Datasheet

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)
RLINE1
RLINE2
RREF
IB1
VIN7/VREFN2
RLINE3
VIN6/VREFP2
VIN0
VIN1
VA
RTD
PT-100
IB1 =
1 mA
+
2.2 PF
0.1 PF
+
1 PF
0.1 PF
VIO
LMP90080
XIN/CLK
SCLK
CSB
SDO/DRDYB
SDI
Microcontroller
3V 3V
D2
OSC
51:
LMP90077, LMP90078, LMP90079, LMP90080
SNAS521F –JULY 2011–REVISED MARCH 2013 www.ti.com
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.
VIN Equation for Topology #2 (18)
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