XR18910 Datasheet, PDF (17/19 Pages) Exar Corporation – 8:1 Sensor Interface Analog Front End

XR18910
Application Information (Continued)
Typical Application – 8:1 Bridge Sensor Interface
The XR18910 was designed to interface multiple bridge sensors with a microcontroller or FPGA as illustrated in Figure 24.
The bridge output signal is differential (V_O+ and V_O-). Ideally, the unloaded bridge output is zero (V_O+ and V_O- are identical).
However, in-exact resistive values result in a difference between V_O+ and V_O-. This bridge offset voltage can be substantial
and vary between sensors. The XR18910 provides the ability to calibrate the bridge offset on each of the 8 bridge sensors
using the on-board DAC.
BRIDGE 8
BRIDGE 1
V_CC
V_DD
6.8μF
+
6.8μF
+
0.1μF
BRDG VCC
0.1μF
VDD
LDO
IN8+
0.1μF
IN8-
INA /
OUT ^10k
PGA
ADC
µC
8:1
MUX
IN1+
IN1-
±560mV
OFFSET TRIM
10-BIT
DAC
PGA
I²C
CONTROL
V_DD
4.7k
SDA
SCL
10nF
V_DD
4.7k
XR18910
AGND
DGND
Figure 24. 8:1 Bridge Sensor Interface
Layout Considerations
General layout and supply bypassing play major roles in high frequency performance. Follow the steps below as a basis for
high frequency layout:
■■ Include 6.8µF and 0.1µF ceramic capacitors for power supply decoupling
■■ Place the 6.8µF capacitor within 0.75 inches of the power pin
■■ Place the 0.1µF capacitor within 0.1 inches of the power pin
■■ Connection to the exposed pad is not required. Exposed pad can be connected to ground (GND).
■■ Minimize all trace lengths to reduce series inductances
REV1A
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