Building a USB Power Delivery Trigger HAT

Overview

This tutorial shows how to build a compact USB Power Delivery trigger HAT. The board takes power from a USB-C source, negotiates a target voltage, and routes the result to screw-terminal style outputs for downstream electronics.

Why a USB PD trigger board?

USB Power Delivery makes it easy to get a clean regulated rail without a separate DC adapter for every voltage. A trigger board is useful when you want to:

• power a bench project from a USB-C brick
• switch between common rails like 5V, 9V, 12V, 15V, and 20V
• keep the output in a small board that is easy to mount or prototype

The key is to keep the control path simple and the power path short.

Circuit Requirements

For this tutorial, the HAT needs to:

• accept USB-C power input
• negotiate one of several fixed PD voltages
• expose the output on screw terminals
• show an active status LED
• include filtering capacitors near the controller and output rails

Step 1: Place the USB-C input and controller

We start with a Raspberry Pi HAT outline, a USB-C input connector, and a PD controller block.

Step 2: Add the voltage select header

The controller is configured with a small preset header. In a real board, this would be matched to the controller's resistor table or strap options for the target voltage.

Step 3: Add output terminals and status LED

Once the controller negotiates successfully, the selected rail is sent to the output block and the status LED lights up.

Step 4: Add filtering capacitors

Keep the input and output rails calm with one bulk capacitor and one small ceramic capacitor close to the controller.

Step 5: Show the PCB placement

The USB-C connector belongs near the edge. The controller should stay close to the input, while the output terminals sit on the opposite side for shorter power paths.

import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
<RaspberryPiHatBoard name="HAT1">
  <connector
    name="J_USB"
    standard="usb_c"
    pinLabels={{
      pin1: "VCC",
      pin2: "D_NEG",
      pin3: "D_POS",
      pin4: "GND",
    }}
    pcbX={-24}
    pcbY={0}
  />

  <chip
    name="U1"
    footprint="ssop16"
    manufacturerPartNumber="CH224K"
    pcbX={0}
    pcbY={0}
    pinLabels={{
      pin1: "VBUS",
      pin2: "CC1",
      pin3: "CC2",
      pin4: "GND",
      pin5: "EN",
      pin6: "SEL0",
      pin7: "SEL1",
      pin8: "PG",
      pin9: "OUT",
      pin10: "SENSE",
      pin11: "NC1",
      pin12: "NC2",
      pin13: "NC3",
      pin14: "NC4",
      pin15: "NC5",
      pin16: "NC6",
    }}
  />

  <connector
    name="J_VSEL"
    footprint="pinrow5"
    pinLabels={{
      pin1: "5V",
      pin2: "9V",
      pin3: "12V",
      pin4: "15V",
      pin5: "20V",
    }}
    pcbX={10}
    pcbY={10}
  />

  <connector
    name="J_OUT"
    footprint="pinrow2"
    pinLabels={{
      pin1: "VOUT",
      pin2: "GND",
    }}
    pcbX={24}
    pcbY={0}
  />

  <led name="D1" color="green" pcbX={10} pcbY={-10} />
  <resistor name="R1" resistance="1k" footprint="0402" pcbX={6} pcbY={-10} />
  <capacitor name="C1" capacitance="47uF" footprint="1206" pcbX={12} pcbY={8} />
  <capacitor name="C2" capacitance="100nF" footprint="0402" pcbX={12} pcbY={2} />
</RaspberryPiHatBoard>

Bill of Materials

Ref	Part	Notes
U1	USB PD controller	A CH224K / FP28XX / PD2001-style trigger controller
J_USB	USB-C connector	Input power source
J_OUT	Terminal block	Output rail and ground
J_VSEL	Preset header	Voltage selection table
D1	Status LED	Shows negotiated power-good state
R1	LED resistor	Typical 1k current limit
C1	Bulk capacitor	Smooths output transients
C2	Ceramic capacitor	High-frequency decoupling

Testing Procedures

Before you rely on the board, test it in this order:

1. verify the USB-C source is current-limited
2. confirm the selected voltage on the output terminals with a meter
3. check that the status LED turns on only after negotiation
4. try a small load first, then increase current gradually
5. move through the supported voltage presets one at a time

If the output is unstable, reduce load current and inspect the wiring around the controller and the output connector.

Example Code

If you wire the controller's enable or status signal to a Raspberry Pi GPIO, you can monitor the board from Python:

import time
import RPi.GPIO as GPIO

ENABLE_PIN = 18
STATUS_PIN = 23

GPIO.setmode(GPIO.BCM)
GPIO.setup(ENABLE_PIN, GPIO.OUT, initial=GPIO.LOW)
GPIO.setup(STATUS_PIN, GPIO.IN)

GPIO.output(ENABLE_PIN, GPIO.HIGH)
time.sleep(1)

print("power good:", bool(GPIO.input(STATUS_PIN)))

GPIO.cleanup()

Ordering the PCB

Once the schematic and placement look right, generate fabrication files and send them to your PCB manufacturer. Keep the high-current routing short and the USB input path clean.

Next Steps

• add a load switch so the output can be enabled from software
• add an inline current monitor
• support a second output rail
• add mounting holes for enclosure integration