Datasheet

PRECHARGE CCFAST
CHARGE
CV TAPER
DONE
Battery
Voltage
Battery
Current
THERMAL
REGULATION
T
J(REG)
ICjunction
temperature,Tj
I
(TERM)
I
(PRECHG)
TERMCURRENT=1
V
O(REG)
I
O(CHG)
V
(LOWV)
TPS65720
TPS65721
SLVS979 –OCTOBER 2009 www.ti.com
Figure 25. Thermal Loop
TIMER FAULT
If the pre-charge timer expires before the battery voltage reaches V
LOWV
, the charger indicates a fault condition.
Additionally, if the battery current does not fall to ITERM before the fast-charge timer expires, a fault is indicated
by setting Bit <TIMER_FAULT>=1.
THERMAL REGULATION AND THERMAL SHUTDOWN
The charger contains a thermal regulation loop that monitors the die temperature. If the temperature exceeds
T
J(REG)
, the device automatically reduces the charging current to prevent the die temperature from increasing
further. In some cases, the die temperature continues to rise despite the operation of the thermal loop,
particularly under high VAC and heavy system load conditions. Under these conditions, if the die temperature
increases to T
J(OFF)
, the input FET Q1 is turned OFF. FET Q2 is turned ON to ensure that the battery still powers
the load on SYS. Once the device die temperature cools by T
J(OFF-HYS)
, the input FET Q1 is turned on and the
device returns to thermal regulation. Continuous over-temperature conditions result in the pulsing of the Q1 FET.
Note that this feature monitors the die temperature of the charger. This is not synonymous with ambient
temperature. Self-heating exists due to the power dissipated in the IC because of the linear nature of the battery
charging algorithm and the LDO mode for SYS.
BATTERY PACK TEMPERATURE MONITORING
The TPS65720 features an external battery pack temperature monitoring input. The TS input connects to the
NTC resistor 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
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Product Folder Link(s): TPS65720 TPS65721