TPS65721 datasheet(21/50 Pages) TI

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TPS65720

TPS65721

www.ti.com

SLVS979 – OCTOBER 2009

If the BAT voltage falls below VLOWV during the battery detection test, it indicates that the battery has been

removed. The device then checks for battery insertion. The FET Q2 is turned on and sources IPRECHG out of BAT

for the duration of tDET. If the battery voltage does not rise above VRCH, it indicates that a battery has been

inserted, and a new charge cycle begins. If the voltage rises above VRCH, it is possible that a fully charged

battery has been inserted. To check for this, IBAT(DET) is pulled from the battery for tDET. If the voltage falls below

VLOWV, a battery is not present. The device continuously checks for the presence of a battery.

CHARGE TERMINATION ON/OFF

Charge termination can be disabled by setting the Bit <TERM_EN>=0. When termination is disabled, the device

goes through the pre-charge, fast-charge, and CV phases, then remains in the CV phase. During the CV phase,

the charger behaves like an LDO with an output voltage equal to VBAT(REG) and is able to source currents up to

ICHG or IINmax, whichever is less. Battery detection is not performed. The Bit <CH_ACTIVE>=0 once the current

falls below ITERM and does not go t o1 until the input power is toggled. When termination is disabled, the

pre-charge and fast-charge safety timers are also disabled. Battery pack temperature sensing (TS pin

functionality) is also disabled if Bit <TERM_EN>=0 and the TS pin is unconnected.

TIMERS

The charger in TPS65720 has internal safety timers for the pre-charge and fast-charge phases to prevent

potential damage to either the battery or the system. The default values for the timers can be changed in register

CHGCONFIG2.

The pre-charge timer and fast charge timer will run with their nominal speed defined in register CHCONFIG2 if

ICH_SCL[1,0]=01, which equals a charge current of 50% defined with the ISET resistor. If ICH_SCL[1,0] are set

to higher or lower fast- charge current, the fast charge timers and pre-charge timers are scaled automatically. For

instance, with ICH_SCL[1,0]=11, which equals 100% of fast charge current, the safety timers will time out in half

the time defined in register CHCONFIG2. Changing the pre-charge current with I_PRE[1,0] will not change the

pre-charge or fast-charge timers.

DYNAMIC TIMER FUNCTION

During the fast-charge phase, several events increase the timer durations.

1. The system load current activates the DPM loop which reduces the available charging current

2. The input current is reduced because the input voltage has fallen to VIN(LOW)

3. The device has entered thermal regulation because the IC junction temperature has exceeded TJ(REG)

During each of these events, the internal timers are slowed down proportionately to the reduction in charging

current. For example, if the charging current is reduced by half, the fast-charge timer is twice as long as

programmed.

A modified charge cycle with the thermal loop active is shown in Figure 25

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TPS65721 Datasheet(PDF) 21 Page - Texas Instruments