LTC3554 LINER [Linear Technology], LTC3554 Datasheet - Page 18

• Manufacturer Part Number: LTC3554
• Description: Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators
• Manufacturer: LINER [Linear Technology]

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