Datasheet

bq24072T
bq24075T, bq24079T
www.ti.com SLUS937A –DECEMBER 2009–REVISED APRIL 2010
The charge cycle after power-up, CE going low, or exiting OVP is indicated with the CHG output on (low - LED
on), whereas all refresh (subsequent) charges will result in the CHG output off (open – LED off). In addition, the
CHG signals timer faults by flashing at approximately 2Hz.
Table 2. PGOOD Status Indicator
INPUT STATE PGOOD OUTPUT
V
IN
< V
UVLO
Hi impedance
V
UVLO
< V
IN
< V
IN(DT)
Hi impedance
V
IN(DT)
< V
IN
< V
OVF
Low
V
IN
< V
OVP
Hi impedance
Table 3. CHG Status Indicator
CHARGE STATE CHG OUTPUT
Charging
Low (for first charge cycle)
Charging suspended by thermal loop, or DPPM loop
Safety timers expired Flashing at 2 Hz
Charging done
Recharging after termination
Hi impedance
IC disabled or no valid input power
Battery absent
THERMAL REGULATION AND THERMAL SHUTDOWN
The bq2407xT contain a thermal regulation loop that monitors the die temperature. If the temperature exceeds
T
J(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 V
IN
and heavy OUT system load conditions. Under these conditions, if the die temperature
increases to T
J(OFF)
, the input FET Q1 is turned OFF. FET Q2 is turned ON to ensure that the battery still powers
the load on OUT. Once the device die temperature cools by T
J(OFF-HYS)
, the input FET Q1 is turned on and the
device returns to thermal regulation. Continuous overtemperature conditions result in a "hiccup" mode. During
thermal regulation, the safety timers are slowed down proportionately to the reduction in current limit.
Note that this feature monitors the die temperature of the bq2407xT. 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 associated with OUT. A modified charge cycle with the thermal loop active is
shown in Figure 34. Battery termination is disabled during thermal regulation.
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