Batt Charger
A battery-charger IC controls the current and voltage applied to a rechargeable cell through the standard CC/CV charge profile, monitors cell temperature via a thermistor, and terminates charge when the cell is full. It may also protect against short-circuit and over-voltage.
An internal current-sense amplifier regulates a MOSFET pass element or switching converter to deliver constant current until the cell voltage reaches the termination threshold. Once the threshold is hit, the control loop switches to constant-voltage mode; when charge current tapers below a programmed fraction of the initial rate, the IC signals charge complete.
In plain terms
A careful nurse topping up a patient's IV: first it flows at a fixed rate (constant current), then as the bag fills it slows to a trickle to keep pressure steady (constant voltage) without overfilling.
Why designers use it
- Charge single-cell or multi-cell lithium-ion/polymer packs safely.
- Implement solar MPPT charging without extra ICs.
- Manage multi-chemistry packs (LiFePO₄, NiMH) with configurable profiles.
- Provide USB-C PD-aware charging in portable devices.
Best for
- Li-ion / LiPo single-cell
- USB charging
- Solar input
Key specifications
- Cell chemistry: Li-ion, LiFePO₄, NiMH, Pb-acid
- Vfloat: 3.6 V (LFP) – 4.4 V (Li-Co)
- Charge current: 100 mA – 6 A
- Termination: C/10, C/20, or timer
- Thermal monitor: JEITA spec for Li-ion
When not to use it
- When the charging source is a non-isolated wall adapter and isolation is required by safety standards — use a charger with isolated flyback topology.
- For lead-acid batteries with float-charge requirements — lithium ICs terminate charge instead of floating.
Common mistakes
- Connecting the battery without a series fuse — a shorted pack can draw hundreds of amps through the charger.
- Forgetting the NTC thermistor — the IC disables charging if the thermistor pin is open or out of range, and beginners mistake this for a fault.
- Setting the charge current above the cell's 1C rate, causing rapid capacity degradation.
Where you will find it
- A portable Bluetooth speaker uses an MCP73831 charger IC to top up its 2000 mAh LiPo from a USB-A port: the IC limits charge current to 500 mA (matching USB spec), terminates when the cell hits 4.2 V, and drives an LED to signal completion — all with no microcontroller firmware needed.
- An electric toothbrush uses a wireless Qi receiver feeding a linear battery charger IC: the charger accepts the rectified inductive power, limits current to the small NiMH cell's 0.1C safe rate, and stops charging once the cell terminal voltage indicates full charge, preventing the cell from overheating in its sealed handle.
- A trail camera uses a solar-panel-input charger IC with MPPT: the IC adjusts its input impedance to track the panel's peak-power point as cloud cover varies, extracting maximum energy into the pack so the camera stays powered through weeks of overcast weather without a mains connection.
A short history
A battery charger delivers controlled current and voltage to restore a rechargeable cell's stored energy. Many fast-charging circuits hold current constant while monitoring voltage, and sometimes temperature, to judge the battery's state and end charging, since overcharging can reduce battery life, cause overheating, or release gases. Slow chargers are simpler, but fast-charging designs must suit the battery chemistry for reliable charging and termination.
Good to know
- Lithium-ion charging follows constant-current then constant-voltage (CC-CV); the transition voltage controls capacity vs lifetime — drop from 4.2 V to 4.1 V and cycle life roughly doubles.
- JEITA Li-ion specifications adjust charge current and termination voltage based on cell temperature; below 0 °C charging is forbidden, above 45 °C it's reduced.
- USB-PD chargers negotiate up to 240 W (48 V × 5 A) — the same chip family also handles a 100 mA wearable battery; modern chargers are wildly programmable.