Datasheet

LTC3559/LTC3559-1
14
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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
NTC
,
between the NTC pin and ground, and a bias resistor, R
NOM
,
from V
CC
to NTC. R
NOM
should be a 1% resistor with a
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
APPLICATIONS INFORMATION
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.
IF SUSP < 0.4V AND
V
CC
> 4V AND
V
CC
> BAT + 130mV
DUVLO, UVLO AND SUSPEND DISABLE MODE
1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS
TRICKLE CHARGE MODE
FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
CONSTANT CURRENT MODE
BATTERY CHARGING SUSPENDED
CHRG PULSES
NTC FAULT
NO CHARGE CURRENT
CHRG PULSES
DEFECTIVE BATTERY
4-HOUR TERMINATION TIMER
BEGINS
CONSTANT VOLTAGE MODE
NO CHARGE CURRENT
CHRG HIGH IMPEDANCE
STANDBY MODE
CHRG HIGH IMPEDANCE
3559 F02
BAT b 2.9V
BAT > 2.9V
2.9V < BAT < V
RECHRG
30 MINUTE
TIMEOUT
BAT DROPS BELOW V
RECHRG
4-HOUR TERMINATION TIMER RESETS
YES
NO FAULT
FAULT
NO
POWER
ON
4-HOUR
TIMEOUT
Figure 2. State Diagram of the Battery Charger Operation