BQ24296_15 Datasheet, PDF (28/55 Pages) Texas Instruments – bq2429x I2C Controlled 3-A Single Cell USB Charger With Narrow VDC Power Path Management and Adjustable Voltage USB OTG

bq24296, bq24297
SLUSBP6B – SEPTEMBER 2013 – REVISED NOVEMBER 2014
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9.3.5.3.2 System Over-Voltage Protection (SYSOVP)
The charger device clamps the system voltage during load transient so that the components connect to system
would not be damaged due to high voltage. When SYSOVP is detected, the converter stops immediately to
clamp the overshoot.
9.3.5.4 Voltage and Current Monitoring in Boost Mode
The charger device closely monitors the VBUS voltage, as well as LSFET current to ensure safe boost mode
operation.
9.3.5.4.1 Over-Current Protection
The charger device closely monitors the RBFET (Q1) and LSFET (Q3) current to ensure safe boost mode
operation. During over-current condition, the device will operate in hiccup mode for protection. While in hiccup
mode cycle, the device turns off RBFET for t_{OTG_OCP_OFF} (32 ms typical) and turns on RBFET for t_{OTG_OCP_ON}
(260 us typical) in an attempt to restart. If the over-current condition is removed, the boost converter will maintain
the RBFET on state and the VBUS OTG output will operate normally. When over-current condition continues to
exist, the device will repeat the hiccup cycle until over-current condition is removed. When over-current condition
is detected, the fault register bit BOOST_FAULT (REG09[6]) is set high to indicate fault in boost operation. An
INT is asserted to the host.
9.3.5.4.2 VBUS Over-Voltage Protection
When an adapter plugs in during boost mode, the VBUS voltage will rise above regulation target. Once the
VBUS voltage exceeds V_{OTG_OVP}, the device stops switching and the device exits boost mode. During the over-
voltage, the fault register bit BOOST_FAULT (REG09[6]) is set high to indicate fault in boost operation. An INT is
asserted to the host.
9.3.5.5 Battery Protection
9.3.5.5.1 Battery Over-Voltage Protection (BATOVP)
The battery over-voltage limit is clamped at V_{BAT_OVP} (4% nominal) above the battery regulation voltage. When
battery over voltage occurs, the charger device immediately disables charge. The fault register REG09[3] goes
high and an INT is asserted to the host.
9.3.5.5.2 Battery Short Protection
If the battery voltage falls below V_short (2V typical), the device immediately turns off BATFET to disable the
battery charging or supplement mode. 1ms later, the BATFET turns on and charge the battery with 100-mA
current. The device does not turn on BATFET to discharge a battery that is below 2.5 V.
9.3.5.5.3 System Over-Current Protection
If the system is shorted or exceeds the over-current limit, the device latches off BATFET. DC source insertion on
VBUS is required to reset the latch-off condition and turn on BATFET.
9.4 Device Functional Modes
9.4.1 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.
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