Charging complaints are one of the most common tickets that land on a technician's bench, and a growing share of them trace back to the buck-boost charger IC rather than the battery or the port. The BQ25790 sits at the center of that circuit in a wide range of USB-C powered devices, and understanding its role helps you separate a genuine IC fault from a connector, cable, or battery problem before you start desoldering anything. Texas Instruments designed the BQ25790 as a fully integrated switch-mode buck-boost charger for 1-4 cell Li-ion and Li-Polymer batteries. Unlike a simple linear charger, it uses four internal switching MOSFETs (Q1 through Q4) along with input and charging current sensing circuits, so it can step voltage up or down depending on what the input supply is delivering versus what the battery pack needs. That buck-boost behavior is what lets a single device charge cleanly whether you plug in a 5V phone charger or a higher-voltage PD adapter — the IC handles the conversion internally instead of relying on external regulation stages. I2C control is central to how this chip works on a real board. The BQ25790 exposes charge current, charge voltage, input current limits, and protection thresholds through I2C registers rather than fixed resistor-set values, which is why boards using this IC often show charging behavior that changes with firmware or software state, not just hardware condition. When you're chasing a charging issue on a board built around this IC, checking whether the fault clears after a software reset or full flash is worth doing before you commit to an IC change karna decision. The dual-input selector and integrated USB OTG output extend what this chip handles beyond plain charging. It can switch between two input sources, supports USB PD 3.0 negotiation directly, and includes MPPT (Maximum Power Point Tracking) logic for designs that pull power from solar or other variable-voltage sources. For rework purposes, the practical takeaway is that a failing BQ25790 can present as several different symptoms depending on which internal block is damaged — a device might still power on and boot but fail to accept charge, or it might reject fast charging and fall back to slow trickle charging over USB. Thermal regulation is built in through JEITA-profile battery temperature monitoring and IC-level thermal protection, along with input overvoltage protection (Input OVP) and input current optimization (ICO). On the bench, this matters because a board that briefly charges and then cuts out under load often points to the IC hitting a thermal or OVP threshold rather than a dead cell — a distinction that changes whether you're looking at rework or a battery swap. The BQ25790 ships in a compact 56-pin DSBGA package (2.9mm x 3.32mm), which puts it firmly in fine-pitch BGA territory. Reballing or replacing this IC calls for a hot air station with tight temperature control, a matching stencil, and a microscope for placement — standard equipment for board-level charging port repair, but not a job for a straight iron-and-flux approach given the ball pitch involved. For technicians stocking charging-circuit ICs alongside programmers, UFS tools, and hot air stations, the BQ25790 is a practical addition for any workshop handling USB-C PD devices where charging faults are a recurring hardware fault category rather than a one-off issue.
