AD7709
a
REV. PrA January 2001
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 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703  Analog Devices, Inc., 2001
16-Bit Sigma Delta ADC with Current Sources,
Switchable Reference Inputs and I/O Port
Preliminary Technical Data
PRELIMINARY TECHNICAL DATA
16-BIT SINGLE CHANNEL SIGMA DELTA-ADC
Factory Calibrated (field calibration not required)
Output settles in one conversion cycle (single conver
sion mode)
Programmable Gain Front End
16-bit No Missing Codes
13-bit Pk-Pk Resolution @ 20Hz, 20mV Range
16-bit Pk-PK Resolution @ 20Hz, 2.56V Range
INTERFACE
Three-Wire Serial
SPI
TM
, QSPI
TM
, MICROWIRE
TM
and DSP Compatible
Schmitt Trigger on SCLK
POWER
Specified for Single 3V and 5V operation
Normal : 2mA @ 3V
Powerdown : 20uA (32kHz Crystal Running)
On-Chip Functions
Rail-to-Rail Input Buffer and PGA
Switchable Reference Inputs
3 Configurable Current Sources
Low Side Power Swtches
Digital I/O Port
APPLICATIONS
Industrial Process Control
Instrumentation
Pressure Transducers
Portable Instrumentation
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The AD7709 is a complete analog front-end for low
frequency measurement applications. The AD7709
contains a 16-bit sigma delta ADC with PGA and can be
configured as 2 fully-differential input channels or 4
pseudo-differential input channels. Inputs signal ranges
from 20mV to 2.56V can be directly converted using the
AD7709. These signals can be converted directly from a
transducer without the need for signal conditioning. Other
on-chip features include three software configurable
current sources, switchable reference inputs, low side
power switches and a 4-bit digital I/O port.
The device operates from a 32kHz crystal with an on-
board PLL generating the required internal operating
frequency. The output data rate from the part is software
programmable. The pk-pk resolution from the part varies
with the programmed gain and output data rate.
The part operates from a single +3V or +5V supply.
When operating from +3V supplies, the power dissipation
for the part is XmW. The AD7709 are housed in a 24-
pin SOIC and TSSOP packages.
fi SPIand QSPI are a Registered Trademark of Motorola Inc.
fi MICROWIRE is a Registered Trademark of National Semiconductor Corp.
FEATURES
XTAL1 XTAL2REFIN2(+) REFIN2(-)VDD
OSC.
&
PLL
REFIN1(+) REFIN1(-)
SW2/P2SW1/P1
GND
AD7709
I/O PORT
VDD
AIN1
IOUT 1
IOUT 2
AIN2
AIN3 / P3
AIN4 / P4
MUX
BUF
PGA
AINCOM
SERIAL
INTERFACE
&
CONTROL
LOGIC
DOUT
DIN
SCLK
CS
RDY
RESET
16-BIT
Σ−∆ ADC
I1 I2 I3
PWRGND