Datasheet

ref
CC
ref
CC
V
meas
V
meas
V
ref
ref
V
–R × C × ln
N
=
N
–R × C × ln
meas meas
ref ref
N R
=
N R
meas
meas ref
ref
N
R = R ×
N
V
C
V
CC
0.25 × V
CC
Phase I:
Charge
Phase II:
Discharge
Phase III:
Charge
t
ref
Phase IV:
Discharge
t
meas
t
R
meas
R
ref
www.ti.com Comparator_A+ Operation
The thermistor measurement is based on a ratiometric conversion principle. The ratio of two capacitor
discharge times is calculated as shown in Figure 21-7.
Figure 21-7. Timing for Temperature Measurement Systems
The V
CC
voltage and the capacitor value should remain constant during the conversion, but are not critical
since they cancel in the ratio:
529
SLAU144J–December 2004–Revised July 2013 Comparator_A+
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