Guides

A tiny Li-ion charger

Your first board: a TP4054 lithium charger, about the size of a postage stamp. One chip, its required components, a few routed connections, and an export. It covers every stage you’ll use on bigger boards.

1 chip2 copper layers30 × 20 mm6 stepsCovers: decoupling · charge current · netsYou’ll learn: decoupling · charge current · netsStart here

What you’re building

Charging a lithium cell safely means two phases: a controlled constant current until the cell nears 4.2 V, then a constant voltage hold while the current tapers. Getting that wrong ruins cells, so the standard approach is a charger IC with the sequence built in. The TP4054 is a common small one: five pins, no external transistors, one resistor to set the charge current.

You place that one chip and PCB Canvas offers the components it requires, placed and bound to the right pins. Every number and screenshot below comes from a run of these steps on the beta. The run took about five minutes end to end.

Steps

  1. New board

    Boards ▸ New Board ▸ width 30 ▸ height 20 ▸ Create.

    Why these numbers: 30 × 20 mm gives one chip and its companions room to route. Two copper layers, the default, puts traces on top and leaves the bottom free for crossings and a ground pour later. More layers help on dense boards; this one doesn’t need them.
  2. Add the charger

    Add Part ▸ search TP4054 ▸ take the top result ▸ tap the board to place it. It lands as U1 with 5 pads.

    The five pads: power in (VCC), cell out (BAT), ground, a charge-status pin, and PROG, which sets the charge current. Everything else on this board serves those five pads.
  3. Take the support offer

    Tap Place All. Three parts arrive. Here is the list it shows, and what each row actually is:

    The required list: Io Cap pins VCC placed, Io Cap pins BAT placed, Current Set pins PROG placed
    Each REQUIRED row names the pins it serves and reads Placed. “Io Cap · pins VCC” is C1, “Io Cap · pins BAT” is C2, “Current Set · pins PROG” is R1.
    What those parts do. C1 (input cap): wires and batteries have some inductance, so when the charger suddenly draws current the input voltage dips. A capacitor at VCC rides out the dips. C2 (battery cap): the chip’s control loop needs a capacitor on BAT to stay stable. The datasheet requires it, so the app places it. R1 (2 kΩ on PROG): the chip holds about 1 V across this resistor and mirrors that current times 1000 into the cell, so 2 kΩ gives roughly 500 mA of charge current. For a small cell, use a larger resistor: 5 kΩ gives about 200 mA. Choosing that one value is the main design decision on this board.
    And the suggestion underneath: the offer also proposes a USB-to-UART bridge, “on 9 of 18 projects using TP4054.” That number is mined from real open-hardware boards. Suggestions carry their evidence and are never ticked for you.
  4. Read Problems

    Open the right panel ▸ Problems. Four rows:

    Must fix 4: unfinished connection rows for VCC, GND and two automatic nets, each with a locate button
    “VCC has 1 unfinished connection” means C1 isn’t joined to the chip’s VCC pad yet. “GND has 3” means three parts still need a path to ground. The two __PCB_CANVAS_ANON__ rows are connections nobody named: C2 to BAT and R1 to PROG exist electrically, so the app names them automatically.
    After tapping a problem row: the canvas zoomed to the capacitors, a green ring around the located pad, C2 Pad 2 selected with its function and net shown, and pad edit verbs in the left band
    After tapping a problem row: the canvas zooms to the part, rings the pad, and the selection card confirms what is selected. Here that’s C2, pad 2, function GND. At this zoom the capacitors show their 10 µF markings.
    How to use this list: everything on the board is either connected and legal, or on this list with a reason and a locate button. Check it before and after each stage of work, the same way you’d check a compiler’s error list.
  5. Route what’s left

    Enter Route. Tap a pad, tap its partner, then Connect. Repeat for all six connections, in any order; the header counts down to zero. Part 3 shows how to do these six with the auto-router instead.

  6. Export

    Boards ▸ Export for Manufacturing. If connections are still open, the sheet says so and leaves the decision to you:

    The export warning card: 4 blocking, 4 unrouted nets listed by name, text explaining you can still export, with Review Problems and Export Anyway buttons
    The warning names the affected nets and explains the consequence. Review Problems goes back to the list; Export Anyway proceeds with the board as it stands.
    The Manufacturing Files sheet with Bare PCB and Assembled PCB options and Generate PCB Files
    Bare PCB produces Gerbers (one file per copper, mask and silk layer) plus drill files. Assembled PCB adds the BOM, with LCSC part numbers, and the placement file an assembly machine uses to position parts.
    Files are generated and verified on the iPad: outline closed, drills checked, no paired computer involved. The ZIP can be uploaded to a board house as-is.
Where to go next. Same loop, bigger board: the Heltec LoRa clone is five chips and the full radio wiring. Or bring a board you already have: open your KiCad board.