Multiplexed Data
Acquisition System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . 44
TABLE OF CONTENTS
REV. 0
–3–
AD7708/AD7718
Parameter B Grade Unit Test Conditions
AD7718 (CHOP DISABLED)
Output Update Rate 16.06 Hz min CHOP = 1
1.365 kHz max
No Missing Codes
2
24 Bits min
Resolution 13 Bits p-p ±20 mV Range, SF = 69
18 Bits p-p ±2.56 V Range, SF = 69
Output Noise and Update Rates See Tables in
ADC Description
Integral Nonlinearity ±10 ppm of FSR max 2 ppm Typical
Offset Error
3
Table VII µV typ Offset Error is in the order of the noise for the
programmed gain and update rate following a
calibration
Offset Error Drift vs. Temp
4
±200 nV/°C typ
Full-Scale Error
3
±10 µV typ
Gain Drift vs. Temp
4
±0.5 ppm/°C typ
Negative Full-Scale Error ±0.003 % FSR max
ANALOG INPUTS
Differential Input Full-Scale Voltage ±1.024 × REFIN/GAIN V nom REFIN Refers to Both REFIN1 and
REFIN2. REFIN = REFIN(+) –REFIN(–)
GAIN = 1 to 128
Absolute AIN Voltage Limits AGND + 100 mV V min AIN1–AIN10 and AINCOM with
AV
DD
– 100 mV V max NEGBUF = 1
Absolute AINCOM Voltage Limits AGND – 30 mV V min NEGBUF = 0
AV
DD
+ 30 mV V max
Analog Input Current AIN1–AIN10 and AINCOM with NEGBUF = 1
DC Input Current
2
±1 nA max
DC Bias Current Drift ±5pA/°C typ
AINCOM Input Current NEGBUF = 0
DC Input Current
2
±125 nA/V typ ±2.56 V Range
DC Bias Current Drift ±2 pA/V/°C typ
Normal-Mode Rejection
2
@ 50 Hz 100 dB min 50 Hz ± 1 Hz, SF Word = 82
@ 60 Hz 100 dB min 60 Hz ± 1 Hz, SF Word = 68
Common-Mode Rejection
@ DC 90 dB min 100 dB typ, Analog Input = 1 V,
Input Range = ±2.56 V
110 dB typ on ±20 mV Range
@ 50 Hz 100 dB typ 50 Hz ± 1 Hz, SF Word = 82
@ 60 Hz 100 dB typ 60 Hz ± 1 Hz, SF Word = 68
REFERENCE INPUTS (REFIN1 AND REFIN2)
REFIN(+) to REFIN(–) Voltage 2.5 V nom REFIN Refers to Both REFIN1 and REFIN2
REFIN(+) to REFIN(–) Range
2
1V min
AV
DD
V max
REFIN Common-Mode Range AGND – 30 mV V min
AV
DD
+ 30 mV V max
Reference DC Input Current 0.5 µA/V typ
Reference DC Input Current Drift ±0.1 nA/V/°C typ
Normal-Mode Rejection
2
@ 50 Hz 100 dB min 50 Hz ± 1 Hz, SF Word = 82
@ 60 Hz 100 dB min 60 Hz ± 1 Hz, SF Word = 68
Common-Mode Rejection Input Range = ±2.56 V
@ DC 100 dB typ Analog Input = 1 V. Input Range = ±2.56 V
@ 50 Hz 100 dB typ
@ 60 Hz 100 dB typ
AD7718 SPECIFICATIONS
1
(AV
DD
= 2.7 V to 3.6 V or 4.75 V to 5.25 V, DV
DD
= 2.7 V to 3.6 V or 4.75 V to 5.25 V,
REFIN(+) = 2.5 V; REFIN(–) = AGND; AGND = DGND = 0 V; XTAL1/XTAL2 = 32.768 kHz Crystal Input Buffer Enabled. All specifications T
MIN
to
T
MAX
unless otherwise noted.)
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P36P37-P39P40-P42P43-P44

AD7708BRUZ-REEL

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Buy AD7708BRUZ-REEL
Manufacturer:
Analog Devices Inc.
Description:
Analog to Digital Converters - ADC 16-Bit 8/10-Ch Low Vtg Low Pwr
Lifecycle:
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