3 V/5 V, 1 mW, 2-/3-Channel,
16-Bit, Sigma-Delta ADCs
AD7705/AD7706
FEATURES
FUNCTIONAL BLOCK DIAGRAM
V
AD7705: 2 fully differential input channel ADCs
AD7706: 3 pseudo differential input channel ADCs
16 bits no missing codes
DD
REF IN(–)
REF IN(+)
AD7705/AD7706
CHARGE
BALANCING
A/D CONVERTER
0.003% nonlinearity
Programmable gain front end: gains from 1 to 128
3-wire serial interface
ANALOG
INPUT
CHANNELS
Σ -Δ
MODULATOR
PGA
BUFFER
MAX
SPI®-, QSPI™-, MICROWIRE™-, and DSP-compatible
Schmitt-trigger input on SCLK
A = 1 ≈ 128
DIGITAL FILTER
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 maximum @ 3 V
Standby current 8 μA maximum
SERIAL INTERFACE
REGISTER BANK
16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages
MCLK IN
SCLK
CS
CLOCK
GENERATION
MCLK OUT
GENERAL DESCRIPTION
DIN
DOUT
The AD7705/AD7706 are complete analog front ends for low
frequency measurement applications. These 2-/3-channel devices
can accept low level input signals directly from a transducer and
produce serial digital output. The devices employ a Σ-Δ
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 pro-
grammed via an on-chip control register, allowing adjustment of
the filter cutoff and output update rate.
GND
DRDY RESET
Figure 1.
The AD7705/AD7706 devices, 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. The devices can accept bipolar
input ranges of 10 mV through 1.225 V. Therefore, the
AD7705/AD7706 devices perform all signal conditioning and
conversion for a 2-channel or 3-channel system.
The AD7705/AD7706 devices operate from a single 2.7 V to
3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully
differential analog input channels; the AD7706 features three
pseudo differential input channels.
The AD7705/AD7706 are ideal for use in smart, microcontroller,
or DSP-based systems. The devices feature a serial interface that
can be configured for 3-wire operation. Gain settings, signal
polarity, and update rate selection can be configured in software
using the input serial port. The parts contains self-calibration and
system calibration options to eliminate gain and offset errors on
the part itself or in the system. CMOS construction ensures very
low power dissipation, and the power-down mode reduces the
standby power consumption to 20 μW typ.
Both devices feature a differential reference input. Input signal
ranges of 0 mV to 20 mV through 0 V to 2.5 V can be
incorporated on both devices 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 AIN(−) inputs on the AD7705 and to the COMMON input
on the AD7706.
These parts are available in a 16-lead, wide body (0.3 inch),
plastic dual in-line package (DIP); a 16-lead, wide body
(0.3 inch), standard small outline (SOIC) package; and a low
profile, 16-lead, thin shrink small outline package (TSSOP).
Rev. C
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 registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2006 Analog Devices, Inc. All rights reserved.
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