Texas Instruments‘ battery charger IC BQ25798 is a fully integrated switch-mode buck-boost charger for 1-4 cell Li-Ion and Li-polymer batteries. The integration includes 4 switching MOSFETs, input and charge current sense circuits, battery FETs, and all loop compensation for the buck-boost converter. It uses NVDC power path management to regulate the system no lower than a configurable minimum system voltage. When the system power exceeds the input source rating, the battery supplement mode supports the system without overloading the input source. The BQ25798 also maximizes PV panel power using its built-in V OC scaling MPPT algorithm. The BQ25798 supports ultra-fast switching from the adapter to the converted battery voltage in standby mode.

The charger supports narrow VDC power path management, in which the system is regulated at a voltage slightly above the battery voltage and is not allowed to drop below the minimum system voltage. The minimum system voltage allows the system to operate even if the battery is fully discharged or removed. When the system power exceeds the input source rating, the battery supplement mode supports the system power requirement without overloading the input source.

The device can charge the battery from a variety of input sources, including traditional USB adapters, high voltage USB PD adapters, and traditional barrel adapters. The charger automatically sets the converter into a buck, boost, or buck-boost configuration based on the input voltage and battery voltage, without host control. Dual input source selectors manage power from two different input sources. Input selection is controlled by the host via I2C, with default source #1 (VAC1) as the primary input and source #2 (VAC2) as the auxiliary input.

To support fast charging using an adjustable high voltage adapter, the device provides D+/D- handshaking. The device is compliant with the USB 2.0 and USB 3.0 power delivery specifications and features input current and voltage regulation. Additionally, the Input Current Optimizer (ICO) allows detection of the maximum power point of an unknown input source. The BQ25798 also provides a Maximum Power Point Tracking (MPPT) algorithm to optimize power consumption when connected to a solar cell.

In addition to the charging mode controlled by the I 2 C host, this charger also supports an autonomous charging mode. After power-up, charging is enabled using the default register settings. The device can complete a charge cycle without any software involvement. It detects the battery voltage and charges the battery in different stages: trickle charge, precharge, constant current (CC) charge and constant voltage (CV) charge. At the end of the charging cycle, the charger automatically terminates when the charging current falls below the preset limit (termination current) of the constant voltage stage. When a fully charged battery falls below the charge threshold, the charger will automatically begin another charge cycle.

In the absence of an input source, the device supports USB On-the-Go (OTG) functionality that discharges the battery to produce an adjustable 2.8-V to 22-V voltage on VBUS in 10-mV steps, conforming to The USB PD 3.0 specification defines the Programmable Power Supply (PPS) function. The BQ25798 also provides a backup mode to use the adjustable OTG voltage to power the system load on the PMID when the adapter is removed.

The charger provides various safety features for battery charging and system operation, including battery temperature negative thermistor monitoring, trickle charging, pre-charge and fast-charge timers, and overvoltage/overcurrent protection for battery and input. Thermal regulation reduces charge current when the junction temperature exceeds a programmable threshold. The device‘s STAT output reports charging status and any fault conditions. The PG output indicates whether a good power source is present. In the event of a fault, the INT pin notifies the host immediately.

Texas Instruments‘ battery charger IC, the BQ25798, is available in a 29-pin 4mm x 4mm QFN package.