TP4056 Pinout, Specifications & Common Mistakes — 1A Li-Ion Charger IC (SOP-8) | ICMASS

TP4056 Pinout and Pin Functions

Key Specifications

Current programming formula: I_BAT = 1200 / R_PROG (where R_PROG is in kΩ and I_BAT is in mA). 1.2kΩ = 1000mA, 2kΩ = 580mA, 10kΩ = 130mA. The golden rule: charge at 0.5C maximum. A 500mAh cell at 250mA max. A 300mAh LiPo at 1A is a fire risk.

Typical Application Circuit

Basic charging circuit: USB 5V → TP4056 → Li-Ion battery. Two 10µF ceramic caps close to VCC and BAT. R_PROG sets charge current. CHRG LED (red) during charge, STDBY LED (green) when done. For protected modules: load to OUT+/OUT−, never B+/B−.

Load sharing modification: The TP4056 can't distinguish battery current from load current alone. Add a P-ch MOSFET (DMG3415) and Schottky diode. USB absent → MOSFET connects battery to load. USB present → load runs from USB, TP4056 charges battery independently. No termination confusion.

Common Mistakes When Using TP4056

1. Connecting load to B+/B− instead of OUT+/OUT−. B+/B− are raw battery terminals before the DW01A. Connecting load here bypasses over-discharge, over-current, and short-circuit protection entirely. If your module has OUT terminals, use them. If not, you have the unprotected variant.

2. Charging while load is active (no load sharing). The TP4056 terminates at C/10. If a load draws >C/10, the charger never sees termination and trickle-charges indefinitely. This degrades the battery. Disconnect the load during charging, or add a load-sharing circuit.

3. Charging at 1A into a small cell. Default 1.2kΩ R_PROG = 1A. A 300mAh LiPo at 1A is >3C — far above the 0.5C safe limit. The cell heats rapidly, potentially venting. Always calculate: R_PROG (kΩ) = 1200 / desired I_CHG (mA). A 500mAh cell needs R_PROG ≥ 4.8kΩ (250mA).

4. Skipping thermal vias on the exposed pad. At 5V in, 3.5V battery, 1A: dissipation = 1.5W. The exposed pad is the only heat path. Without 4–6 vias to a GND plane, the chip hits 120°C thermal regulation and silently throttles — turning your 1-hour charge into 4.

5. Using TP4056 with LiFePO4 cells. LiFePO4 terminates at 3.65V. The TP4056 charges to 4.2V. Connecting a LiFePO4 cell to a TP4056 overcharges it by 0.55V per cell, rapidly destroying it. Use a dedicated LiFePO4 charger IC (e.g., CN3058, TP5000 with LiFePO4 mode).

6. Assuming the DW01A's 2.4V cutoff protects battery health. The DW01A disconnects at ~2.4V — this is an emergency cutoff to prevent catastrophic failure, not a battery-health threshold. Regularly discharging to 2.4V dramatically shortens cycle life. Implement a firmware-level cutoff at 3.0–3.2V in your MCU for normal operation.

7. Sealed enclosure with no ventilation. At 1.5W dissipation in a sealed 50×30×20mm enclosure, the internal temperature can easily exceed 80°C. The TP4056 throttles, but the battery also cooks — Li-Ion cells degrade rapidly above 45°C. Add ventilation holes, or use a switching charger (TP5100) for enclosed designs.

Frequently Asked Questions

Q1: Why is my TP4056 only charging at ~100mA?

A: The battery is below 3.0V and in precharge (trickle) mode. The TP4056 delivers ~10% of programmed current until the battery reaches 3.0V. If your battery is deeply discharged, this can take 30–60 minutes. It's not a fault — it's protecting the cell. If the battery never rises above 3.0V, check whether your load is drawing the trickle current and preventing the battery voltage from climbing.

Q2: Can I charge and power my circuit at the same time?

A: Not without a load-sharing circuit. The TP4056 terminates when current drops to C/10. If your load draws >C/10, the charger never terminates. Add a P-channel MOSFET + Schottky diode load-sharing circuit, or physically disconnect the load during charging.

Q3: Should I buy the protected or unprotected module?

A: Protected (DW01A + 8205A), almost always. The protected variant adds over-charge, over-discharge, over-current, and short-circuit protection for about $0.20 more. The only time you'd use unprotected is when your system already has a dedicated BMS or fuel gauge IC handling protection, or when the module must be as small as possible.

Q4: Why does my TP4056 get so hot?

A: Linear regulation = heat. At 5V input and 3.5V battery at 1A, dissipation is (5 − 3.5) × 1 = 1.5W. Solutions: reduce charge current (increase R_PROG), improve PCB thermal design (vias under exposed pad), or switch to a switching charger (TP5100) for lower heat.

Q5: Can I use TP4056 for multiple cells in series?

A: Only with isolated power supplies per cell. Each TP4056 needs its own galvanically isolated 5V supply. Connecting multiple TP4056 modules to the same USB supply with cells in series creates a short circuit through the shared ground. For multi-cell packs, use a dedicated multi-cell BMS with balance charging.

Q6: The charge LED never turns off. What's wrong?

A: Either the battery never reaches 4.2V (damaged cell), or a load is drawing current preventing C/10 termination, or the input voltage is below 4.2V keeping the charger in CC mode permanently. Disconnect the load. If the LED still never turns off, test the battery voltage — a healthy cell should reach 4.15–4.20V within a few hours.