BQ24188_15 Datasheet, PDF (20/52 Pages) Texas Instruments – bq24188 2A, 30V, Host-Controlled Single-Input, Single Cell Switchmode Li-Ion Battery Charger with Power Path Management and USB-OTG Support

bq24188
SLUSC44A – DECEMBER 2014 – REVISED MAY 2015
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Device Functional Modes (continued)
9.4.9 Battery Discharge FET (BGATE)
The bq24188 contains a MOSFET driver to drive an external discharge FET between the battery and the system
output. This external FET provides a low impedance path for supplying the system from the battery. Connect
BGATE to the gate of the external discharge P-channel MOSFET. BGATE is on (low) under the following
conditions:
1. No input supply connected.
2. HZ_MODE = 1
3. CD terminal = 1
9.4.10 DEFAULT Mode
DEFAULT mode is used when I2C communication is not available. DEFAULT mode is entered in the following
situations:
1. When the charger is enabled and V_BAT<V_BATGD before I²C communication is established
2. When the watchdog timer expires without a reset from the I²C interface
3. The RESET bit is written in the I²C register
In DEFAULT mode, the I²C registers are reset to the default values. The 2 minute safety timer is reset and starts
when DEFAULT mode is entered if a charge cycle is underway. The default value for V_BATREG is 3.6V for the
BQ24188 , and the default value for I_CHARGE is 1A. For the bq24188, the input current limit in DEFAULT mode is
set by PSEL. (See Power Source Selector Input section) DEFAULT mode is exited by writing to the I²C interface.
Note that if termination is enabled and charging has terminated, a new charge cycle is NOT initiated when
entering DEFAULT mode.
9.4.11 Good Battery Monitor
The bq24188 contains a good battery monitor circuit that places the bq24188 into high-z mode if the battery
voltage is above the V_BATGD threshold while in DEFAULT mode. This function is used to enable compliance to
the battery charging standard that prevents charging from an un-enumerated USB host while the battery is above
the good battery threshold. If the bq24188 is in HOST mode, it is assumed that USB host has been enumerated
and the good battery circuit has no effect on charging. Any write to the i2c places the bq24188 in HOST mode
and clears the high-impedance mode condition. The HZ_MODE bit is not updated during this condition.
9.4.12 Power Source Selector Input
The bq24188 contains a PSEL input that is used to program the input current limit during DEFAULT mode. Drive
PSEL high to indicate a USB source is connected to the input and program the 100mA current limit for IN. Drive
PSEL low to indicate that an AC Adapter is connected to the input. When PSEL is low, the IC starts up with a
1.5A input current limit. Once an I²C write is done and the device is in HOST mode, the PSEL has no effect on
the input current limit until the watchdog timer expires and returns the bq24188 to DEFAULT mode.
9.4.13 Safety Timer and Watchdog Timer in Charge Mode
At the beginning of charging process, the bq24188 starts the safety timer. This timer is active during the entire
charging process. If charging has not terminated before the safety timer expires, the IC enters suspend mode
where charging is disabled. When a safety timer fault occurs, a single 128μs pulse is sent on the STAT and INT
outputs and the STATx and FAULT_x bits of the status registers are updated in the I2C. The CE bit, Hi-Z mode,
or power must be toggled in order to clear the safety timer fault. The safety timer duration is selectable using the
TMR_X bits in the Safety Timer Register/ NTC Monitor register. When the safety timer is active, changing the
safety timer duration resets the safety timer. The bq24188 also contains a 2X_TIMER bit that enables the 2x
timer function to prevent premature safety timer expiration when the charge current is reduced by a load on SYS
or a NTC condition. When 2X_TIMER is enabled, the timer runs at half speed when any loop is active other than
CC or CV. This includes V_INDPM, input current limit, or thermal regulation. The timer also runs at half speed during
TS warm/cool conditions and when the LOW_CHG bit is set to '1'.
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