Choosing the right battery charger IC determines the safety, efficiency, and longevity of your lithium battery charging circuit. The CN3065, MCP73831, and BQ24074 represent three of the most popular single-cell Li-ion/LiPo charger ICs used by Indian hobbyists and product designers. Each has distinct strengths: the CN3065 excels at solar charging, the MCP73831 is the simplest and smallest, and the BQ24074 offers advanced power path management. This guide compares all three with practical circuit advice.
Popular Battery Charger ICs Overview
All three ICs implement CC/CV (constant current/constant voltage) charging, the standard algorithm for lithium-ion and lithium-polymer cells. The charging process:
- Pre-charge: If cell voltage is below ~3.0V, charge at reduced current (typically 10% of full rate) to safely bring the cell up
- CC phase: Charge at programmed constant current until cell reaches 4.2V
- CV phase: Hold voltage at 4.2V while current tapers down
- Termination: When current drops below threshold (typically 10% of CC rate), charging stops
The ICs differ in input voltage range, maximum charge current, features, and package size. All three are available on breakout modules from Indian suppliers for under ₹100 each.
CN3065: Solar-Ready Li-Ion Charger
The CN3065 from Consonance Semiconductor is specifically designed for solar panel and USB dual-input charging. It is the go-to choice for outdoor IoT and solar-powered projects in India.
Key specifications:
- Input voltage: 4.4V to 6.0V (ideal for 5V solar panels and USB)
- Charge current: Programmable up to 500mA via resistor
- Charge accuracy: +/-1.5% on 4.2V termination voltage
- Package: SOP-8 (easy to hand-solder)
- Features: Automatic recharge, soft-start, thermal regulation
- Cost: ₹15-25 per IC, ₹50-80 for breakout module
Solar charging advantage: The CN3065 includes dynamic current adjustment based on available input power. When a solar panel’s output drops (cloud cover), the IC automatically reduces charge current to prevent the panel voltage from collapsing. This MPPT-like behaviour (not true MPPT, but close) maximises solar energy harvesting.
CN3065 Basic Solar Charger Circuit:
Solar panel (5V, 1W+) → VIN
ISET resistor: R = 1500 / I_charge(mA)
For 300mA: R = 1500/300 = 5kohm
For 500mA: R = 1500/500 = 3kohm
Battery → BAT pin
DONE pin → LED (charge complete indicator)
CHRG pin → LED (charging indicator)MCP73831: Compact Single-Cell Charger
The MCP73831 from Microchip is the world’s most popular single-cell Li-ion/LiPo charger IC, found in countless consumer products from Bluetooth earphones to smartwatches.
Key specifications:
- Input voltage: 3.75V to 6.0V
- Charge current: Programmable up to 500mA (MCP73831) or 1A (MCP73832)
- Charge accuracy: +/-0.75% on 4.2V (best in class)
- Package: SOT-23-5 (tiny — 3mm x 3mm)
- Quiescent current: 55 microamps (excellent for battery-powered standby)
- Features: Programmable termination current, thermal shutdown
- Cost: ₹20-40 per IC, ₹40-70 for breakout module
Why it is so popular: The MCP73831 requires only 4 external components (2 capacitors, 1 resistor, 1 LED). The circuit fits in under 1 cm2 of PCB space. Charge voltage accuracy of +/-0.75% is critical for battery longevity — every 50mV above 4.2V reduces cycle life by 10-20%.
MCP73831 Minimal Circuit:
VIN → 4.7uF capacitor to GND
PROG pin → R to GND (sets charge current)
R = 1000V / I_charge(mA)
For 500mA: R = 2kohm
For 100mA: R = 10kohm
BAT → Battery (+), 4.7uF capacitor to GND
STAT pin → LED + resistor to VIN (active low)BQ24074: Power Path with USB and Solar
The BQ24074 from Texas Instruments is the premium choice for projects requiring simultaneous charging and system operation — the “power path” feature that consumer electronics rely on.
Key specifications:
- Input voltage: 4.35V to 6.4V
- Charge current: Programmable up to 1.5A
- System output: Regulated from input OR battery automatically
- Package: QFN-20 (requires reflow soldering)
- Features: Dynamic power path management, input current limit, thermal regulation, charge status outputs
- Cost: ₹80-150 per IC, ₹150-300 for module
Power path explained: Without power path management, connecting a charger to a battery-powered device forces all current through the battery — charging it while simultaneously discharging it for the system load. This stresses the battery and creates confusing charge termination behaviour. The BQ24074 routes input power directly to the system while separately charging the battery, and seamlessly switches to battery power when input is removed.
BQ24074 Power Path Behaviour:
USB connected:
→ System powered from USB (up to 1.5A)
→ Remaining USB current charges battery
→ Battery acts as backup only
USB disconnected:
→ System powered from battery
→ Seamless switchover, no brownout
Battery full + USB connected:
→ System powered from USB
→ Battery on standby (no trickle charge)IC Comparison Table
| Feature | CN3065 | MCP73831 | BQ24074 |
|---|---|---|---|
| Max charge current | 500mA | 500mA | 1.5A |
| Power path | No | No | Yes |
| Solar optimised | Yes | No | Partially |
| External components | 5-6 | 4 | 8-10 |
| Package | SOP-8 | SOT-23-5 | QFN-20 |
| Cost (module) | ₹50-80 | ₹40-70 | ₹150-300 |
| Best for | Solar IoT | Simple USB charging | Products, power banks |
Circuit Design Tips for Indian Conditions
- Thermal derating: In Indian summer (40-45degC ambient), reduce maximum charge current by 20-30%. All three ICs have thermal regulation, but running at the edge reduces IC lifespan.
- Input decoupling: Use low-ESR ceramic capacitors (MLCC) for input and output filtering. Electrolytic capacitors degrade faster in Indian heat.
- Solar panel sizing: For CN3065 at 500mA charge, use a panel rated at least 3W (5V/600mA). Indian solar irradiance varies widely — size for 4 peak sun hours minimum.
- Reverse polarity protection: Add a Schottky diode (SS34, SS54) on the solar input. Field-deployed solar panels in India are frequently disconnected and reconnected, risking reverse connection.
- Humidity protection: Conformally coat the PCB with silicone conformal coating for outdoor deployments in coastal or monsoon-prone areas.
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Frequently Asked Questions
Can I use the TP4056 module as a substitute for these ICs?
The TP4056 module (available at Zbotic for under ₹50) is based on a similar CC/CV charger IC and works excellently for simple single-cell charging. It charges at up to 1A from USB. For most hobbyist projects in India, the TP4056 module is the fastest path from idea to working prototype. Move to CN3065/MCP73831/BQ24074 when you need solar input, power path, or custom PCB integration.
Can these ICs charge LiFePO4 cells?
Not directly. All three are designed for 4.2V termination (standard Li-ion/LiPo). LiFePO4 requires 3.6V termination. Some ICs in the same families offer LiFePO4 variants (MCP73123 for 3.6V), but the specific ICs covered here are for standard lithium only.
How do I monitor charge status in my Arduino project?
All three ICs provide status output pins (STAT/DONE/CHRG) that are open-drain outputs. Connect to an Arduino digital pin with a 10K pull-up resistor. Read LOW = charging, HIGH = done (exact logic varies by IC). This enables your firmware to display battery status on an OLED screen or transmit it via WiFi.
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