Building a USB Power Delivery Trigger HAT

Overview

This tutorial builds a Raspberry Pi HAT that acts as a USB Power Delivery sink. It uses a CH224K-style trigger controller to request a fixed PDO from a USB-C charger, then routes the negotiated 5V, 9V, 12V, 15V, or 20V rail to an output terminal block. The HAT also includes status indication, input and output filtering, and an optional GPIO header for enable and power-good monitoring.

Circuit Requirements

The HAT should provide:

• A USB-C receptacle connected to a PD sink controller
• Fixed-voltage negotiation for 5V, 9V, 12V, 15V, and 20V charger profiles
• A terminal block for the negotiated output voltage and ground
• Input and output capacitors close to the power path
• A power-good LED so the requested voltage can be checked at a glance
• Optional Raspberry Pi GPIO access to enable the trigger and read PGOOD

How the Trigger Works

The CH224K is a small USB Power Delivery sink controller. It connects to the USB-C connector's CC pins, advertises itself as a sink, and asks the charger for one of the fixed Power Data Objects. The selected output voltage appears on the same VBUS rail after the PD negotiation succeeds.

The three configuration pins, represented by CFG1, CFG2, and CFG3, are pulled down by default and brought to a header. You can populate solder bridges, a DIP switch, or jumpers to encode the voltage option used by your controller variant. Always confirm the exact truth table in the controller datasheet before assembling hardware.

Building the Circuit Step by Step

Step 1: Start with the HAT board

import { RaspberryPiHatBoard } from "@tscircuit/common"

export default () => (
  <RaspberryPiHatBoard name="HAT1">
    {/* Components go here */}
  </RaspberryPiHatBoard>
)

Step 2: Add the USB-C input and PD controller

The USB-C connector exposes VBUS, GND, CC1, and CC2. The controller monitors the CC pins and negotiates the requested output voltage.

Step 3: Add the voltage selector

The voltage selector is modeled as a six-pin header. Three pins connect to the controller configuration inputs, while the other side exposes rails that can be used for jumpers or solder bridges.

<chip
  name="JP1"
  footprint="pinrow6"
  manufacturerPartNumber="3-bit voltage select header"
  pinLabels={{
    pin1: ["CFG1"],
    pin2: ["CFG2"],
    pin3: ["CFG3"],
    pin4: ["GND"],
    pin5: ["VDD"],
    pin6: ["VOUT"],
  }}
/>

Step 4: Add filtering and output terminals

The input capacitor stabilizes VBUS near the connector and controller. The output bulk capacitor sits near the terminal block and helps absorb load steps when the downstream device turns on.

<capacitor name="C1" capacitance="10uF" footprint="0805" />
<capacitor name="C2" capacitance="100nF" footprint="0402" />
<capacitor name="C3" capacitance="47uF" footprint="1210" />
<capacitor name="C4" capacitance="100nF" footprint="0402" />
<chip
  name="J2"
  footprint="pinrow2"
  manufacturerPartNumber="2-pin 5.08mm terminal block"
  pinLabels={{ pin1: ["VOUT"], pin2: ["GND"] }}
/>

Step 5: Add status and Raspberry Pi monitoring

PGOOD drives the status LED through R5. The optional J3 header lets the Pi pull EN low or read whether negotiation completed before enabling a load.

<chip
  name="J3"
  footprint="pinrow3"
  manufacturerPartNumber="GPIO status header"
  pinLabels={{ pin1: ["EN"], pin2: ["PGOOD"], pin3: ["GND"] }}
/>
<resistor name="R5" resistance="2.2k" footprint="0402" />
<led name="D1" color="green" footprint="0603" />

Voltage Selection Table

Use the controller datasheet as the source of truth for the final jumper map. This table is a practical layout worksheet for the HAT:

Target output	Typical use	Layout note
5V	Pi accessories, logic boards	Safest first power-up setting
9V	Small motors, routers, LED drivers	Check downstream regulator rating
12V	Fans, relays, light strips	Use wider copper for higher current
15V	Audio boards, lab modules	Confirm capacitors are rated above 15V
20V	USB-C laptop adapters, buck inputs	Use 25V or higher rated capacitors

Bill of Materials

Ref	Part	Notes
J1	USB-C receptacle	Choose a footprint matching your assembly process
U1	CH224K USB-PD sink controller	FP6601Q/FP28xx or PD2001 can be adapted
JP1	3-bit voltage select header	Replace with solder jumpers or a DIP switch if preferred
J2	2-pin terminal block	Rated for the maximum current you expect
J3	3-pin logic header	Optional Pi-side EN, PGOOD, and GND
C1	10uF, 25V or higher	VBUS input bulk capacitor
C2, C4	100nF	Local decoupling capacitors
C3	47uF, 25V or higher	Output bulk capacitor
R1-R3	100k	Default pulldowns for voltage select pins
R4	10k	Enable pullup
R5	2.2k	LED current limiting resistor
D1	Green LED	Power-good indicator

Example Pi Monitor

The PD trigger works without software, but the Pi can monitor PGOOD before it turns on a downstream load.

from gpiozero import DigitalInputDevice, DigitalOutputDevice
from time import sleep

pd_enable = DigitalOutputDevice(23, active_high=True, initial_value=True)
pd_good = DigitalInputDevice(24, pull_up=False)

while not pd_good.value:
    print("Waiting for USB-PD negotiation...")
    sleep(0.1)

print("Requested USB-PD voltage is ready")

Bring-Up and Test Procedure

1. Leave the HAT disconnected from the Raspberry Pi and set the selector to 5V.
2. Connect a current-limited USB-C PD charger and verify that the status LED turns on.
3. Measure J2 with a multimeter and confirm the expected voltage and polarity.
4. Move through the 9V, 12V, 15V, and 20V settings with no load attached.
5. Add a small dummy load, then re-check voltage droop and component temperature.
6. Only connect a Raspberry Pi or downstream device after the selected voltage is known to be safe for that load.

Safety Notes

USB-PD can expose 20V on a connector that physically resembles a 5V USB port. Clearly label the terminal block, use capacitors with enough voltage headroom, and do not connect the negotiated rail directly to the Raspberry Pi 5V header unless the selected profile is 5V and the power path has been reviewed.