Building a USB Power Delivery Trigger HAT Tutorial

Overview

This tutorial covers designing a USB Power Delivery trigger module that negotiates power from USB-C sources and provides regulated voltage to Raspberry Pi projects. You'll learn about USB PD protocols, sink negotiation, power path design, and current monitoring.

Project Specifications

Parameter	Value
Board Size	25mm × 25mm
Input	USB-C PD (5V/9V/12V/15V/20V)
Output	5V @ 3A or negotiated voltage
PD Controller	FUSB302BMPX
Protocol	USB Power Delivery 3.0

USB Power Delivery Basics

USB PD allows devices to negotiate power delivery beyond the standard 5V:

Voltage Profiles

Profile	Voltage	Max Current	Typical Use
0	5V	3A	Standard USB
1	9V	3A	Tablets, quick charge
2	12V	3A	Laptops, monitors
3	15V	3A	Larger laptops
4	20V	5A	Docking stations

Sink Request Example

// Request 20V @ 3A from PD source
PDO_t request[] = {
    { .fixed: { .voltage = 5000, .max_current = 3000 } },  // 5V @ 3A fallback
    { .fixed: { .voltage = 20000, .max_current = 3000 } }, // 20V @ 3A preferred
};

Components

Ref	Part	Description	Footprint
U1	FUSB302BMPX	USB PD sink controller	`qfn-24`
U2	MP2491C	3.3V/5V buck converter	`qfn-16`
J1	USB-C Receptacle	USB-C connector	`usb-c-16pin`
J2	40-pin Header	Raspberry Pi HAT compatible	`raspberry-pi-hat-40pin`
L1	Power inductor	10µH 4A	`srn6045`
C1	Input capacitor	10µF	`0805`
C2	Output capacitor	22µF	`0805`
C3	Bypass cap	100nF	`0805`
R1	Current sense	10mΩ	`1206`
R2-R3	Voltage divider	100k/100k	`0805`
LED1	PD active	Yellow	`0805`
LED2	Power good	Green	`0805`

Step 1: FUSB302B PD Controller

The FUSB302B handles all USB PD protocol communication:

<chip
  name="U1"
  footprint="qfn-24"
  pcbX={10}
  pcbY={0}
/>

/* USB-C CC pins for PD negotiation */
<trace from=".U1 .CC1" to="net.CC1" />
<trace from=".U1 .CC2" to="net.CC2" />

/* I2C interface to host MCU */
<trace from=".U1 .SDA" to="net.SDA" />
<trace from=".U1 .SCL" to="net.SCL" />

/* Power supply */
<trace from=".U1 .VBus" to="net.VBUS" />
<trace from=".U1 .VConn" to="net.VBUS" />
<trace from=".U1 .GND" to="net.GND" />

/* Interrupt output */
<trace from=".U1 .INT" to="net.PD_INT" />

CC Pin Configuration

USB-C uses CC pins for:

Cable orientation detection: Determines plug orientation
PD negotiation: Communicates power capabilities
VConn: Powers cable electronics (not used in sink)

/* CC1 and CC2 connect to USB-C receptacle CC pins */
/* Rp (source terminator) is inside the USB-C connector */

Step 2: Buck Converter for 5V Regulation

The MP2491C provides efficient 5V from higher PD voltages:

<chip
  name="U2"
  footprint="qfn-16"
  pcbX={-10}
  pcbY={0}
/>

<inductor name="L1" footprint="srn6045" inductance="10µH" pcbX={-5} pcbY={0} />

/* Input capacitor */
<capacitor name="C1" footprint="0805" capacitance="10µF" pcbX={-15} pcbY={3} />

/* Output capacitor */
<capacitor name="C2" footprint="0805" capacitance="22µF" pcbX={-15} pcbY={-3} />

<trace from=".U2 .VIN" to="net.VBUS" />
<trace from=".U2 .SW" to=".L1 .pos" />
<trace from=".U2 .GND" to="net.GND" />
<trace from=".U2 .FB" to=".L1 .neg" />
<trace from=".U2 .EN" to="net.5V_EN" />

Step 3: USB-C Receptacle

<chip
  name="J1"
  footprint="usb-c-16pin"
  pcbX={20}
  pcbY={0}
/>

/* Power pins */
<trace from=".J1 .VBUS" to="net.VBUS" />
<trace from=".J1 .GND" to="net.GND" />

/* CC pins for PD */
<trace from=".J1 .CC1" to=".U1 .CC1" />
<trace from=".J1 .CC2" to=".U1 .CC2" />

/* USB 2.0 data (not used for PD only) */
/* D+ and D+ not needed for PD trigger */

Step 4: Voltage and Current Monitoring

Output Voltage Feedback

<resistor name="R2" footprint="0805" resistance="100k" pcbX={-8} pcbY={8} />
<resistor name="R3" footprint="0805" resistance="100k" pcbX={-5} pcbY={8} />

<trace from=".U2 .FB" to=".R2 .pos" />
<trace from=".R2 .neg" to=".R3 .pos" />
<trace from=".R3 .neg" to="net.GND" />

Output Current Sensing

<resistor name="R1" footprint="1206" resistance="0.01" pcbX={-12} pcbY={0} />

<trace from="net.5V" to=".R1 .pos" />
<trace from=".R1 .neg" to="net.5V_SENSE" />

Step 5: Status LEDs

<led name="LED1" color="yellow" footprint="0805" pcbX={-20} pcbY={8} />
<resistor name="R_LED1" footprint="0805" resistance="1k" pcbX={-22} pcbY={8} />

<led name="LED2" color="green" footprint="0805" pcbX={-15} pcbY={8} />
<resistor name="R_LED2" footprint="0805" resistance="1k" pcbX={-17} pcbY={8} />

<trace from="net.VBUS" to=".R_LED1 .pos" />
<trace from=".R_LED1 .neg" to=".LED1 .pos" />
<trace from=".LED1 .neg" to=".U1 .GPIO1" />  /* PD active indicator */

<trace from="net.5V" to=".R_LED2 .pos" />
<trace from=".R_LED2 .neg" to=".LED2 .pos" />
<trace from=".LED2 .neg" to="net.GND" />  /* Power good */

Step 6: Raspberry Pi Header

<chip
  name="J2"
  footprint="raspberry-pi-hat-40pin"
  pcbX={-10}
  pcbY={20}
/>

/* 5V power output */
<trace from=".J2 .2" to="net.5V" />
<trace from=".J2 .4" to="net.5V" />

/* Ground */
<trace from=".J2 .6" to="net.GND" />
<trace from=".J2 .9" to="net.GND" />

/* I2C for PD status */
<trace from=".J2 .3" to="net.SDA" />
<trace from=".J2 .5" to="net.SCL" />

/* GPIO for PD interrupt */
<trace from=".J2 .29" to="net.PD_INT" />

Complete Circuit

export default () => {
  return (
    <board width="25mm" height="25mm">
      {/* FUSB302B PD Controller */}
      <chip name="U1" footprint="qfn-24" pcbX={10} pcbY={0} />
      
      {/* MP2491C Buck Converter */}
      <chip name="U2" footprint="qfn-16" pcbX={-10} pcbY={0} />
      
      {/* USB-C Receptacle */}
      <chip name="J1" footprint="usb-c-16pin" pcbX={20} pcbY={0} />
      
      {/* Power Inductor */}
      <inductor name="L1" footprint="srn6045" inductance="10µH" pcbX={-5} pcbY={0} />
      
      {/* Capacitors */}
      <capacitor name="C1" footprint="0805" capacitance="10µF" pcbX={-15} pcbY={3} />
      <capacitor name="C2" footprint="0805" capacitance="22µF" pcbX={-15} pcbY={-3} />
      
      {/* Status LEDs */}
      <led name="LED1" color="yellow" footprint="0805" pcbX={-20} pcbY={8} />
      <resistor name="R_LED1" footprint="0805" resistance="1k" pcbX={-22} pcbY={8} />
      <led name="LED2" color="green" footprint="0805" pcbX={-15} pcbY={8} />
      <resistor name="R_LED2" footprint="0805" resistance="1k" pcbX={-17} pcbY={8} />
      
      {/* Current Sense */}
      <resistor name="R1" footprint="1206" resistance="0.01" pcbX={-12} pcbY={0} />
    </board>
  )
}

Firmware (Arduino Example)

#include <Wire.h>
#include <FUSB302_pd.h>

FUSB302 pd;
float voltage = 0;
float current = 0;

void setup() {
  Serial.begin(115200);
  Wire.begin();
  
  pd.begin();
  pd.setMessageCallback([](PDMessage msg) {
    if (msg.type == PD_SOURCE_CAPABILITIES) {
      // Received source capabilities
      for (int i = 0; i < msg.num_pdos; i++) {
        PDO_t pdo = msg.pdos[i];
        if (pdo.fixed.voltage == 20000) {  // 20V available
          // Request 20V @ 3A
          pd.requestPower(20000, 3000);
          break;
        }
      }
    }
  });
}

void loop() {
  pd.processMessages();
  
  // Read voltage and current
  voltage = readVoltage();
  current = readCurrent();
  
  Serial.print("Voltage: "); Serial.print(voltage / 1000, 2); Serial.println(" V");
  Serial.print("Current: "); Serial.print(current / 1000, 2); Serial.println(" A");
  
  delay(1000);
}

Python (Raspberry Pi) Example

import smbus2
import time

# FUSB302 I2C address
FUSB302_ADDR = 0x22

def init_pd():
    bus = smbus2.SMBus(1)
    # Initialize FUSB302
    bus.write_byte_data(FUSB302_ADDR, 0x0B, 0x01)  # Control register
    bus.write_byte_data(FUSB302_ADDR, 0x0C, 0x03)  # Power register
    return bus

def request_20v(bus):
    # Send PD sink request for 20V @ 3A
    # This is a simplified example - real implementation
    # requires proper PD protocol handling
    print("Requesting 20V from PD source...")

def read_voltage(bus):
    # Read voltage from ADC or PD controller
    # Return voltage in millivolts
    return 5000

def read_current(bus):
    # Read current from ADC
    # Return current in milliamps
    return 0

bus = init_pd()
request_20v(bus)

while True:
    voltage = read_voltage(bus)
    current = read_current(bus)
    power = (voltage * current) / 1000000
    print(f"V: {voltage/1000:.2f}V | I: {current/1000:.2f}A | P: {power:.2f}W")
    time.sleep(1)

PCB Layout Guidelines

High-Current Paths

VBUS traces: Minimum 1.5mm for 3A current
Ground plane: Solid ground under entire board
Via stitching: Multiple vias for current return

Thermal Management

Buck converter: Large copper area for thermal pad
Inductor: Keep away from temperature-sensitive components
LED placement: Visible indicators away from heat sources

PD Signal Integrity

CC traces: 0.2mm, keep short (< 20mm)
Decoupling: 100nF near FUSB302 VBus pin
Ground reference: Solid ground under PD controller

Cost Estimate

Component	Unit Cost	Qty	Total
FUSB302BMPX	$1.50	1	$1.50
MP2491C	$0.80	1	$0.80
USB-C Receptacle	$0.20	1	$0.20
Power Inductor	$0.30	1	$0.30
Passives (×8)	$0.02	8	$0.16
Capacitors (×3)	$0.05	3	$0.15
Current Sense	$0.10	1	$0.10
LEDs (×2)	$0.02	2	$0.04
PCB (2-layer)	$0.50	1	$0.50
Total			$3.75

Summary

You've designed a complete USB Power Delivery trigger module covering:

USB PD 3.0 protocol and sink negotiation
FUSB302B PD controller integration
MP2491C buck converter for voltage regulation
USB-C receptacle with CC pin management
Current and voltage monitoring
Status LED indicators
Firmware examples for Arduino and Raspberry Pi

This module enables Raspberry Pi projects to draw power from USB-C PD sources, allowing use of modern USB-C chargers and power banks for higher power applications.

Overview​

Project Specifications​

USB Power Delivery Basics​

Voltage Profiles​

Sink Request Example​

Components​

Step 1: FUSB302B PD Controller​

CC Pin Configuration​

Step 2: Buck Converter for 5V Regulation​

Step 3: USB-C Receptacle​

Step 4: Voltage and Current Monitoring​

Output Voltage Feedback​

Output Current Sensing​

Step 5: Status LEDs​

Step 6: Raspberry Pi Header​

Complete Circuit​

Firmware (Arduino Example)​

Python (Raspberry Pi) Example​

PCB Layout Guidelines​

High-Current Paths​

Thermal Management​

PD Signal Integrity​

Cost Estimate​

Summary​