cn291short
CN291is a common, low-cost linear single-cell lithium-ion (Li-ion) battery charger IC.
Here's a quick overview of its key characteristics:
Core Features
- Charging Current:Fixed at 500mA(typical). It uses an external resistor to set this.
- Input Voltage (VCC):4.5V to 6.0V (ideal from a 5V USB or adapter).
- Charging Method:Linear constant-current (CC) / constant-voltage (CV).
- Battery Full Voltage:Pre-set to 4.2V, suitable for standard Li-ion/Li-Po cells.
- Automatic Termination:Stops charging when current drops to ~10% of the set value in the CV phase.
- Trickle Charging:Automatically charges deeply depleted batteries (< ~2.9V) with a small current before starting full CC charging.
- Status Indicators:Has two open-drain output pins for CHRG(red LED, active during charging) and STDBY(green LED, active when charge is complete/fault).
- Package:Common in SOT-23-5, making it very compact.
Typical Applications
- Low-cost consumer electronics (bluetooth speakers, toys, simple gadgets).
- USB-powered charging circuits.
- Backup battery chargers in small devices.
Advantages
- Extremely simple and cheap.Requires only 2-3 external components (resistors, LED, input/output capacitors).
- Small footprint.
- "Drop-in" solutionfor basic 5V to Li-ion charging.
Limitations / Considerations
- Linear Design:Inefficient. Dissipates excess power as heat, especially when input voltage is high and battery voltage is low. Not suitable for high-current charging or with poor thermal design.
- Fixed 500mA:Cannot be increased for faster charging.
- No Advanced Features:Lacks thermal regulation, input current limiting (except via fuse/resistor), or I²C programmability found in more advanced chargers.
In short:The CN291 is a basic, minimal-component "workhorse" charger ICfor simple, low-power, cost-sensitive applications where a 5V source is charging a standard 4.2V Li-ion cell. For higher currents, efficiency, or advanced features, a switching charger (like the CN3063 or others) would be a better choice.
