Li-ion Batteries Got a New Charging Module TP5100

Original Hackster article: https://www.hackster.io/sainisagar7294/li-ion-batteries-got-a-new-charging-module-d04a46

TP5100-based dual-cell Li-ion charging module

I am building a portable lab bench power supply that needs two Li-ion cells in series (8.4V total). The problem: standard TP4056 modules only handle a single 4.2V cell. I needed something that could charge both 4.2V single and 8.4V dual packs from a 12V adapter. That is where the TP5100 comes in a switching-mode charger with a single pin to select between 1S and 2S operation.

TP5100 Overview

The TP5100 is a step-down switching charger running at 400kHz. It accepts 5V–18V input and delivers up to 2A of programmable charging current via an external sense resistor. All protection is built in: input overcurrent, undervoltage, over-temperature, short circuit, and reverse battery.

Key specs:
• Input: 5V–18V (covers 12V adapters)
• Max charging current: 2A (programmable)
• Switching frequency: 400kHz
• Cell configuration: 1S (4.2V) or 2S (8.4V) via onboard solder pad

Charging Phases

The IC steps through three phases automatically:

1. Trickle: if the battery is over-discharged below 2.8V, charges at 1/10th of max current until it recovers.
2. Constant current: charges at the set max current until voltage nears the target.
3. Constant voltage: holds at 4.2V (or 8.4V); current tapers to ~0.07C, then terminates.

Two onboard LEDs show live charge status.

Circuit with 1S/2S selection and sense resistor

Compact PCB with separated input/output sections

Testing

Important: this module does not support balance charging. For 2S packs, use identical cells from the same batch and manufacturer so initial capacities are matched.

Results 1S cell pre-charged at 4.1V: ~300mA (CV taper phase). 2S pack: ~500mA. Both are expected since cells were near full. All protection features tested and working.