Datasheet

MICRO
CONTROLLER
+IN
-IN
REFS
REFF
FB
OUT
+5V
1
2
3
4
5
6
7
VHSER/VLPAR
V
-
VLSER/VHPAR
SCK/G2
SDI/G1
SDO/G0
8
9
10
11
12
13
14
V
+
LMP8358
CSB/SHDN
+3.3V
R
3
R
4
R
1
R
2
EMI
V
BRIDGE
ADC161S626
V
REF
CSB
SCLK
DOUT
V
A
V
IO
+5V
0.1 PF
+5V
MICRO
CONTROLLER
+3.3V
+
-
R
C
+
0.1 PF 10 PF
+
-
10k
10k
100pF
+5V
8k
2k
0.1 PF
+
0.1 PF 10 PF
+
0.1 PF
10 PF
LMP7701
LMP8358
SNOSB09B –APRIL 2010–REVISED MARCH 2013 www.ti.com
negative input of the ADC and the REFF and REFS pins of the LMP8358 can be set to +2.5V to set the signal at
the center of the supply. A resistor divider supplies +2.5V to the positive input of an LMP7701 set up in a buffer
configuration. The LMP7701 acts as a low impedance source for the REFF pin. The V
IO
and VHSER/VLPAR pins
should all be set to the same voltage as the microcontroller, +3.3V in this example. The VLSER/VHPAR pin
should be connected to ground. The resistor and capacitor between the LMP8358 and the ADC161S626 serve a
dual purpose. The capacitor is a charge reservoir for the sampling capacitor of the ADC. The resistor provides
isolation for the LMP8358 from the capacitive load. The values listed in the ADC161S626 datasheet are 180Ω for
the resistor and the 470pF for the capacitor. These two components also form a low pass filter of about 1.9MHz.
If a filter is needed to attenuate disturbance from the internal auto−zeroing at 12kHz and the ping−pong
frequency at 50kHz of the LMP8358 these values could be changed to 7870Ω and 0.01µF which will make a filter
with a corner of about 2kHz.
Figure 61. Differential Bridge Sensor
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