4.8 kHz, Ultralow Noise, 24-Bit
Sigma-Delta ADC with PGA and AC Excitation
AD7195
Chromatography
FEATURES
PLC/DCS analog input modules
Data acquisition
Medical and scientific instrumentation
AC or DC sensor excitation
RMS noise: 8.5 nV at 4.7 Hz (gain = 128)
16 noise-free bits at 2.4 kHz (gain = 128)
Up to 22.5 noise-free bits (gain = 1)
Offset drift: 5 nV/°C
Gain drift: 1 ppm/°C
Specified drift over time
2 differential/4 pseudo differential input channels
Automatic channel sequencer
Programmable gain (1 to 128)
Output data rate: 4.7 Hz to 4.8 kHz
Internal or external clock
GENERAL DESCRIPTION
The AD7195 is a low noise, complete analog front end for high
precision measurement applications. It contains a low noise,
24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC).
The on-chip low noise gain stage means that signals of small
amplitude can be interfaced directly to the ADC. The AD7195
contains ac excitation, which is used to remove dc-induced
offsets from bridge sensors.
The device can be configured to have two differential inputs or
four pseudo differential inputs. The on-chip channel sequencer
allows several channels to be enabled, and the AD7195 sequentially
converts on each enabled channel. This simplifies communication
with the part. The on-chip 4.92 MHz clock can be used as the
clock source to the ADC or, alternatively, an external clock or
crystal can be used. The output data rate from the part can be
varied from 4.7 Hz to 4.8 kHz.
Simultaneous 50 Hz/60 Hz rejection
Power supply
AVDD: 4.75 V to 5.25 V
DVDD: 2.7 V to 5.25 V
Current: 6 mA
Temperature range: –40°C to +105°C
Package: 32-lead LFCSP
INTERFACE
The device has two digital filter options. The choice of filter
affects the rms noise/noise-free resolution at the programmed
output data rate, the settling time, and the 50 Hz/60 Hz rejec-
tion. For applications that require all conversions to be settled,
the AD7195 includes a zero latency feature.
3-wire serial
SPI, QSPI™, MICROWIRE™, and DSP compatible
Schmitt trigger on SCLK
APPLICATIONS
Weigh scales
The part operates with a 5 V analog power supply and a digital
power supply from 2.7 V to 5.25 V. It consumes a current of
6 mA. It is housed in a 32-lead LFCSP package.
Strain gage transducers
Pressure measurement
Temperature measurement
FUNCTIONAL BLOCK DIAGRAM
AV
DV
DD DGND
DD AGND
REFIN(+) REFIN(–)
REFERENCE
DETECT
AV
DD
AIN1
AIN2
AIN3
AIN4
DOUT/RDY
SERIAL
INTERFACE
MUX
DIN
Σ-Δ
ADC
PGA
AND
AINCOM
CONTROL
LOGIC
SCLK
CS
SYNC
BPDSW
AGND
TEMP
SENSOR
AC
CLOCK
CIRCUITRY
EXCITATION
CLOCK
AD7195
ACX1
ACX1
ACX2
ACX2 MCLK1 MCLK2
Figure 1.
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. 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
©2010 Analog Devices, Inc. All rights reserved.
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