# USB-C PD 3S Li-ion charger
Charges a 3-cell (3S, 12.6 V full) Li-ion pack at 1.5 A from a USB-C Power Delivery charger. No microcontroller:
everything is set by resistors.
- **USB-C PD sink:** WCH CH224K asks the charger for 15 V (CFG1 = 56k to GND).
- **Charger:** TI BQ24610, a standalone synchronous buck CC/CV charger, wired as the datasheet's simplified circuit
(SLUS892D section 10.2.2: no power path, no input-current DPM).
- **Board:** 56 x 40 mm, 2 layers, GND pour on the bottom, 0.8 mm power traces, 4 M3 mounting holes.
## Settings
| What | Value | How |
| --- | --- | --- |
| Charge voltage | 12.6 V (3 x 4.2 V) | VFB = 2.1 V: 2.1 V x (1 + 500k / 100k) |
| Charge current | 1.5 A | V(ISET1) / (20 x 10 mOhm); ISET1 = 3.3 V x 10k / 110k = 0.3 V |
| Precharge / termination | ~150 mA | 1 A/V x V(ISET2); ISET2 = 3.3 V x 4.7k / 104.7k |
| Safety timer | ~5 h | TTC = 56 nF |
| Output filter | 6.8 uH + 20 uF | 13.6 kHz resonance (datasheet asks for 12-17 kHz) |
Change R9 (ISET1 divider) for a different charge current, or R3 (CFG1) for a different PD voltage.
## Status LEDs
- Red (D3, STAT1): charging
- Green (D4, STAT2): charge done
- Green (D5, PG): input power good
## Important
- **The pack must have its own 3S protection/balance board (BMS).** This charger regulates the whole pack, not each cell.
- The TS pin is held at 50% of VREF by a fixed divider, so there is no pack temperature sensing. Add an NTC divider
(see the datasheet's TS section) if the pack has a thermistor.
- A plain 5 V USB-C supply can't charge a 3S pack with this buck charger. Use a PD charger that offers 15 V.
- This is a design that passes tscircuit's checks (netlist, placement, build, shorts, PCB style). It has not been built
and tested on real hardware yet. Check the values before ordering boards.
