BQ25895_16 Datasheet, PDF (32/67 Pages) Texas Instruments – Adjustable Voltage 3.1-A Boost Operation

bq25895
SLUSC88A – MARCH 2015 – REVISED MAY 2016
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8.3 Device Functional Modes
8.3.1 Host Mode and Default Mode
The device is a host controlled charger, but it can operate in default mode without host management. In default
mode, the device can be used an autonomous charger with no host or while host is in sleep mode. When the
charger is in default mode, WATCHDOG_FAULT bit is HIGH. When the charger is in host mode,
WATCHDOG_FAULT bit is LOW.
After power-on-reset, the device starts in default mode with watchdog timer expired, or default mode. All the
registers are in the default settings.
In default mode, the device keeps charging the battery with 12-hour fast charging safety timer. At the end of the
12-hour, the charging is stopped and the buck converter continues to operate to supply system load. Any write
command to device transitions the charger from default mode to host mode. All the device parameters can be
programmed by the host. To keep the device in host mode, the host has to reset the watchdog timer by writing 1
to WD_RST bit before the watchdog timer expires (WATCHDOG_FAULT bit is set), or disable watchdog timer by
setting WATCHDOG bits=00.
When the watchdog timer (WATCHDOG_FAULT bit = 1) is expired, the device returns to default mode and all
registers are reset to default values except IINLIM, VINDPM, VINDPM_OS, BATFET_RST_EN, BATFET_DLY,
and BATFET_DIS bits.
POR
watchdog timer expired
Reset registers
I2C interface enabled
Y
I2C Write?
N
Default Mode
Reset watchdog timer
Reset selective registers
Host Mode
Start watchdog timer
Host programs registers
Y
WD_RST bit = 1?
N
Y
N
I2C Write?
Y
Watchdog Timer
N
Expired?
Figure 25. Watchdog Timer Flow Chart
32
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