USB-PD vs Traditional USB: Why Power Hubs Don't Exist

This page explains the fundamental differences between traditional USB power distribution and USB Power Delivery (USB-PD), and why you can't simply use a "USB-C hub" to split USB-PD power.

Traditional USB (2.0/3.0) - Simple Power Distribution

Traditional USB hubs were simple because of the fixed voltage system.

AC Adapter (5V)
      │
      ▼
┌─────────────┐
│   USB Hub   │  ← Just splits 5V to all ports
└─┬───┬───┬───┘
  │   │   │
  5V  5V  5V     ← Same voltage everywhere, no negotiation

Key characteristics:

• Fixed 5V - no voltage negotiation needed

• Simple current limits - 500mA (USB 2.0) or 900mA (USB 3.0) per port

• Passive distribution - hub just connects 5V rail to all ports

• Devices draw what they need (up to the limit)

The hub is essentially just a power splitter with some current limiting. Very simple, very cheap.

USB-PD - Complex Negotiation Required

USB Power Delivery is fundamentally different. Each device negotiates its own voltage and current requirements.

Charger (supports 5V/9V/15V/20V)
      │
      ▼
┌─────────────┐
│   USB Hub   │  ← Must negotiate with EACH device separately
└─┬───┬───┬───┘
  │   │   │
  ?V  ?V  ?V     ← Each device wants different voltage!

Device A wants 20V/3A (laptop)
Device B wants 9V/2A (tablet)
Device C wants 15V/3A (zudo-PD)

Why it's complicated:

1. Voltage negotiation per port - Each device negotiates via CC pins

2. Dynamic power budget - Hub must track total power and reallocate

3. Voltage conversion - If charger provides 20V but device wants 9V, hub needs DC-DC converter

4. Each port needs PD controller IC - Adds cost and complexity

5. Re-negotiation - When devices plug/unplug, everything must re-negotiate

Comparison Table

How Multi-Port USB-PD Chargers Actually Work

Multi-port USB-PD chargers are not simple hubs. They have sophisticated internal architecture:

┌─────────────────────────────────────────────────────────────┐
│                    Multi-Port GaN Charger                   │
│                                                             │
│  ┌─────────────┐                                            │
│  │   AC → DC   │  Single main power stage                   │
│  │   (GaN)     │  Converts AC to internal DC bus            │
│  └──────┬──────┘  (e.g., 24V or 48V internal)               │
│         │                                                   │
│         ▼                                                   │
│  ┌─────────────┐                                            │
│  │   Central   │  "Brain" - manages total power budget      │
│  │     MCU     │  Decides how much each port can have       │
│  └──────┬──────┘                                            │
│         │                                                   │
│    ┌────┴────┬────────┬────────┐                            │
│    ▼         ▼        ▼        ▼                            │
│ ┌──────┐ ┌──────┐ ┌──────┐ ┌──────┐                         │
│ │DC-DC │ │DC-DC │ │DC-DC │ │DC-DC │  Per-port converters    │
│ │ + PD │ │ + PD │ │ + PD │ │ + PD │  (voltage conversion    │
│ │ IC   │ │ IC   │ │ IC   │ │ IC   │   + PD negotiation)     │
│ └──┬───┘ └──┬───┘ └──┬───┘ └──┬───┘                         │
│    │        │        │        │                             │
└────┼────────┼────────┼────────┼─────────────────────────────┘
     ▼        ▼        ▼        ▼
   USB-C    USB-C    USB-C    USB-C
   Port1    Port2    Port3    Port4

Key Components

Dynamic Power Allocation Example

Example: 200W charger, 4 ports

Device plugs into Port 1, requests 100W
  → MCU: "OK, 100W available for Port 1"

Device plugs into Port 2, requests 65W
  → MCU: "OK, 65W for Port 2, total 165W used"

Device plugs into Port 3, requests 100W
  → MCU: "Only 35W left! Re-negotiate..."
  → Tells Port 1 & 2: "reduce power"
  → Redistributes: 65W + 65W + 65W = 195W

This is why good chargers (Anker, UGREEN, etc.) publish power distribution tables - the central MCU follows specific rules for allocation.

Key Terms

GaN (Gallium Nitride)

A semiconductor material - alternative to traditional silicon.

Result: GaN chargers are smaller, cooler, and more efficient.

Same 65W output:

┌─────────────┐      ┌───────┐
│   Silicon   │  vs  │  GaN  │
│   Charger   │      │       │
│             │      └───────┘
└─────────────┘
     Large            Compact

MCU (Micro Controller Unit)

A tiny computer chip - the "brain" inside devices.

┌─────────────────────────┐
│          MCU            │
│  ┌─────┐ ┌─────┐ ┌───┐  │
│  │ CPU │ │ RAM │ │I/O│  │  All in one tiny chip
│  └─────┘ └─────┘ └───┘  │
└─────────────────────────┘

• Runs simple programs

• Reads sensors, controls outputs

• Very low power, very cheap

• Found in almost everything: chargers, appliances, toys, cars...

In USB-PD charger: MCU monitors all ports, calculates power budget, tells each port how much power it can provide.

Why You Can't Use a Regular USB-C Hub for Power

A regular USB-C hub (for data) cannot distribute USB-PD power because:

1. No PD controllers - Data hubs don't have PD negotiation ICs

2. No DC-DC converters - Can't provide different voltages per port

3. No power management - No MCU to manage power budget

4. Fixed 5V only - Most hubs only pass through 5V for charging

Bottom line: Multi-port USB-PD chargers exist (each port has its own PD controller and DC-DC converter), but USB-PD hubs that split power from a single upstream source are rare, expensive, and complex.

Implications for Modular Synth Power

For powering multiple zudo-PD units, use a multi-port USB-PD charger (not a hub):

• Each port independently negotiates 15V

• Shared ground eliminates ground loops between cases

• Central MCU manages power allocation

See USB-PD AC Adapter for recommended multi-port chargers.