USB-C charging: the power path
Follow the energy from a USB-C charger into a TP4056 and a Li-ion cell. The TP4056 is a linear charger: the difference between the 5 V input and the cell voltage, times the charge current, becomes heat in the chip. Switch on Tools → Power path to watch it.
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How it works
USB in: P = V_in × I = 0 V × 0 A = 0 W
Into the cell: 0 V × 0 A = 0 W
Heat in the TP4056: (V_in − V_cell) × I = 0 W, so the charger is 0 % efficient. A buck charger IC would waste far less, which matters for fast charging.
Try it on the bench
- Turn on Tools → Power path: USB in, into the cell and out to the load, with the heat shown at the chip.
- Select the TP4056 and press 🧊 Inspect in 3D: the TP4056 IC glows hottest.
- Set the TP4056’s Rd to missing: the USB-C charger never turns VBUS on, so nothing charges.
Parts on the bench
In the course
Zen’s Electronics Design Mastery, module “Capstone — Connected Tracker”.