Datasheet

LTC4095
10
4095fa
OPERATION
Figure 2. State Diagram of LTC4095 Operation
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 IN 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 LTC4095 and
its current will have to be considered for compliance with
USB specifi cations.
The LTC4095 will pause charging when the resistance of
the NTC thermistor drops to 0.54 times the 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 therm-
istor rises. The LTC4095 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
IN > 4V AND
IN > BAT + 165mV
DUVLO, UVLO AND SUSPEND SUSPEND/SHUTDOWN 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
BAT DROPS BELOW 0.105V
4 HOUR TERMINATION TIMER RESETS
CONSTANT VOLTAGE MODE
NO CHARGE CURRENT
CHRG HIGH IMPEDANCE
STANDBY MODE
CHRG HIGH IMPEDANCE
BAT > 2.9V
4095 F02
NO FAULT, BAT ≤ 2.9V
30 MINUTE
TIMEOUT
4 HOUR CHARGE
CYCLE BEGINS
2.9V < BAT < 4.105V
TRUE
4 HOUR
TIMEOUT
NO FAULT
FAULT
FALSE
POWER
ON