BQ25638

The BQ25638 is a highly-integrated 5A switch-mode battery charge management and system power path management device for single cell Li-Ion and Li-polymer batteries. The design is highly integrated with built-in current sensing, loop compensation, input reverse-blocking FET (RBFET, Q1), high-side switching FET (HSFET, Q2), low-side switching FET (LSFET, Q3), and battery FET (BATFET, Q4) between system and battery. The device uses NVDC power path management, regulating the system slightly above the battery voltage without dropping below a configurable minimum system voltage. The low impedance power path optimizes switch-mode operation efficiency, reduces battery charging time and extends battery life during discharging phase. The I2C serial interface with charging and system settings makes BQ25638 a truly flexible design.

The device supports a wide range of input sources, including standard USB host port, USB charging port, and USB compliant high voltage adapter. The device is compliant with USB 2.0 and USB 3.0 power specifications for input current and voltage regulation. In addition, the Input Current Optimizer (ICO) supports the detection of maximum power point of the input source without overload. BQ25638 has an ILIM pin to set the default input current limit and a TS_BIAS pin for controlled thermistor bias. The device also meets USB On-the-Go (OTG) operation power rating specifications with constant current limit up to 3.2A.

The power path management regulates the system slightly above battery voltage but does not drop below the programmable minimum system voltage. With this feature, the system maintains operation even when the battery is completely depleted or removed. When the input current limit or input voltage limit is reached, the power path management automatically reduces the charge current. If the system load continues to increase, the power path discharges the battery until the system power requirement is met. This supplement mode prevents overloading the input source.

The device initiates and completes a charging cycle without host control. By sensing the battery voltage, the device charges the battery in four different phases: trickle charge, pre-charge, constant current (CC) charge and constant voltage (CV) charge. At the end of the charging cycle, the charger automatically terminates when the charge current is below a preset threshold and the battery voltage is higher than the recharge threshold. Termination is supported for TS pin COOL, PRECOOL, NORMAL, WARM and PREWARM temperature zones. When the full battery voltage falls below the programmable recharge threshold, the charger automatically starts a new charging cycle.

The charger provides various safety features for battery charging and system operations, including battery negative temperature coefficient (NTC) thermistor monitoring, charging safety timer and overvoltage and overcurrent protections. The thermal regulation reduces charge current when the junction temperature exceeds the programmable threshold. The STAT output reports the charging status and any fault conditions. Other safety features include battery temperature sensing for charge mode and OTG boost mode, thermal shutdown and input UVLO and over-voltage protection. The PG output indicates if a good power source is present and above the programmable PG_TH value. The INT output immediately notifies the host when a fault occurs or status changes.

The device also provides a 12-bit analog-to-digital converter (ADC) for monitoring charge current and input/battery/system (VBUS, BAT, SYS, TS) voltages. In addition, the ADCIN pin can be used to monitor an external signal up-to 1V. The QON pin provides BATFET enable and reset control to exit ultra-low power mode or initiate a full system reset.

BQ25638 is available in a 30-ball, 2.07mm × 2.36mm DSBGA package.