Datasheet

LTC4155
34
4155fc
curve 2 thermistor. The critically hot temperature indica-
tion is cleared when NTCVAL rises to decimal result 23.
This corresponds to
α
CRITICAL,RESET
= 0.341 and 55.5°C
for a Vishay curve 2 thermistor.
It is possible to modify the thermistor bias network to
adjust either one or two of the above temperature thresh-
olds. Because of the limited degrees of freedom in the
bias network, the remaining temperature threshold(s) will
then be constrained by the chosen network and thermistor
properties. See Alternate NTC Thermistors and Biasing in
the Applications Information section for implementation
details.
Overtemperature Battery Conditioner
Since Li-Ion batteries deteriorate with full voltage and
high temperature, the LTC4155 contains an automatic
battery conditioner circuit that reduces the battery volt-
age if both high temperature and high voltage are present
simultaneously.
OPERATION
Recall that battery charging is inhibited if the thermistor
temperature reaches 40°C. If the thermistor temperature
climbs above 60°C, and the battery conditioner circuit
is enabled, an internal load of approximately 125mA is
applied to BATSNS. Once the battery voltage drops to
3.9V, or the thermistor reading drops below 55.5°C, the
internal load is disabled. Battery charging resumes once
the thermistor temperature drops below 37°C.
When activated via the I
2
C port, the battery conditioner
operates whether or not external power is available,
charging has terminated or charging has been disabled
by I
2
C control. The battery conditioner is controlled by
the EN_BAT_CONDITIONER bit located at I
2
C sub address
0x00 (Table 6).
Note that this circuit can dissipate significant power inside
the LTC4155. To prevent an excessive temperature rise of
the LTC4155, the LTC4155 reduces discharge current as
needed to prevent a junction temperature rise above 120°C.