BQ24072 Datasheet, PDF (27/38 Pages) Texas Instruments – 1.2A USB-FRIENDLY Li-Ion BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24072, bq24073
bq24074, bq24075
www.ti.com...................................................................................................................................... SLUS810A – SEPTEMBER 2008 – REVISED DECEMBER 2008
BATTERY PACK TEMPERATURE MONITORING
The bq2407x features an external battery pack temperature monitoring input. The TS input connects to the NTC
thermistor in the battery pack to monitor battery temperature and prevent dangerous over-temperature
conditions. During charging, I_NTC is sourced to TS and the voltage at TS is continuously monitored. If, at any
time, the voltage at TS is outside of the operating range (V_COLD to V_HOT), charging is suspended. The timers
maintain their values but suspend counting. When the voltage measured at TS returns to within the operation
window, charging is resumed and the timers continue counting. When charging is suspended due to a battery
pack temperature fault, the CHG pin remains low and continues to indicate charging.
For the bq24072 and bq24073, battery pack temperature sensing is disabled when termination is disabled (TD =
High) and the voltage at TS is greater than V_DIS(TS). For applications that do not require the TS monitoring
function, connect a 10kΩ resistor from TS to VSS to set the TS voltage at a valid level and maintain charging.
The allowed temperature range for 103AT-2 type thermistor is 0°C to 50°C. However, the user may increase the
range by adding two external resistors. See Figure 42 for the circuit details. The values for RT1 and RT2 are
calculated using the following equations:
RT1 = ^{-1500μA ´ (RHOT + RCOLD) ± 20 ´ 5625μA2 ´ (RCOLD-RHOT)2 + 105μW ´ (RCOLD - RHOT)}
3000μA
(2)
RT2 =
1 V ´ (R1 + RHOT)
250 μA ´ RT1 + 250 μA ´ RHOT - 1 V
(3)
RHOT and RCOLD are the thermistor resistance at the desired hot and cold temperatures, respectively. Note
that the temperature window cannot be tightened more than using only the thermistor connected to TS, it
can only be extended.
I_NTC
bq2407x
TS
+
V_COLD
+
V_HOT
RT1
TEMP
PACK+
RT2
PACK-
Figure 42. Extended TS Pin Thresholds
Copyright © 2008, Texas Instruments Incorporated
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