DA6505.005
11 June 2018
SENSOR BRIDGE RESISTANCE TEMPERATURE SENSING
The MAS6505 supports temperature sensing using temperature dependency of sensor bridge resistance. This is
selected by setting TSENSOR=0 in the Temperature sensor configuration register (FB/7BHEX). In this configuration
the piezoresistive sensor bridge RS is connected into a Wheatstone resistor bridge configuration together with
four internal resistors R1, R2, R3 and R4. See Figure 13.
VDD
RS
R3
R4
R1
R2
NI
PI
VIN
GND
Figure 13. Temperature measurement circuit configuration in sensor bridge resistance temperature sensing
The formed Wheatstone bridge is usually balanced (output signal close to zero) at room reference temperature
using RSENSOR sensor bridge resistance trim bits in the Temperature sensor configuration register (FB/7BHEX).
See table 7 for register details. The temperature signal has following characteristics and it is the input signal for
the MAS6505 AFE in the temperature measurement.
1
1
VIN
(
T
)
= VDDS
−
Equation 15
R
RS
R4
1+TCS
(
(
T −TREF
)
R3
R4
1
+1
+
+1
R2
1+TCR
T −TREF
)
VDDS = sensor supply voltage; 1.68V typ
RS = sensor bridge resistance []
R1, 2, 3, 4 = internal resistors (see value in Electrical characteristics table on page 7) []
TCS = sensor resistance temperature coefficient [ppm/C]
TCR = internal resistor temperature coefficient [ppm/C]
TREF = reference temperature for resistor values (typically +25C) [C]
T = actual sensor temperature to be measured [C]
From equation 9 we see that the temperature signal has a rising temperature dependency vs. temperature when
the sensor resistance has a positive temperature coefficient TCS>0. With negative sensor resistance temperature
coefficient TCS<0 the signal has a falling temperature dependency vs. temperature. See signal illustrations in
Figure 14.
Figure 14. Temperature signals of positive and negative TC bridge resistance sensors
37 (44)
MAS [ MICRO ANALOG SYSTEMS ]
