BQ24257 Datasheet, PDF (27/45 Pages) Texas Instruments – 2A Single Input I2C, Standalone Switch-Mode Li-Ion Battery Charger with Integrated Current Sense Resistor

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bq24257
bq24258
SLUSBG0B – FEBRUARY 2013 – REVISED JULY 2013
Watchdog Timer
In addition to the safety timer, the bq24257 contains a 50-second watchdog timer that monitors the host through
the I2C interface. Once a write is performed on the I2C interface, a watchdog timer is reset and started. The
watchdog timer can be disabled by writing “0” on WD_EN bit of register #1. Writing “1” on that bit enables it and
reset the timer.
If the watchdog timer expires, the IC enters DEFAULT mode where the default charge parameters are loaded
and charging continues. The I2C may be accessed again to re-initialize the desired values and restart the
watchdog timer as long as the safety timer has not expired. Once the safety timer expires, charging is disabled.
Thermal Regulation and Thermal Shutdown
During the charging process, to prevent overheat of the chip, bq2425x monitors the junction temperature, T_J, of
the die and begins to taper down the charge current once T_J reaches the thermal regulation threshold, TREG.
The charge current is reduced when the junction temperature increases about above T_REG. Once the charge
current is reduced, the system current is reduced while the battery supplements the load to supply the system.
This may cause a thermal shutdown of the IC if the die temperature rises too. At any state, if T_J exceeds
T_SHTDWN, bq2425x suspends charging and disables the buck converter. During thermal shutdown mode, PWM is
turned off, all timers are suspended, and a single 256 μs pulse is sent on the STAT and INT outputs and the
FAULT/STAT bits of the status registers are updated in the I2C. A new charging cycle begins when T_J falls below
TSHTDWN by approximately 10°C.
Copyright © 2013, Texas Instruments Incorporated
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