BQ24618_15 Datasheet, PDF (22/43 Pages) Texas Instruments – System Power Selector and Low

bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
Feature Description (continued)
VREF
VREF
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V_LTF
V_{LTF_HYS}
CHARGE SUSPENDED
TEMPERATURE RANGE
TO INITIATE CHARGE
CHARGE SUSPENDED
V_LTF
V_{LTF_HYS}
TEMPERATURE RANGE
DURING A CHARGE
CYCLE
V_HTF
CHARGE SUSPENDED
V_TCO
CHARGE SUSPENDED
GND
GND
Figure 14. TS Pin, Thermistor Sense Thresholds
Assuming a 103AT NTC thermistor on the battery pack as shown in Figure 19, the values of RT1 and RT2 can
be determined by using the following equations:
RT2 =
V_VREF
´ RTH_COLD
´
RTH_HOT
´
æ1
ç
è ^VLTF
-
1ö
÷
V_{TCO ø}
RTH_HOT
´
æ
ç
è
V_VREF
V_TCO
ö
-
1_÷
ø
-
RTH_COLD
´
æ
ç
V_VREF
- 1_÷ö
è ^VLTF ø
(8)
RT1 =
V_VREF
V_LTF
-1
1
1
+
RT2 RTH_COLD
(9)
For example, 103AT NTC thermistors are used to monitor the battery pack temperature. Selecting T_COLD = 0ºC
and T_{CUT_OFF} = 45ºC gives R_T2 = 430 kΩ and R_T1 = 9.31 kΩ. A small RC filter is suggested to use for system-
level ESD protection.
VREF
bq24618
TS
RT1
RT2
RTH
103AT
Figure 15. TS Resistor Network
8.3.19 Timer Fault Recovery
The bq24618 provides a recovery method to deal with timer fault conditions. The following summarizes this
method:
Condition 1: The battery voltage is above the recharge threshold and a time-out fault occurs.
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