Comparator_A Operation
23-8
Comparator_A
The thermistor measurement is based on a ratiometric conversion principle.
The ratio of two capacitor discharge times is calculated as shown in
Figure 23−6.
Figure 23−6. Timing for Temperature Measurement Systems
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
The V
CC
voltage
and the capacitor value should remain constant during the
conversion, but are not critical since they cancel in the ratio:
N
meas
N
ref
+
–R
meas
C
ln
V
ref
V
CC
–R
ref
C
ln
V
ref
V
CC
N
meas
N
ref
+
R
meas
R
ref
R
meas
+
R
ref
N
meas
N
ref
Summary of Contents for MSP430x4xx Family
Page 1: ...MSP430x4xx Family 2007 Mixed Signal Products User s Guide SLAU056G ...
Page 2: ......
Page 6: ...vi ...
Page 114: ...3 76 RISC 16 Bit CPU ...
Page 304: ...5 20 FLL Clock Module ...
Page 340: ...7 8 Supply Voltage Supervisor ...
Page 348: ...8 8 16 Bit Hardware Multiplier ...
Page 372: ...9 24 32 Bit Hardware Multiplier ...
Page 400: ...10 28 DMA Controller ...
Page 428: ...13 10 Basic Timer1 ...
Page 466: ...15 24 Timer_A ...
Page 522: ...17 30 USART Peripheral Interface UART Mode ...
Page 544: ...18 22 USART Peripheral Interface SPI Mode ...
Page 672: ...23 12 Comparator_A ...
Page 692: ...24 20 LCD Controller ...
Page 746: ...26 28 ADC12 ...