Datasheet

LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
18
3554123fd
NTC thermistors have temperature characteristics which
are indicated on resistance-temperature conversion tables.
The Vishay-Dale thermistor NTHS0603N011-N1003F, used
in the following examples, has a nominal value of 100k
and follows the Vishay curve 1 resistance-temperature
characteristic.
In the explanation below, the following notation is used.
R25 = Value of the thermistor at 25°C
R
NTC|COLD
= Value of thermistor at the cold trip point
R
NTC|HOT
= Value of the thermistor at the hot trip point
r
COLD
= Ratio of R
NTC|COLD
to R25
r
HOT
= Ratio of R
NTC|HOT
to R25
R
NOM
= Primary thermistor bias resistor (see Figure 2)
R1 = Optional temperature range adjustment resistor (see
Figure 2)
The trip points for the LTC3554’s temperature qualifica-
tion are internally programmed at 0.35 • V
BUS
for the hot
threshold and 0.76 • V
BUS
for the cold threshold.
OPERATION
Figure 1. Typical NTC Thermistor Circuit
Figure 2. NTC Thermistor Circuit with Additional Bias Resistor
+
+
R
NOM
100k
R
NTC
100k
NTC
V
BUS
NTC_ENABLE
3554 F01
NTC BLOCK
TOO_COLD
TOO_HOT
0.76 • V
BUS
(NTC RISING)
0.35 • V
BUS
(NTC FALLING)
0.017 • V
BUS
(NTC FALLING)
+
20
15
+
+
R
NOM
105k
R
NTC
100k
R1
12.7k
NTC
V
BUS
NTC_ENABLE
3554 F02
TOO_COLD
TOO_HOT
0.76 • V
BUS
(NTC RISING)
0.35 • V
BUS
(NTC FALLING)
0.017 • V
BUS
(NTC FALLING)
+
20
15