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| LTC3559-1_15 Datasheet, PDF (14/24 Pages) Linear Technology – Linear USB Battery Charger with Dual Buck Regulators | |||
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LTC3559/LTC3559-1
APPLICATIONS INFORMATION
NTC Thermistor
The battery temperature is measured by placing a nega-
tive temperature coefï¬cient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 3.
To use this feature, connect the NTC thermistor, RNTC,
between the NTC pin and ground, and a bias resistor, RNOM,
from VCC to NTC. RNOM 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 speciï¬cations.
The battery charger will pause charging when the re-
sistance of the NTC thermistor drops to 0.54 times the
value of R25 or approximately 54k (for a Vishay âCurve
1â 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
âCurve 1â 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.
POWER
ON
14
FAULT
BAT b 2.9V
DUVLO, UVLO AND SUSPEND
NO
IF SUSP < 0.4V AND
VCC > 4V AND
VCC > BAT + 130mV
YES
DISABLE MODE
CHRG HIGH IMPEDANCE
NTC FAULT
BATTERY CHARGING SUSPENDED
CHRG PULSES
NO FAULT
2.9V < BAT < VRECHRG
STANDBY MODE
NO CHARGE CURRENT
CHRG HIGH IMPEDANCE
TRICKLE CHARGE MODE
BAT > 2.9V
1/10 FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
30 MINUTE TIMER BEGINS
CONSTANT CURRENT MODE
FULL CHARGE CURRENT
CHRG STRONG PULL-DOWN
4-HOUR
TIMEOUT
30 MINUTE
TIMEOUT
DEFECTIVE BATTERY
NO CHARGE CURRENT
CHRG PULSES
CONSTANT VOLTAGE MODE
4-HOUR TERMINATION TIMER
BEGINS
BAT DROPS BELOW VRECHRG
4-HOUR TERMINATION TIMER RESETS
3559 F02
Figure 2. State Diagram of the Battery Charger Operation
3559fb
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