LTC3554-1_15 Datasheet, PDF (18/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554/LTC3554-1/
LTC3554-2/LTC3554-3
OPeration
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
20 ^VBUS
R_NOM
100k
NTC
15
NTC BLOCK
0.76 • V_BUS
(NTC RISING)
–
+
R_NTC
100k
–
0.35 • V_BUS
(NTC FALLING) ₊
+
0.017 • V_BUS
(NTC FALLING)
–
TOO_COLD
TOO_HOT
NTC_ENABLE
3554 F01
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.
20 ^VBUS
R_NOM
105k
0.76 • V_BUS
(NTC RISING)
–
NTC
15
+
R1
12.7k
R_NTC
100k
–
0.35 • V_BUS
(NTC FALLING) ₊
TOO_COLD
TOO_HOT
+
0.017 • V_BUS
(NTC FALLING)
–
NTC_ENABLE
3554 F02
Figure 2. NTC Thermistor Circuit with Additional Bias Resistor
Figure 1. Typical NTC Thermistor Circuit
18
3554123ff