Datasheet

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 I
PRECHG
out of BAT
for the duration of t
DET
. If the battery voltage does not rise above V
RCH
, it indicates that a battery has been
inserted, and a new charge cycle begins. If the voltage rises above V
RCH
, it is possible that a fully charged
battery has been inserted. To check for this, I
BAT(DET)
is pulled from the battery for t
DET
. If the voltage falls below
V
LOWV
, 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 V
BAT(REG)
and is able to source currents up to
I
CHG
or I
INmax
, 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 V
IN(LOW)
3. The device has entered thermal regulation because the IC junction temperature has exceeded T
J(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
Copyright © 2009, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Link(s): TPS65720 TPS65721