LMP90080-Q1 Datasheet, PDF (45/65 Pages) Texas Instruments – Multi-Channel 16-Bit Sensor AFE with Background Calibration

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+
2.2 PF
3V
0.1 PF
VA
LMP90080-Q1
SNIS186A – MAY 2013 – REVISED JANUARY 2014
3V
0.1 PF
VIO
+
1 PF
RLINE1
RTD
PT-100
RLINE2
RLINE3
RREF
IB1
VIN0
IB1 =
1 mA
SCLK
CSB
SDO/DRDYB
SDI
LMP90080
D2
VIN1
VIN6/VREFP2
VIN7/VREFN2
XIN/CLK
51:
Microcontroller
OSC
Figure 66. Topology #2: 3-wire RTD Using 1 Current Source
Figure 66 shows the second topology for a 3-wire RTD application. Topology #2 shows the same connection as
topology #1, but without IB2. Although this topology eliminates a current source, it requires two channel
measurements as shown in Equation 18.
VIN0 = IB1 (RLINE1 + RTD + RLINE3 + RREF)
VIN1 = IB1 (RLINE3 + RREF)
VIN6 = IB1 (RREF)
CH0 = VIN0 - VIN1 = IB1 (RLINE1 + RTD)
CH1 = VIN1 - VIN6 = IB1 (RLINE3)
Assume RLINE1 = RLINE3, thus:
CH0 - CH1 = IB1 (RTD)
VIN Equation for Topology #2
(18)
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