BQ25601 Charge Control IC

The BQ25601 sits at the center of the charging circuit in millions of single-cell Li-Ion and Li-Polymer smartphones. It combines switch-mode battery charging with narrow VDC (NVDC) power path management on one die, so the phone can charge the battery and run the system simultaneously without dropping power when the battery is deeply discharged or completely removed. For a technician, that instant-on behavior is what lets a phone power up even before the battery reaches a safe voltage — a detail that matters directly when you're chasing a dead-after-charge fault.Inside, the chip runs a 1.5MHz synchronous buck converter that reaches 92% charge efficiency at 2A from a 5V USB input. It auto-detects the input source type — standard USB SDP, DCP, or a non-standard high-voltage adapter — and adjusts the input current limit accordingly, from 100mA up to 3.2A in 100mA steps. Input voltage support runs from 3.9V to 13.5V, with a 22V absolute maximum rating, so the IC survives voltage spikes from bad chargers or damaged input paths that would otherwise take out a lower-rated charger IC.Charging itself happens in three phases — pre-conditioning, constant current, and constant voltage — without needing software control to start the cycle. The chip terminates charging automatically once current drops below the preset limit and battery voltage clears the recharge threshold, then restarts the cycle if the battery drops back below that threshold. Charge voltage regulation holds ±0.5% accuracy across the 3.85V to 4.62V range, and current regulation stays within ±5% at 1.5A — tight enough that board-level charging faults you diagnose almost always trace back to a component around the IC, not the regulation itself.USB OTG support is built in through a boost converter that supplies 5.15V on VBUS with a constant current limit up to 1.2A and 92% efficiency at 1A output. Soft-start handles capacitive loads up to 500µF, and output short-circuit protection shuts the boost path down cleanly if something downstream faults. If a phone on your bench powers external USB devices intermittently or not at all, this is the block responsible.Thermal protection layers in at two stages. Thermal regulation kicks in at a programmable 110°C junction temperature and throttles charge current down — during this state the safety timer runs at half rate and termination disables, so charging behaves differently than a normal cycle. Full thermal shutdown triggers at 160°C IC surface temperature, cutting the converter and BATFET, and recovers automatically once the chip cools 30°C below that point. Combined with input UVLO, input overvoltage protection, and NTC-based battery temperature monitoring, these features are usually what's protecting a board from a swollen or shorted battery rather than letting damage propagate.The BATFET includes ship mode, wake-up, and full system reset control through the QON pin — the same mechanism behind a phone that won't power on until you force a battery disconnect sequence through this IC. All switching FETs, current sensing, and loop compensation sit inside the package, along with a 19.5mΩ battery discharge MOSFET for efficient supplement-mode discharge when the input source can't meet system load alone.On the repair bench, board rework on the BQ25601 usually comes up for charging issue, no charging, or slow charging complaints, and occasionally for hang on logo faults tied to a bad power path rather than software. IC change karna on this part calls for a hot air station with tight temperature control given the 24-pin WQFN's fine 4mm × 4mm footprint, along with flux and paste suited to QFN reballing. Confirm continuity and shorts on VBUS, SYS, and BAT pins before reflow — a shorted output downstream will damage a fresh IC the same way it damaged the original.