Datasheet

Thermal Regulation and Thermal Shutdown
bq25040
www.ti.com ...................................................................................................................................................... SLUS910B – MARCH 2009 – REVISED MARCH 2009
Table 2.
PG DEGLITCH (MEASURED FROM EVENT TO PG HIGH OR LOW)
CONDITION
bq25040 ENABLED (EN/SET low) bq25040 DISABLED (EN/SET high)
Entering OVP (V
IN
= 5.5V → 10V) 100 µ s 0
Leaving OVP (V
IN
= 10V → 5.5V) 450 µ s 500 µ s
Entering SLEEP (V
IN
= 5.5V → 3.6V) 32 ms 0
Leaving SLEEP(V
IN
= 3.6V → 5.5V) 500 µ s 500 µ s
Entering UVLO (V
IN
= 5.5V → 2.5V) 0 0
Leaving UVLO (V
IN
= 2.5V → 5.5V) 230 µ s 230 µ s
PG may be pulled up to any voltage rail less than the maximum rating on the PG output. Many LED applications
choose to pull up PG to the battery voltage. This is acceptable, however note that at low battery conditions, the
LED may appear dim. Another option is to pull up PG to the LDO output. This is also acceptable, however note
that the LDO current is not limited by the input current limit and the additional current may cause the bq25040
input current to exceed the maximum USB100 specification.
The bq25040 contain a thermal regulation loop that monitors the die temperature continuously. If the temperature
exceeds T
J(REG)
, the device automatically reduces the charging current to prevent the die temperature from
increasing further. The LDO current is not modified by thermal regulation. If the die temperature continues to rise
despite the operation of the thermal loop, and increases to T
J(OFF)
, the IC is turned off. Once the device die
temperature cools by T
J(OFF-HYS)
, the device turns on and returns to thermal regulation. Continuous
over-temperature conditions result in the pulsing of the load current. If the junction temperature of the device
exceeds T
J(OFF)
, the charge FET is turned off. The FET is turned back on when the junction temperature falls
below T
J(OFF)
– T
J(OFF-HYS)
.
Note that these features monitor the die temperature of the bq25040. 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. Battery NTC monitoring must be done by the host processor.
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