LTC4066 LINER [Linear Technology], LTC4066 Datasheet - Page 20

• Manufacturer Part Number: LTC4066
• Description: USB Power Controller and Li-Ion Linear Charger with Low Loss Ideal Diode
• Manufacturer: LINER [Linear Technology]

LTC4066/LTC4066-1
APPLICATIONS INFORMATION
NTC Thermistor
The battery temperature is measured by placing a negative
temperature coeffi cient (NTC) thermistor close to the bat-
tery pack. The NTC circuitry is shown in Figure 4. To use
this feature, connect the NTC thermistor (R
the NTC pin and ground and a resistor (R
NTC pin to V
value equal to the value of the chosen NTC thermistor at
25°C (this value is 10k for a Vishay NTHS0603N02N1002J
thermistor). The LTC4066/LTC4066-1 go into hold mode
when the resistance (R
to 0.41 times the value of R
which should be at 50°C. The hold mode freezes the timer
and stops the charge cycle until the thermistor indicates a
return to a valid temperature. As the temperature drops,
the resistance of the NTC thermistor rises. The LTC4066/
LTC4066-1 are designed to go into hold mode when the
value of the NTC thermistor increases to 2.82 times the
20
R
10k
R
10k
NOM
V
NTC
NTC
15
14
NTC
NTC
. R
0.29 • V
0.74 • V
NOM
0.1V
NTC
NTC
HOT
should be a 1% resistor with a
) of the NTC thermistor drops
–
+
–
+
+
–
NOM
(4a)
or approximately 4.1k,
NOM
TOO_COLD
TOO_HOT
NTC_ENABLE
NTC
LTC4066
) from the
) between
4066 F04a
Figure 4. NTC Circuits
value of R
NTHS0603N02N1002J thermistor, this value is 28.2k
which corresponds to approximately 0°C. The hot and cold
comparators each have approximately 3°C of hysteresis
to prevent oscillation about the trip point. Grounding the
NTC pin can disable the NTC function.
Thermistors
The LTC4066/LTC4066-1 NTC trip points were designed to
work with thermistors whose resistance-temperature char-
acteristics follow Vishay Dale’s “R-T Curve 2”. The Vishay
NTHS0603N02N1002J is an example of such a thermistor.
However, Vishay Dale has many thermistor products that
follow the “R-T Curve 2” characteristic in a variety of sizes.
Furthermore, any thermistor whose ratio of R
is about 7.0 will also work (Vishay Dale R-T Curve 2 shows
a ratio of R
R
121k
R1
13.3k
R
100k
NOM
V
NTC
NTC
15
14
NTC
NOM
COLD
. This resistance is R
to R
0.29 • V
0.74 • V
HOT
0.1V
NTC
NTC
of 2.815/0.4086 = 6.89).
–
+
–
+
+
–
(4b)
COLD
. For a Vishay
TOO_COLD
TOO_HOT
NTC_ENABLE
COLD
LTC4066
4055 F03b
to R
4066fc
HOT