CH224D USB PD Sink Controller

Understanding the CH224D USB Power Delivery sink controller and how it negotiates voltage with PD adapters.

What is CH224D?

CH224D is a USB PD sink controller - a specialized IC that:

• Communicates with USB-C PD (Power Delivery) adapters

• Requests specific voltages (5V, 9V, 12V, 15V, or 20V)

• Negotiates power up to 100W (with E-Mark simulation)

• Handles all PD protocol communication automatically

Key advantage: You don't need a microcontroller - just set a resistor value and the IC does everything!

How USB Power Delivery Works

Traditional USB Power (Without PD)

USB-A Port → Fixed 5V @ 0.5A-3A (max 15W)

Problem: Limited to 5V, insufficient for high-power devices.

USB Power Delivery (With PD)

USB-C PD Adapter ← Negotiation via CC pins → Device (CH224D)
                     "I need 15V @ 3A"
                     "OK, switching to 15V"
VBUS: 5V → 15V (voltage changes on same wire!)

Result: Up to 100W power delivery (20V @ 5A)

Critical Concept: VBUS is Both Input and Output

This is the most important thing to understand:

┌─────────────┐         VBUS          ┌─────────────┐
│   USB-C     │ ────────────────────→ │   CH224D    │
│ PD Adapter  │   5V (initial)        │  (pin 2)    │
│             │                       │             │
│             │ ← CC negotiation →    │             │
│             │                       │             │
│             │   15V (after PD)      │             │
│             │ ────────────────────→ │             │
└─────────────┘         VBUS          └─────────────┘

CH224D does NOT have a separate output pin!

• Pin 2 (VBUS) is the ONLY power pin

• Initially: VBUS = 5V (default USB voltage)

• After negotiation: VBUS = 15V (or requested voltage)

• Your circuit connects directly to VBUS

This is fundamentally different from DC-DC converters which have separate input and output pins!

CH224D Pin Functions

Power Pins

Communication Pins (PD Protocol)

For PD-only applications: Short DP (pin 8) to DM (pin 9) to disable BC1.2 and other USB data protocols.

Configuration Pins

How DRV Pin Works (Voltage Selection Magic!)

DRV (pin 1) is a weak voltage output (~4.7V) used to determine which PD voltage you want.

The clever voltage selection circuit:

DRV (pin 1) ──┬── CFG1 (pin 19)  ← Connect DRV to CFG1
              │
            Rset (e.g., 56kΩ)
              │
             GND

How it determines voltage:

1. DRV outputs ~4.7V (weak current, can't power external circuits)

2. Rset creates voltage divider between DRV and GND

3. Specific voltage appears at CFG1 (depends on Rset value)

4. CH224D's internal ADC reads CFG1 voltage

5. Based on CFG1 voltage → requests specific PD voltage

Example with our 56kΩ resistor:

DRV (4.7V) ─┬─ CFG1
            │
          56kΩ ← Creates specific voltage at CFG1
            │
           GND

CH224D reads CFG1 voltage → "Ah, user wants 15V!" → Requests 15V from PD adapter

Different resistors → Different voltages:

Rset = 6.8kΩ  → CFG1 = X volts → Request 9V
Rset = 24kΩ   → CFG1 = Y volts → Request 12V
Rset = 56kΩ   → CFG1 = Z volts → Request 15V ✅ (our design)
Rset = NC     → CFG1 = ~4.7V   → Request 20V

Why "weak" output?

• Can drive high-impedance loads (kΩ resistors) ✅

• Cannot drive LEDs, motors, or power circuits ❌

• Just for voltage sensing - perfect for this use!

Simple and elegant: No microcontroller needed - just one resistor tells CH224D what voltage you want!

Power Switching Pins (Internal vs External MOSFET)

CH224D has a built-in MOSFET (rated up to 5A) to switch VBUS power on/off.

How It Works:

For ≤5A applications (like ours at 3A):

• Pin 6 (NMOS#) → GND = Use internal MOSFET

• Pin 5 (GATE) → NC (not connected)

• CH224D's internal 5A MOSFET handles the switching

• Simple and works great! ✅

For >5A applications (e.g., 100W chargers):

• Pin 6 (NMOS#) → Configured for external mode

• Pin 5 (GATE) → Connected to external MOSFET gate

• External high-current MOSFET handles the power

• CH224D controls the external MOSFET via GATE pin

Why external MOSFET? When you need more than 5A, you need a more powerful MOSFET that can handle the high current without overheating.

Current Sensing Pins (Optional Feature)

What they do:

• Can monitor current flowing through the power path

• Useful for overcurrent protection or current measurement

• Requires external sense resistor

Why we don't use them:

• CH224D provides built-in overcurrent protection

• Our design doesn't need current monitoring

• Simplifies the circuit

Connection: Short pins 14 and 15 together, then connect to GND.

VDD Pin - Internal Regulator Output

Pin 7 (VDD) is the output of CH224D's internal 4.7V LDO regulator.

Critical requirement: VDD MUST have a 1µF decoupling capacitor to GND!

VDD (pin 7) → C30 (1µF ceramic) → GND

Why C30 is critical:

• ⚡ Regulator stability - LDO requires output cap to remain stable

• 🔇 Noise filtering - Filters high-frequency noise from internal circuits

• ⚡ Transient response - Provides instant current during load changes

• ✨ Clean power - Ensures accurate PD negotiation and voltage selection

Without C30, the CH224D will not work correctly! The internal regulator could oscillate, causing PD negotiation to fail.

Note: VDD powers only the IC's internal circuits (analog/digital logic). Your external circuits connect to VBUS (pin 2), not VDD.

Unused Pins

Voltage Selection Methods

CH224D supports two configuration methods:

Method 1: Resistor Configuration (Used in This Project)

Simple and static - set once with a resistor value.

Circuit:
DRV (pin 1) ──┬── CFG1 (pin 19)
              │
            Rset
              │
             GND

Voltage Selection:
┌──────────┬──────────────────┐
│ Rset     │ Requested Voltage│
├──────────┼──────────────────┤
│ 6.8 kΩ   │ 9V               │
│ 24 kΩ    │ 12V              │
│ 56 kΩ    │ 15V ✅ (This)    │
│ NC       │ 20V              │
└──────────┴──────────────────┘

CFG2 (pin 13) = Open/GND
CFG3 (pin 12) = Open/GND

Advantages:

• ✅ Simple - just one resistor

• ✅ No microcontroller needed

• ✅ Voltage fixed at design time

• ✅ Low cost

Our design uses 56kΩ → 15V

Method 2: Level Configuration

Dynamic - can change voltage with MCU or switches.

Circuit:
CFG1, CFG2, CFG3 connect to MCU GPIO or VDD/GND

Voltage Selection:
┌──────┬──────┬──────┬──────────────────┐
│ CFG1 │ CFG2 │ CFG3 │ Requested Voltage│
├──────┼──────┼──────┼──────────────────┤
│  1   │  -   │  -   │ 5V               │
│  0   │  0   │  0   │ 9V               │
│  0   │  0   │  1   │ 12V              │
│  0   │  1   │  1   │ 15V              │
│  0   │  1   │  0   │ 20V              │
└──────┴──────┴──────┴──────────────────┘

Note: CFG2 and CFG3 have built-in pull-down resistors

Advantages:

• ✅ Dynamic voltage selection

• ✅ Can change voltage during operation

• ✅ Multiple voltage outputs from same board

Disadvantages:

• ❌ Requires MCU or manual switches

• ❌ More complex

• ❌ CFG voltage limits: <5V for CH224D

USB Type-C CC Pin Configuration

The 5.1kΩ Pull-Down Resistors (R12, R13) - CRITICAL!

Without R12 and R13, your circuit will NOT work! These resistors are the "handshake" that starts PD negotiation.

USB-C Connector:
CC1 ───┬──→ CH224D pin 11 (CC1)
       │
    R12: 5.1kΩ (Rd resistor)
       │
      GND

CC2 ───┬──→ CH224D pin 10 (CC2)
       │
    R13: 5.1kΩ (Rd resistor)
       │
      GND

How USB-C Device Detection Works

Step 1: PD Adapter checks CC pins

PD Adapter sends test signals:
CC1 ──→ Measures resistance to GND
CC2 ──→ Measures resistance to GND

Step 2: Resistance determines device type

Measured Resistance = Device Type:
┌──────────┬─────────────────────────┐
│ 5.1kΩ    │ SINK (wants power) ✅   │ ← This is us!
│ 56kΩ     │ Audio accessory         │
│ Open     │ Nothing connected       │
│ Other    │ Power source or cable   │
└──────────┴─────────────────────────┘

Step 3: Cable orientation detection

• USB-C cables can plug in either way (reversible)

• One of CC1 or CC2 will be the "active" pin (lower resistance path)

• Adapter uses the active CC pin for PD communication

• The 5.1kΩ resistor on that pin tells adapter which way cable is oriented

Step 4: Start PD negotiation

• Only if 5.1kΩ detected → Adapter recognizes device as PD sink

• Adapter initiates PD communication via active CC pin

• CH224D requests desired voltage (15V in our case)

• Adapter responds and negotiates power delivery

What Happens WITHOUT R12/R13?

Critical failure scenario:

No 5.1kΩ resistors:
  ↓
PD adapter sees "open circuit" on CC pins
  ↓
Adapter thinks: "Nothing connected" or "Wrong device type"
  ↓
❌ NO PD negotiation happens
  ↓
❌ VBUS stays at 5V (default USB voltage)
  ↓
❌ Your circuit gets 5V instead of 15V
  ↓
❌ DC-DC converters and power supply don't work!

Why Exactly 5.1kΩ?

USB Type-C Specification defines this value:

• Sink devices MUST have Rd = 5.1kΩ (±20%)

• This is a universal standard that all USB-C devices follow

• PD adapters are designed to detect this specific resistance value

• Not arbitrary - it's carefully chosen to distinguish device types

Tolerance:

• ±20% is acceptable (4.08kΩ to 6.12kΩ)

• We use ±1% for reliability (5.05kΩ to 5.15kΩ)

• Part: 0603 5.1kΩ ±1% resistor (JLCPCB C23186)

Component Specifications

Common Mistakes to Avoid

❌ Mistake 1: Forgetting R12/R13 entirely

• Result: No PD negotiation, stuck at 5V

❌ Mistake 2: Using wrong resistance value

• Result: Adapter misidentifies device type, no PD negotiation

❌ Mistake 3: Only installing one resistor (R12 or R13)

• Result: Cable orientation might not be detected correctly

❌ Mistake 4: Connecting resistors to wrong pins

• Result: CC communication fails

✅ Correct: 5.1kΩ ±1% on BOTH CC1 and CC2 to GND

Summary

R12 and R13 (5.1kΩ pull-downs) are the FIRST thing a PD adapter checks!

Without them:

• ❌ No device identification

• ❌ No PD negotiation

• ❌ No 15V output

• ❌ Circuit doesn't work

With them:

• ✅ Adapter recognizes device as PD sink

• ✅ PD negotiation starts

• ✅ 15V power delivery works

• ✅ Happy modular synth! 🎵

6-Pin vs 24-Pin USB-C Connectors

Full 24-Pin Connector

Pins: VCC, GND (4 each), CC1, CC2, DP, DM, TX/RX lanes, SBU, etc.
Use case: Full USB functionality (data + power)
Cost: Higher

6-Pin Power-Only Connector (Our Choice)

Pins: VBUS (2), GND (2), CC1, CC2
Use case: Power delivery only (no data)
Cost: Lower (~$0.036 vs $0.50+)
Part: C456012 (TYPE-C 6P)

Why 6-pin is sufficient for PD:

• ✅ VBUS pins carry negotiated voltage

• ✅ CC pins handle PD communication

• ✅ GND provides reference

• ✅ No data pins needed for power-only applications

What we lose with 6-pin:

• ❌ No USB data transfer (DP/DM)

• ❌ No alternate modes (DisplayPort, etc.)

• ✅ But we only need power, so perfect!

PD-Only Mode (Why Short DP to DM)

When using 6-pin connector with no DP/DM pins:

Datasheet requirement (Section 5.5):

"If there is no need to use A-port protocols (various protocols realized by DP/DM communication), the DP/DM pin on CH224K/CH224D is required to be disconnected from the DP/DM on the Type-C connector, and the DP pin on CH224 is required to be shorted to the DM on CH224."

CH224D:
Pin 8 (DP) ──┬── Short on PCB
Pin 9 (DM) ──┘

Effect: Disables BC1.2 and other USB data protocols
Result: PD-only operation

Why this matters:

• BC1.2 = Battery Charging specification (uses DP/DM)

• We don't need BC1.2 since we have PD

• Shorting DP to DM tells CH224D to ignore data protocols

• Focuses on PD negotiation only

PD Negotiation Sequence

Step-by-step process when you plug in the USB-C cable:

Step 1: Initial Connection (0-100ms)

┌─────────────┐                  ┌─────────────┐
│ USB-C PD    │ ──── VBUS ────→  │   CH224D    │
│ Adapter     │      5V          │   Device    │
└─────────────┘                  └─────────────┘

VBUS = 5V (default USB voltage)

• Adapter provides 5V default voltage

• CH224D powers up (VDD regulator starts)

• No negotiation yet - just basic USB power

Step 2: Orientation Detection (100-200ms)

CC Pins:
CC1 ─── 5.1kΩ ─── GND  }  CH224D detects which CC pin
CC2 ─── 5.1kΩ ─── GND  }  is active (cable orientation)

• USB-C is reversible (can plug in either way)

• Only ONE CC pin is active at a time

• Active CC pin = cable orientation

• 5.1kΩ pull-downs identify device as sink

Step 3: Capability Discovery (200-300ms)

Device:  "What voltages do you support?"
Adapter: "I have: 5V/3A, 9V/3A, 12V/3A, 15V/3A, 20V/2.25A"

• CH224D sends Source Capabilities request via CC

• Adapter responds with available power profiles

• This is PD protocol communication (digital)

Step 4: Voltage Request (300-400ms)

CH224D reads CFG1 resistor:
- Rset = 56kΩ detected
- Requests: 15V @ 3A

Device:  "I want 15V @ 3A (45W)"
Adapter: "Accepted, switching voltage..."

• CH224D determines requested voltage from Rset

• Sends Request message via CC

• Adapter checks if it can provide that power

Step 5: Voltage Transition (400-1000ms)

VBUS voltage transition:
5V → [ramping] → 15V

Adapter gradually increases VBUS voltage

• Critical: VBUS voltage changes on the same pin!

• Voltage ramps up smoothly (not instant)

• Downstream circuits must handle this transition

• Input capacitors smooth the transition

Step 6: Power Ready (>1000ms)

VBUS = 15V stable
PG pin goes LOW (power good indicator)
System can draw up to 45W (15V × 3A)

• Negotiation complete

• LED1 lights up (PG indicator)

• Main power supply can operate

• DC-DC converters receive 15V input

Design Considerations

Input Filtering

VBUS needs filtering capacitors:

VBUS ──┬─── C1 (10µF) ──→ GND    (Bulk filtering)
       │
       └─── C2 (100nF) ─→ GND    (HF decoupling)

Why both capacitors?

• 10µF (bulk): Stores energy during voltage transition (5V→15V)

• 100nF (ceramic): Filters high-frequency noise, placed close to IC

• Together provide stable power during negotiation

VDD Decoupling

Internal 4.7V regulator needs decoupling:

VDD (pin 7) ─── C30 (1µF) ──→ GND

Why needed?

• VDD powers internal circuits

• 1µF cap stabilizes internal regulator

• Prevents oscillation and noise

• Datasheet requires this!

Power Good (PG) Indicator

+5V ──→ R10 (330Ω) ──→ LED1 (Green) ──→ PG (pin 8) ──→ GND
                                        (open-drain)

How it works:

• PG pin is open-drain output

• Normal operation: PG = HIGH (LED off)

• After successful negotiation: PG = LOW (LED on)

• LED lights up when 15V is ready!

Why connect to +5V instead of VBUS?

• VBUS changes from 5V to 15V

• +5V rail is stable (from linear regulator)

• LED brightness stays constant

• No need to worry about voltage changes

PCB Layout Guidelines

Critical traces:

1. VBUS: Wide traces (≥1mm) or copper pour - carries up to 3A

2. CC pins: Keep traces short, symmetric length, away from noisy signals

3. GND: Solid ground plane, thermal pad (pin 0) with multiple vias

4. VDD: 1µF cap placed close to pin 7

Component placement:

• C2 (100nF) very close to VBUS pin

• C30 (1µF) very close to VDD pin

• R12, R13 (5.1kΩ CC pull-downs) close to IC

CH224 Family Comparison

There are three variants in the CH224 family:

CH224D (QFN-20) - Used in This Project

• Package: QFN-20 (3×3mm)

• Features: Full featured, VBUS up to 22V, GATE pin for NMOS

• Configuration: Resistor or level mode

• Best for: Advanced designs, higher power

• Cost: Medium

CH224K (ESSOP-10)

• Package: ESSOP-10 (larger)

• Features: Similar to CH224D, has VBUS detection pin

• Configuration: Resistor or level mode

• Best for: Through-hole friendly designs

• Cost: Medium

CH221K (SOT23-6)

• Package: SOT23-6 (tiny!)

• Features: PD protocol only, simplified

• Configuration: Resistor mode only

• Best for: Space-constrained, cost-sensitive

• Cost: Lowest

Why we chose CH224D:

• ✅ Small SMD package (good for JLCPCB assembly)

• ✅ Full PD features

• ✅ Resistor configuration (simple)

• ✅ Good stock availability (2,291 units)

Common Mistakes to Avoid

❌ Mistake 1: Expecting a separate output pin

WRONG thinking:
VBUS (input) → CH224D → VOUT (output)

CORRECT understanding:
VBUS (5V input, 15V output) - same pin!

❌ Mistake 2: Forgetting CC pull-down resistors

WRONG: CC1, CC2 → CH224D (no pull-downs)
Result: PD negotiation fails!

CORRECT: CC1 → 5.1kΩ → GND, CC2 → 5.1kΩ → GND
Result: Identified as sink, negotiation works!

❌ Mistake 3: Using wrong Rset value

WRONG: Rset = 24kΩ → requests 12V instead of 15V!

CORRECT: Rset = 56kΩ → requests 15V ✅

❌ Mistake 4: Not shorting DP to DM with 6-pin connector

WRONG: DP and DM left floating
Result: IC may behave unpredictably

CORRECT: DP (pin 8) shorted to DM (pin 9)
Result: PD-only mode works correctly

❌ Mistake 5: Forgetting VDD decoupling capacitor

WRONG: VDD pin with no capacitor
Result: Unstable operation, oscillation

CORRECT: VDD → 1µF cap → GND
Result: Stable internal regulator

Why CH224D is Perfect for This Project

Our modular synth power supply needs:

• ✅ 15V from USB-C PD → CH224D negotiates this automatically

• ✅ Simple configuration → Just one 56kΩ resistor

• ✅ No microcontroller → Standalone operation

• ✅ Power-only application → 6-pin connector sufficient

• ✅ Up to 45W (15V × 3A) → Enough for our DC-DC converters

• ✅ JLCPCB compatible → SMD package, good stock

Alternative approaches would be worse:

• ❌ Fixed 12V adapter → Less portable, requires wall outlet

• ❌ USB-C to DC barrel cable → Only 20V max, needs extra converter

• ❌ PD trigger boards → Usually larger, more expensive

• ❌ Microcontroller-based PD → Complex, overkill for fixed voltage

CH224D = Perfect balance of simplicity and functionality!

Related Documentation

• CH224D Component Page - Full specifications and pinout

• J1 USB-C Connector - Connector specifications

• Diagram1: USB-PD Section - Complete circuit

• USB Type-C Pinout - Understanding USB-C pins

• CH224D Datasheet - Official datasheet

References

• CH224D Datasheet - WCH Official

• USB Power Delivery Specification 3.1 - USB-IF

• USB Type-C Specification - USB-IF