Datasheet

PRECHARGE
CCFAST CHARGE CV TAPER
DONE
Battery
Voltage
BatteryCurrent
TERMCURRENT=1
V
BAT(REG)
I
O(CHG)
V
LOWV
I
(PRECHG)
I
(TERM)
TPS65720
TPS65721
SLVS979 –OCTOBER 2009 www.ti.com
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 1500Ω 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 V
LOWV
, 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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