BQ24296_15 Datasheet, PDF (16/55 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 Feature Description
9.3.1 Device Power Up
9.3.1.1 Power-On-Reset (POR)
The internal bias circuits are powered from the higher voltage of VBUS and BAT. When VBUS or VBAT rises
above UVLOZ, the sleep comparator, battery depletion comparator and BATFET driver are active. I²C interface
is ready for communication and all the registers are reset to default value. The host can access all the registers
after POR.
9.3.1.2 Power Up from Battery without DC Source
If only battery is present and the voltage is above depletion threshold (V_{BAT_DEPL}), the BATFET turns on and
connects battery to system. The REGN LDO stays off to minimize the quiescent current. The low R_DSON in
BATFET and the low quiescent current on BAT minimize the conduction loss and maximize the battery run time.
During both boost and charge mode, the device always monitors the discharge current through BATFET. When
the system is overloaded or shorted, the device will immediately turn off BATFET and keep BATFET off until the
input source plugs in again.
9.3.1.2.1 BATFET Turn Off
The BATFET can be forced off by the host through I²C REG07[5]. This bit allows the user to independently turn
off the BATFET when the battery condition becomes abnormal during charging. When BATFET is off, there is no
path to charge or discharge the battery. When battery is not attached, the BATFET should be turned off by
setting REG07[5] to 1 to disable charging and supplement mode.
9.3.1.2.2 Shipping Mode
To extend battery life and minimize power when system is powered off during system idle, shipping, or storage,
the device can turn off BATFET so that the system voltage is zero to minimize the leakage. The BATFET can be
turned off by setting REG07[5] (BATFET_DISABLE) bit.
In order to keep BATFET off during shipping mode, the host has to disable the watchdog timer (REG05[5:4] =
00) and disable BATFET (REG07[5] = 1) at the same time. Once the BATFET is disabled, one of the following
events can turn on BATFET and clear REG07[5] (BATFET_DISABLE) bit.
1. Plug in adapter
2. Write REG07[5] = 0
3. watchdog timer expiration
4. Register reset (REG01[7] = 1)
5. A logic low to high transition on QON pin (refer to Figure 11 for detail timing)
QON
Min. 2ms
BATFET Status
Turn off by i2c command
REG07[5]=1
Turn on by QON
REG07[5]=0
Figure 11. QON Timing
9.3.1.3 Power Up from DC Source
When the DC source plugs in, the charger device checks the input source voltage to turn on REGN LDO and all
the bias circuits. It also checks the input current limit before starts the buck converter.
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