XR18910 Datasheet, PDF (12/19 Pages) Exar Corporation – 8:1 Sensor Interface Analog Front End

Functional Block Diagram
V_CC
1.5V
Reference
LDO Enable
LDO Select ( 3V, 2.65V )
AGND
XR18910
LDO Output
Input 1 +/-
Input 2 +/-
Input 8 +/-
PGA
10-Bit Offset DAC
Output
VDD
SDA
SCL
I²C Serial Digital Interface
DGND
Figure 20. Functional Block Diagram
Application Information
The XR18910 sensor interface includes a 8:1 differential
multiplexer (MUX), a programmable gain instrumentation
amplifier, a 10-bit offset correction DAC and an LDO. An
I²C interface controls the many functions and features of the
XR18910. The XR18910 is designed to integrate multiple
bridge sensors with an ADC/MCU or FPGA.
Each bridge sensor connected to the XR18910 has its
own inherent offset that if not calibrated out can decrease
sensitivity and overall performance of the sensor system. The
on-board DAC introduces an offset into the instrumentation
amplifier to calibrate the offset voltage generated by the
sensors. An independent offset can be set for each of the
8 channels. Only the offset voltage of the active channel is
applied to the PGA.
The programmable gain instrumentation amplifier offers 8
selectable gains from 2V/V to 760V/V to amplify the signal
such that it falls within the input range of the ADC.
An integrated LDO provides a regulated voltage to power
the input bridge sensors and is selectable, between 3V and
2.65V. The LDO can be set to turn off when the XR18910 is
in sleep mode to save power.
The XR18910 also provides the ability to monitor the LDO
current. When the XR18910 is in current sense mode, an
internal 2:1 MUX allows a voltage proportional to the LDO
current to be present at the output. Once all channels have
been calibrated, the LDO current can be used to indirectly
monitor any voltage or resistive changes seen by the inputs.
The XR18910 also includes an internal 1.5V reference that
is used by the internal LDO circuitry and used to set the
reference voltage for the programmable gain instrumentation
amplifier.
During sleep mode, the analog components of the XR18910
are powered down for added power savings.
The XR18910 offers many functions, each controlled by the
I²C compatible serial interface:
■■ Input Selection
■■ Gain Selection
■■ Offset Correction
■■ LDO Enable/Select
■■ Current Sense Mode
■■ Sleep Mode (analog power down)
REV1A
12/19