BQ24298_15 Datasheet, PDF (26/51 Pages) Texas Instruments – bq24298 I2C Controlled 3A Single Cell USB Charger With Narrow VDC Power Path Management and Adjustable Voltage USB OTG

bq24298
SLUSC59 – APRIL 2015
www.ti.com
Device Functional Modes (continued)
When the charger is in default mode, REG09[7] is HIGH. When the charger is in host mode, REG09[7] is LOW.
After power-on-reset, the device starts in watchdog timer expiration state, or default mode. All the registers are in
the default settings. The device keeps charging the battery by default with 12-hour fast charging safety timer. At
the end of the 12 hours, the charging is stopped and the buck converter continues to operate to supply system
load.
Any write command to device transitions the device 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 REG01[6] before the watchdog timer expires (REG05[5:4]), or disable watchdog timer by setting
REG05[5:4] = 00.
When the host changes watchdog timer configuration (REG05[5:4]), it is recommended to first disable watchdog
by writing 00 to REG05[5:4] and then change the watchdog to new timer values. This ensures the watchdog
timer is restarted after new value is written.
POR
watchdog timer expired
Reset registers
I2C interface enabled
Y
I2C Write?
N
Default Mode
Reset watchdog timer
Reset registers
Host Mode
Start watchdog timer
Host programs registers
Reset REG01
Y
bit[6]?
N
Y
N
I2C Write?
Y
Watchdog Timer
N
Expired?
Figure 18. Watchdog Timer Flow Chart
8.4.1.1 Plug in USB100mA Source with Good Battery
When the input source is detected as 100mA USB host, and the battery voltage is above batgood threshold
(V_BATGD), the charger device enters HIZ state to meet the battery charging spec requirement.
If the charger device is in host mode, it will stay in HIZ state even after the USB100mA source is removed, and
the adapter plugs in. During the HIZ state, REG00[7] is set HIGH and the system load is supplied from battery. It
is recommended that the processor host always checks if the charger IC is in HIZ state when it wakes up. The
host can write REG00[7] to 0 to exit HIZ state.
If the charger is in default mode, when the DC source is removed, the charger device will get out of HIZ state
automatically. When the input source plugs in again, the charger IC runs detection on the input source and
update the input current limit.
8.4.1.2 USB Timer When Charging from USB100mA Source
The total charging time in default mode from USB100mA source is limited by a 45-min max timer. At the end of
the timer, the device stops the converter and goes to HIZ.
26
Submit Documentation Feedback
Product Folder Links: bq24298
Copyright © 2015, Texas Instruments Incorporated