BQ25700A Datasheet, PDF (28/82 Pages) Texas Instruments – SMBus Multi-Chemistry Battery Buck-Boost Charge Controller With System Power Monitor and Processor Hot Monitor

bq25700A
SLUSCQ8 – MAY 2017
www.ti.com
8.3.9.4 System Overvoltage Protection (SYSOVP)
When the converter starts up, the bq25700 reads CELL pin configuration and sets MaxChargeVoltage() and
SYSOVP threshold (1s – 5 V, 2s – 12 V, 3s – 18.5 V, 4s – 19.5V). Before REGx15() is written by the host, the
battery configuration will change with CELL pin voltage. When SYSOVP happens, the device latches off the
converter. REG20[4] is set as 1. The user can clear latch-off by either writing 0 to the SYSOVP bit or removing
and plugging in the adapter again. After latch-off is cleared, the converter starts again.
8.3.9.5 Battery Overvoltage Protection (BATOVP)
Battery over-voltage may happen when battery is removed during charging or the user plugs in a wrong battery.
The BATOVP threshold is 104% (1 s) or 102% (2 s to 4 s) of regulation voltage set in REG0x15().
8.3.9.6 Battery Short
If BAT voltage falls below SYSMIN during charging, the maximum current is limited to 384 mA.
8.3.9.7 Thermal Shutdown (TSHUT)
The WQFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junction temperatures low. As added level of protection, the charger converter turns off for self-
protection whenever the junction temperature exceeds the 155°C. The charger stays off until the junction
temperature falls below 135°C. During thermal shut down, the LDO current limit is reduced to 16 mA and REGN
LDO stays off. When the temperature falls below 135°C, charge can be resumed with soft start.
8.4 Device Functional Modes
8.4.1 Forward Mode
When input source is connected to VBUS, bq25700A is in forward mode to regulate system and charge battery.
8.4.1.1 System Voltage Regulation with Narrow VDC Architecture
The bq25700A employs Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by MinSystemVoltage(). Even with a deeply depleted battery, the system is
regulated above the minimum system voltage.
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode).
As the battery voltage rises above the minimum system voltage, BATFET is fully on when charging or in
supplement mode and the voltage difference between the system and battery is the VDS of BATFET. System
voltage is regulated 160 mV above battery voltage when BATFET is off (no charging or no supplement current).
See System Voltage Regulation for details on system voltage regulation and register programming.
8.4.1.2 Battery Charging
The bq25700A charges 1-4 cell battery in constant current (CC), and constant voltage (CV) mode. Based on
CELL_BATPREZ pin setting, the charger sets default battery voltage 4.2V/cell to ChargeVoltage(), or
REG0x15(). According to battery capacity, the host programs appropriate charge current to ChargeCurrent(), or
0x14(). When battery is full or battery is not in good condition to charge, host terminates charge by setting
0x12[0] to 1, or setting ChargeCurrent() to zero.
See Feature Description for details on register programming.
8.4.2 USB On-The-Go
The bq25700A supports USB OTG functionality to deliver power from the battery to other portable devices
through USB port (reverse mode). The OTG output voltage is compliant with USB PD specification, including 5 V,
9 V, 15 V, and 20 V (REG0x3B()). The output current regulation is compliant with USB type C specification,
including 500 mA, 1.5 A, 3 A and 5 A (REG0x3C()).
Similar to forward operation, the device switches from PWM operation to PFM operation at light load to improve
efficiency.
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