USB-C Li-ion charger board

Low voltage · safe

Single-cell charge and protection board · Level 2 / 5

Educational content · Awaiting expert review.

USB-C Li-ion charger board
  1. J1 · USB-C socket
  2. R4 · CC1 resistor
  3. R5 · CC2 resistor
  4. TP1 · IN+ hole
  5. TP2 · IN- hole
Stop 1 / 8 · USB input

USB-C input

In short
Charge power enters the board here: through the USB-C socket or the IN+ and IN- holes.
Analogy
Like an ID card: over a cable with USB-C at both ends, two small resistors tell the connected charger "I’m a device that takes power"; only then does such a charger supply power. A cable with a USB-A end supplies power without checking this ID.
Where to look
The silver USB-C socket on the left and the two small resistors right next to it (R4, R5).
Measure · De-energized measurement · Continuity

First disconnect the USB cable, the cell and the circuit at the output. Set the multimeter to continuity mode. Touch the red probe to the VBUS terminal (A9) of the USB socket and the black probe to the IN+ hole (TP1). If you hear a beep, the input path is intact.

Expected display: 0.0 Ωbeep heard

J1:A9 ↔ TP1:1

You expect continuity along the same VBUS line; a broken line shows an open circuit.

More
What it does
Carries the USB supply to the charging circuit; the CC resistors announce the power sink role.
How to recognize it
The metal socket on the left and the R4/R5 beside it.
Why here
Makes the source recognize the board as a power sink.
If it fails
If the socket or input path breaks, the board gets no power.