Datasheet

AD7195
Rev. 0 | Page 25 of 44
ADC CIRCUIT INFORMATION
MCLK1 MCLK2
DV
DD DGND REFIN(+) REFIN(–)
AIN1
AIN2
AIN3
AIN4
AINCOM
BPDSW
AD7195
REFERENCE
DETECT
SERIAL
INTERFACE
AND
CONTROL
LOGIC
TEMP
SENSOR
AC
EXCITATION
CLOCK
CLOCK
CIRCUITRY
DOUT/RDY
DIN
SCLK
CS
SYNC
AV
DD
AV
DD
AGND
AGND
Σ-Δ
ADC
PGA
MUX
ACX1 ACX1 ACX2ACX2
08771-001
Figure 18. Block Diagram
OVERVIEW
The AD7195 is an ultralow noise ADC that incorporates a Σ-
modulator, a buffer, PGA, and on-chip digital filtering intended
for the measurement of wide dynamic range signals, such as
those in pressure transducers, weigh scales, and strain gage
applications. Figure 18 shows the block diagram for the part.
Analog Inputs
The device can be configured to have two differential or four
pseudo differential analog inputs. The analog inputs can be
buffered or unbuffered.
Multiplexer
The on-chip multiplexer increases the channel count of the
device. Because the multiplexer is included on chip, any
channel changes are synchronized with the conversion process.
PGA
The analog input signal can be amplified using the PGA. The
PGA allows gains of 1, 8, 16, 32, 64, and 128.
Reference Detect
The AD7195 is capable of monitoring the external reference. If
the reference is not present, a flag is set in the status register of
the device.
Burnout Currents
Two 500 nA burnout currents are included on-chip to detect
the presence of the external sensor.
Σ-Δ ADC and Filter
The AD7195 contains a fourth-order Σ- modulator followed
by a digital filter. The device offers the following filter options:
• Sinc
4
• Sinc
3
• Chop enabled/disabled
• Zero latency
AC Excitation
The AD7195 supports ac excitation of load cells. It provides the
four logic outputs needed to control the transistors in an ac
excited load cell design.
Serial Interface
The AD7195 has a 4-wire SPI. The on-chip registers are
accessed via the serial interface.
Clock
The AD7195 has an internal 4.92 MHz clock. Either this clock
or an external clock can be used as the clock source to the
AD7195. The internal clock can also be made available on a
pin if a clock source is required for external circuitry.
Temperature Sensor
The on-chip temperature sensor monitors the die temperature.
Calibration
Both internal and system calibration are included on chip; thus,
the user has the option of removing offset/gain errors internal
to the AD7195 only, or removing the offset/gain errors of the
complete end system.