BQ25872 Datasheet, PDF (59/68 Pages) Texas Instruments – Battery Switch Charger

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Typical Application (continued)
9.2.1 Design Requirements
PARAMETER
Input voltage range
Input current limit
Output voltage range
Table 37. Design Requirement
bq25872
SLUSCQ6 – OCTOBER 2016
VALUE
3 V to 6 V
0.1 A to 7.5 A
3 V to 4.975 V
9.2.2 Detailed Design Procedure
The bq25872 continuously monitors battery and adaptor connector temperature by measuring the voltage
between TS_BAT pin and TS_BUS pins and ground, typically determined by a negative temperature coefficient
thermistor and an external voltage divider. The device compares this voltage against its internal thresholds to
determine if charging is allowed. To initiate a charging cycle, both battery and connector temperatures must be
lower than the temperature threshold, else the device suspends charging and waits until both temperatures are
blow the threshold.
Assuming a 103 AT NTC thermistor is used on the battery pack, the values RT1 (connected between TS_X pin
to VREF) and RT2 (connected between TS_X and ground) can be determined by using the following equations.
11
RT2 = ^{VREF × RTHCOLD × RTHHOT × @VLTF F VTCO A}
RTH_HOT × @_VVTRCEOF F 1A F RTH_COLD × @^VVRLTEFF F 1A
RT1 =
V_REF
V_LTF
F
1
1
1
RT2 ⁺ RTH_COLD
where
•
RTH_cold and V_LTF are the resistance of NTC under the cold temperature and the corresponding TS_X pin
voltage when charge is allowed, RTH_hot and V_TCOare the resistance of NTC under the hot temperature and the
corresponding TS_X pin voltage when charge is allowed.
(1)
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