TPS65721 datasheet(20/50 Pages) TI

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PRECHARGE

CCFAST CHARGE

CV TAPER

DONE

Battery

Voltage

BatteryCurrent

TERMCURRENT=1

VBAT(REG)

IO(CHG)

VLOWV

I(PRECHG)

I(TERM)

TPS65720

TPS65721

SLVS979 – OCTOBER 2009

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Figure 24. Battery Charge

In the precharge phase, the battery is charged with the precharge current (IPRECHG). Once the battery voltage

crosses the VLOWV threshold, the battery is charged with the fast-charge current (ICHG). As the battery voltage

reaches VBAT(REG), the battery is held at a constant voltage of VBAT(REG) and the charge current tapers off

as the battery approaches full charge. When the battery current reaches ITERM, the CHG pin indicates charging

done by going high impedance. Note that termination detection is disabled whenever the charge rate is reduced

from the set point because of the actions of the thermal loop, the DPM loop, or the VIN(LOW) loop. The value of

the fast-charge current is set by the resistor connected from the ISET pin to GND, and is given by the equation:

ICHG = KISET/RISET

The charge current limit is adjustable up to 300mA. The valid resistor range is 1500

Ω to 11.25kΩ. Note that if

ICHG is programmed as greater than the input current limit, the battery does not charge at the rate of ICHG, but

at the slower rate of IACmax (minus the load current on the OUT pin, if any). In this case, the charger timers are

proportionately slowed down.

I-PRECHARGE

The value for the pre-charge current is defined with Bits <I_PRE1, I_PRE0> based on the charge current defined

with pin ISET and Bits <CH_SCL1, ICH_SCL0> in register CHCONFIG1. Pre-charge current is scaled to lower

currents in DPPM mode or when the charger is in thermal regulation.

ITERM

The value for the termination current threshold can be set in register CHGCONFIG1 using Bits <I_TERM1,

I_TERM0> based on the charge current defined with pin ISET and Bits <CH_SCL1, ICH_SCL0>. Termination

current is not scaled in DPPM mode or when the charger is in thermal regulation.

BATTERY DETECTION AND RECHARGE

The charger automatically detects if a battery is connected or removed. Once a charge cycle is complete, the

battery voltage is monitored. When the battery voltage falls below VRCH, the device determines if the battery has

been removed. A current, IBAT(DET), is pulled from the battery for a duration tDET. If the voltage on the BAT pin

remains above VLOWV, it indicates that the battery is still connected, but has discharged. If <CH_EN>=1, the

charger is turned on again to top off the battery. During this recharge cycle, the CHG output remains

high-impedance. Recharge cycles are not indicated by the <CH_ACTIVE> Bit.

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