LTC3559 Linear Technology, LTC3559 Datasheet - Page 14

• Manufacturer Part Number: LTC3559
• Description: Linear USB Battery Charger
• Manufacturer: Linear Technology

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LTC3559
APPLICATIONS INFORMATION
14
NTC Thermistor
The battery temperature is measured by placing a nega-
tive temperature coeffi cient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 3.
To use this feature, connect the NTC thermistor, R
between the NTC pin and ground, and a bias resistor, R
from V
value equal to the value of the chosen NTC thermistor at
25°C (R25). A 100k thermistor is recommended since
thermistor current is not measured by the battery charger
and its current will have to be considered for compliance
with USB specifi cations.
The battery charger will pause charging when the re-
sistance of the NTC thermistor drops to 0.54 times the
CC
to NTC. R
POWER
ON
NOM
1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS
NO CHARGE CURRENT
CHRG PULSES
should be a 1% resistor with a
30 MINUTE
TRICKLE CHARGE MODE
TIMEOUT
DEFECTIVE BATTERY
Figure 2. State Diagram of the Battery Charger Operation
BAT ≤ 2.9V
FAULT
BAT > 2.9V
NOM
4-HOUR TERMINATION TIMER RESETS
NTC
BATTERY CHARGING SUSPENDED
CHRG PULSES
DUVLO, UVLO AND SUSPEND
IF SUSP < 0.4V AND
FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
4-HOUR TERMINATION TIMER
BEGINS
CONSTANT CURRENT MODE
CONSTANT VOLTAGE MODE
,
,
V
V
BAT DROPS BELOW 4.1V
CC
CC
> 4V AND
> BAT + 130mV
value of R25 or approximately 54k (for a Vishay “Curve
1” thermistor, this corresponds to approximately 40°C). If
the battery charger is in constant voltage mode, the safety
timer will pause until the thermistor indicates a return to
a valid temperature.
As the temperature drops, the resistance of the NTC
thermistor rises. The battery charger is also designed
to pause charging when the value of the NTC thermistor
increases to 3.25 times the value of R25. For a Vishay
“Curve 1” thermistor, this resistance, 325k, 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 disables all
NTC functionality.
NTC FAULT
2.9V < BAT < 4.1V
NO FAULT
YES
NO
4-HOUR
TIMEOUT
CHRG HIGH IMPEDANCE
NO CHARGE CURRENT
CHRG HIGH IMPEDANCE
DISABLE MODE
STANDBY MODE
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