The BQ25756 is a wide input voltage, Li-Ion, Li-polymer, LiFePO₄ bi-directional switched-mode buck-boost battery charge controller. The device offers high-efficiency battery charging over a wide voltage range with accurate and programmable charge current and charge voltage regulation, in addition to automatic charge preconditioning, termination, and charge status indication. The device integrates all the loop compensation and 5-V gate drivers for the buck-boost converter, thereby providing a high density solution with ease of use. The switching frequency of the device can be programmed or forced to follow an external clock frequency via the FSW_SYNC pin. While switching under light-load the device offers an optional Pulse Frequency Modulation (PFM) mode to increase efficiency. The charger has a digital state machine that advances the charger's states as the converter analog feedback loops hand off control to each other. It also manages the fault protection comparators. The loops regulate and comparators compare against reference values in the I²C registers, unless clamped by external resistors.

Besides the I²C host-controlled charging mode, the device also supports autonomous charging mode via resistor programmable limits. Input current, charge current and charge voltage regulation targets can be changed via the ILIM_HIZ, ICHG, and FB pins, respectively. The device can complete a charging cycle without any software intervention. Charging function is controlled via the CE pin.

For Li-Ion and LiFePO₄ chemistries, the device checks battery voltage and charges the battery in different phases accordingly: trickle charging, pre-charging, constant current (CC) charging and constant voltage (CV) charging. At the end of the charging cycle, the charger automatically terminates when the charge current is below the termination current limit in the constant voltage phase. When the full battery falls below the recharge threshold, the charger automatically starts a new charge cycle.

The input operating window is programmed via the ACUV and ACOV pins. When the input voltage is outside the programmed window, the device automatically stops the charger, and the PG pin pulls HIGH.

The charger provides various safety features for battery charging and system operation, including battery temperature negative thermistor (NTC) monitoring, charge timers and over-voltage/over-current protections on battery and input. The thermal shutdown prevents charging when the junction temperature exceeds the T_SHUT limit.

The device supports buck-boost reverse power direction to deliver power from the battery to the input when the adapter is not present. In reverse mode, the regulation voltage and current can be programmed via the I²C interface (VAC_REV and IAC_REV) to provide a CC/CV profile supporting the USB-PD Extended Power Range (EPR).

The device has three status pins (STAT1, STAT2, and PG) to indicate the charging status and input voltage status. These pins can be used to drive LEDs or communicate with a host processor. If needed, these pins can also be used as general purpose indicators and their status controlled directly by the I²C interface. In addition, the CE pin can also be used as a general purpose indicator. The INT pin immediately notifies host when the device status changes, including faults.

The device also provides a 16-bit analog-to-digital converter (ADC) for monitoring input current, charge current and input/battery/thermistor voltages (IAC, IBAT, VAC, VBAT, TS).

The device comes with a 36-pin 5-mm × 6-mm QFN package with 0.5-mm pin pitch.