The BQ25751 is a wide input voltage, lead-acid switched-mode buck-boost battery charge controller with direct power path control. 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 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.

For Lead Acid battery chemistry, the device checks battery voltage and charges the battery in three different phases accordingly: constant current (CC), constant voltage absorption charging (CV), and constant voltage float charging (CV). The transition from absorb charging phase to float charging phase occurs when either the charge current is below termination current limit, or the CV timer expires. After this transition, the device remains in the float charging phase indefinitely.

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, transitions to power the system load from the battery, and the PG pin pulls HIGH. In the absence of an input source, the device can power the system load from battery through BATFET or via reverse power flow, discharging the battery through the buck converter to generate a programmable, regulated voltage on system which is above or below the battery voltage.

The charger provides various safety features for battery charging and system operation, including battery temperature negative thermistor (NTC) monitoring, 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 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/system/thermistor voltages (IAC, IBAT, VAC, VBAT, VSYS, TS).

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