BQ24297 Datasheet, PDF (31/48 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

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SLUSBP6A – SEPTEMBER 2013 – REVISED OCTOBER 2013
RT1 = 5.52 kΩ
RT2 = 31.23 kΩ
Charging Termination
The device terminates a charge cycle when the battery voltage is above recharge threshold, and the current is
below termination current. After the charging cycle is complete, the BATFET turns off. The converter keeps
running to power the system, and BATFET can turn back on to engage supplement mode.
When termination occurs, the status register REG08[5:4] is 11, and an INT is asserted to the host. Termination is
temporarily disabled if the charger device is in input current/voltage regulation or thermal regulation. Termination
can be disabled by writing 0 to REG05[7].
Termination when REG02[0] = 1
When REG02[0] is HIGH to reduce the charging current by 80%, the charging current could be less than the
termination current. The charger device termination function should be disabled. When the battery is charged to
fully capacity, the host disables charging through CE pin or REG01[5:4].
Charging Safety Timer
The device has safety timer to prevent extended charging cycle due to abnormal battery conditions. The safety
timer is 4 hours when the battery is below batlowv threshold. The user can program fast charge safety timer
(default 12 hours)through I2C (REG05[2:1]). When safety timer expires, the fault register REG09[5:4] goes 11
and an INT is asserted to the host. The safety timer feature can be disabled via I2C (REG05[3]).
The following actions restart the safety timer after safety timer expires:
• Toggle the CE pin HIGH to LOW to HIGH (charge enable)
• Write REG01[5:4] from 00 to 01 (charge enable)
• Write REG05[3] from 0 to 1 (safety timer enable)
During input voltage/current regulation, thermal regulation, or FORCE_20PCT bit (REG02[0]) is set , the safety
timer counting at half clock rate since the actual charge current is likely to be below the register setting. For
example, if the charger is in input current regulation (IINDPM) throughout the whole charging cycle, and the
safety time is set to 5 hours, the safety timer will expire in 10 hours. This feature can be disabled by writing 0 to
REG07[6].
Safety Timer Configuration Change
When safety timer value needs to be changed, it is recommended that the timer is disabled first before new
configuration is written to REG05[2:1]. The safety timer can be disable by writing 1 to REG05[3]. This ensures
the safety timer restart counting after new value is configured.
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.
Host Mode and Default Mode
The device is a host controlled device, but it can operate in default mode without host management. In default
mode, the device can be used as an autonomous charger with no host or with host in sleep.
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.
Copyright © 2013, Texas Instruments Incorporated
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