TPS65721 datasheet(22/50 Pages) TI

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PRECHARGE

CCFAST

CHARGE

CV TAPER

DONE

Battery

Voltage

Battery

Current

THERMAL

REGULATION

TJ(REG)

ICjunction

temperature,Tj

I(TERM)

I(PRECHG)

TERMCURRENT=1

VO(REG)

IO(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 VLOWV, 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

TJ(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 TJ(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 TJ(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, INTC 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 (VCOLD to VHOT), 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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TPS65721 Datasheet(PDF) 22 Page - Texas Instruments

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