AD7707_15 Datasheet, PDF (1/52 Pages) Analog Devices – 3-Channel 16-Bit, Sigma-Delta ADC

3 V/5 V, ±10 V Input Range, 1 mW
3-Channel 16-Bit, Sigma-Delta ADC
AD7707
FEATURES
Charge balancing ADC
16 bits, no missing codes
±0.003% nonlinearity
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
3-wire serial interface
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 at 3 V
Standby current 8 μA maximum
20-lead SOIC and TSSOP packages
GENERAL DESCRIPTION
The AD7707 is a complete analog front end for low frequency
measurement applications. This 3-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 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.
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 differen-
tial 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.
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 3-channel system.
The AD7707 is ideal for use in smart, microcontroller or DSP-
based systems. It features a serial interface that can be configured
Rev. B
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AIN1
AIN2
LOCOM
AIN3
VBIAS
FUNCTIONAL BLOCK DIAGRAM
DV_DD AV_{DD REF IN(–) REF IN(+)}
AD7707
CHARGE
BALANCING
A/D CONVERTER
MUX
BUF
PGA
Σ-Δ
MODULATOR
30kΩ
5kΩ
A = 1 ≈ 128
DIGITAL FILTER
5kΩ
HICOM
15kΩ
30kΩ
SERIAL INTERFACE
REGISTER BANK
MCLK IN
MCLK OUT
CLOCK
GENERATION
SCLK
CS
DIN
DOUT
AGND DGND
Figure 1.
DRDY RESET
for 3-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 calibra-
tion 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 typical. This part is available in a 20-lead wide body (0.3
inch) small outline (SOIC) package and a low profile 20-lead TSSOP.
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
removing a considerable amount of signal conditioning.
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.
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