3 V/5 V, ؎10 V Input Range, 1 mW
3-Channel 16-Bit, Sigma-Delta ADC
a
AD7707
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Charge Balancing ADC
DV
AV
DD
DD
REF IN(–) REF IN(+)
16 Bits No Missing Codes
0.003% Nonlinearity
AD7707
CHARGE
BALANCING
A/D CONVERTER
High Level (؎10 V) and Low Level (؎10 mV) Input
Channels
True Bipolar ؎100 mV Capability on Low Level Input
Channels Without Requiring Charge Pumps
Programmable Gain Front End
Gains from 1 to 128
AIN1
AIN2
MUX
⌺ – ⌬
MODULATOR
LOCOM
PGA
BUF
30k⍀
5k⍀
AIN3
DIGITAL FILTER
A = 1Ϸ128
VBIAS
5k⍀
Three-Wire Serial Interface
SERIAL INTERFACE
REGISTER BANK
SPI™, QSPI™, MICROWIRE™ and DSP Compatible
Schmitt Trigger Input on SCLK
Ability to Buffer the Analog Input
2.7 V to 3.3 V or 4.75 V to 5.25 V Operation
Power Dissipation 1 mW max @ 3 V
Standby Current 8 A max
15k⍀
SCLK
HICOM
CS
30k⍀
DIN
MCLK IN
CLOCK
GENERATION
DOUT
MCLK OUT
20-Lead SOIC and TSSOP Packages
AGND
DGND
DRDY
RESET
GENERAL DESCRIPTION
The AD7707 is ideal for use in smart, microcontroller or DSP-
based systems. It features a serial interface that can be config-
ured for three-wire operation. Gain settings, signal polarity and
update rate selection can be configured in software using the
input serial port. The part contains self-calibration and system
calibration options to eliminate gain and offset errors on the
part itself or in the system.
The AD7707 is a complete analog front end for low frequency
measurement applications. This three-channel device can accept
either low level input signals directly from a transducer or high
level (±10 V) signals and produce a serial digital output. It
employs a sigma-delta conversion technique to realize up to
16 bits of no missing codes performance. The selected input
signal is applied to a proprietary programmable gain front end
based around an analog modulator. The modulator output is
processed by an on-chip digital filter. The first notch of this
digital filter can be programmed via an on-chip control register
allowing adjustment of the filter cutoff and output update rate.
CMOS construction ensures very low power dissipation, and the
power-down mode reduces the standby power consumption to
20 µW typ. These parts are available in a 20-lead wide body
(0.3 inch) small outline (SOIC) package and a low profile 20-lead
TSSOP.
The AD7707 operates from a single 2.7 V to 3.3 V or 4.75 V to
5.25 V supply. The AD7707 features two low level pseudo-
differential analog input channels, one high level input channel
and a differential reference input. Input signal ranges of 0 mV to
+20 mV through 0 V to +2.5 V can be accommodated on both
low level input channels when operating with a VDD of 5 V and a
reference of 2.5 V. They can also handle bipolar input signal
ranges of ±20 mV through ±2.5 V, which are referenced to the
LCOM input. The AD7707, with a 3 V supply and a 1.225 V
reference, can handle unipolar input signal ranges of 0 mV to
+10 mV through 0 V to +1.225 V. Its bipolar input signal ranges
are ±10 mV through ±1.225 V.
PRODUCT HIGHLIGHTS
1. The AD7707 consumes less than 1 mW at 3 V supplies and
1 MHz master clock, making it ideal for use in low power
systems. Standby current is less than 8 µA.
2. On-chip thin-film resistors allow ±10 V, ±5 V, 0 V to +10 V
and 0 V to +5 V high level input signals to be directly accom-
modated on the analog inputs without requiring split supplies
or charge-pumps.
3. The low level input channels allow the AD7707 to accept
input signals directly from a strain gage or transducer remov-
ing a considerable amount of signal conditioning.
The high level input channel can accept input signal ranges of
±10 V, ±5 V, 0 V to +10 V and 0 V to +5 V. The AD7707 thus
performs all signal conditioning and conversion for a three-
channel system.
4. The part features excellent static performance specifications
with 16 bits, no missing codes, ±0.003% accuracy and low
rms noise. Endpoint errors and the effects of temperature
drift are eliminated by on-chip calibration options, which
remove zero-scale and full-scale errors.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
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