USB Pin Diagram: Complete USB 2.0, USB 3.0, and USB-C Pinout Reference

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A USB pin diagram maps the signal, power, and ground contacts inside USB connectors, from the four-pin USB 2.0 Type-A to the 24-contact reversible USB-C used for data, video, and power delivery.

USB (Universal Serial Bus) connectors have evolved through several generations, each with distinct pinouts. The most important to understand are USB 2.0 (the baseline standard), USB 3.x (SuperSpeed with additional contacts), and USB-C (the current universal connector).

USB 2.0 Type-A and Type-B connectors have 4 pins: - Pin 1: VBUS (+5 V DC power supply, fused at the host, typically up to 500 mA at USB 2.0 standard, or 900 mA at USB 3.0) - Pin 2: D– (Data negative, differential data line) - Pin 3: D+ (Data positive, differential data line) - Pin 4: GND (Ground/return)

USB 2.0 uses a half-duplex differential signalling pair (D+ and D–) running at up to 480 Mbit/s (Hi-Speed USB). VBUS provides 5 V power; data rates are determined by D+ and D– line states during enumeration.

USB 3.x (Type-A SuperSpeed) adds 5 additional pins to the back of the Type-A connector body, for a total of 9: - Pins 1–4 are retained from USB 2.0 for backward compatibility. - Pin 5: StdA_SSRX– (SuperSpeed receive minus) - Pin 6: StdA_SSRX+ (SuperSpeed receive plus) - Pin 7: GND_DRAIN (Drain ground for shielding) - Pin 8: StdA_SSTX– (SuperSpeed transmit minus) - Pin 9: StdA_SSTX+ (SuperSpeed transmit plus)

USB-C (IEC 62680-1-3) features 24 contacts in a small, symmetrical, reversible connector. Key signals include: - VBUS (4 pins): Power supply, 5 V baseline, up to 20 V / 5 A with USB Power Delivery (PD) negotiation — up to 100 W. - GND (4 pins): Ground return. - CC1, CC2: Configuration Channel pins — detect cable orientation, handle USB PD negotiation, and identify cable capabilities. - D+ / D– (2 pairs, one per orientation): USB 2.0 differential data. - TX1+, TX1–, TX2+, TX2– / RX1+, RX1–, RX2+, RX2–: USB 3.2 and DisplayPort/Thunderbolt SuperSpeed differential pairs. - SBU1, SBU2: Sideband use pins — used for audio, DisplayPort AUX channel, and other alternate-mode functions.

The CC pins are the intelligence layer of USB-C. A standard USB-C cable has a 56 kΩ pull-up resistor on CC to VBUS in the host (source) device; the device (sink) side has a pull-down to GND. The resulting voltage on CC tells both sides what power and data capabilities are present.

USB 2.0 cables have 4 wires. USB 3.x cables add the 5 SuperSpeed wires. USB-C cables vary: basic USB-C cables carry only USB 2.0 signals and limited power; full-featured USB-C cables carry USB 3.2 Gen 2 or Thunderbolt signals and up to 240 W power (USB PD 3.1 Extended Power Range).

How to wire usb pin diagram

Identify the USB connector type Determine which USB connector you are working with: Type-A (rectangular host port), Type-B (square device port), Mini-B (5-pin, older devices), Micro-B (5-pin, smartphones and peripherals), Micro-AB (OTG), or USB-C (reversible oval). Each has a different pinout. The USB-IF publishes official specification documents with precise pinout diagrams for all connector types.
Identify pin 1 on the connector On USB Type-A and Type-B connectors, pin 1 (VBUS) is the first pin counted from the left when the connector opening faces you with the widest face on top. On USB-C, pins are numbered on both sides — the connector is symmetric, and the CC pins identify orientation electronically. Use a USB pinout reference diagram for the exact connector variant.
Measure VBUS voltage (Pin 1) Connect a voltmeter between Pin 1 (VBUS) and Pin 4 (GND) of the USB port. With a host port (computer, charger) and no device connected, VBUS should measure +5 V DC ± 0.25 V. A reading below 4.75 V indicates a voltage drop or a weak supply; above 5.25 V indicates a faulty VBUS regulator.
Test data lines (D+ and D–) On a functioning USB 2.0 port, D+ and D– float at approximately 2.5–3.3 V when idle after enumeration. At the host, both D+ and D– are weakly pulled down to ground through 15 kΩ resistors; the device's pull-up on D+ (1.5 kΩ to 3.3 V) indicates Hi-Speed or Full-Speed capability. Use an oscilloscope to observe USB data signals — they are not meaningfully measurable with a DC multimeter during data transfer.
Identify CC pin state (USB-C only) On a USB-C host port, CC1 and CC2 are pulled up to VBUS through 56 kΩ resistors. On a device side, CC pins are pulled down through 5.1 kΩ resistors to GND. Measure voltage on CC1 and CC2 with a multimeter — the values indicate whether PD negotiation has occurred and which orientation the cable is in.
Verify cable continuity To test a USB cable, use a multimeter in continuity mode. Test each pin at one end to the corresponding pin at the other end. VBUS (pin 1) to VBUS, D– to D–, D+ to D+, GND to GND. There should be continuity on each pair and no continuity between different pin numbers. On USB 3.x cables, additionally test each of the SuperSpeed pairs.
Check for correct shielding and grounding USB cable shielding connects to the connector shell (not to Pin 4 GND directly in the cable — the shield is connected to GND at the connector housing). An open shield on a long USB cable will result in data errors at high speed. Verify shield continuity from shell to shell and verify no short circuit between VBUS and GND or between D+ and D–.

Specifications

USB 2.0 Type-A pins	Pin 1: VBUS (+5 V); Pin 2: D–; Pin 3: D+; Pin 4: GND
USB 2.0 maximum host current	500 mA (standard); 900 mA (USB 3.x); 1500 mA (BC 1.2)
USB 2.0 data rate	Low Speed: 1.5 Mbit/s; Full Speed: 12 Mbit/s; Hi-Speed: 480 Mbit/s
USB 3.2 Gen 2 data rate	10 Gbit/s per lane (20 Gbit/s with dual-lane USB-C cable)
USB-C contact count	24 (including VBUS ×4, GND ×4, CC1, CC2, D+×2, D–×2, TX/RX ×8, SBU1, SBU2)
USB PD maximum power (PD 3.0)	100 W (20 V × 5 A)
USB PD maximum power (PD 3.1 EPR)	240 W (48 V × 5 A)
USB-C CC pull-down resistor (device/sink)	5.1 kΩ to GND on each CC pin

Safety warnings

Never apply voltages higher than the USB specification to any USB port pins. USB VBUS is 5 V (baseline) — applying higher voltages directly to VBUS or data pins will damage or destroy the connected equipment and host controller. USB Power Delivery negotiation to higher voltages must occur through the correct PD protocol on CC pins.
Do not short circuit any USB port pins when probing for measurements. The VBUS rail on a USB host port is typically protected by a polyfuse, but a hard short may damage the motherboard's USB controller or power management circuit.
Be cautious when working with USB-C ports carrying USB PD high-voltage profiles (9 V, 15 V, 20 V, or up to 48 V EPR). After PD negotiation, VBUS can be at substantially higher voltage than 5 V. Equipment connected and then disconnected may have capacitors charged to these voltages.
Counterfeit or non-compliant USB-C cables are a documented fire and equipment hazard. Non-compliant cables with incorrect resistor values on CC pins can trick chargers into delivering excessive current, overheating cables and connected equipment. Use cables that are USB-IF certified or from reputable, verifiable sources.
When designing circuits with USB ports, ensure the VBUS rail has over-current protection (polyfuse or current-limiting circuit) rated appropriately for the USB specification version. USB 2.0 standard host ports are limited to 500 mA per port; USB 3.x to 900 mA; USB BC 1.2 to 1500 mA; USB PD is negotiated.

Tools needed

Digital multimeter (DC voltage and continuity)
Oscilloscope (for USB data signal observation and troubleshooting)
USB protocol analyser (for debugging USB enumeration and data transfer issues)
USB cable tester (continuity test of all pins end-to-end)
ESD wrist strap (when working with USB circuitry on PCBs)
Magnification loupe or microscope (for inspecting USB-C connector contacts)
Soldering iron and fine solder (for PCB connector work)

Common mistakes

Reversing D+ and D– in a custom USB cable: the cable physically transfers data but devices may fail to enumerate or perform unreliably, especially at Hi-Speed (480 Mbit/s). Always verify D+ and D– continuity independently.
Omitting CC resistors on USB-C designs: without 5.1 kΩ pull-downs (device) or 56 kΩ pull-ups (host), the USB-C connection cannot complete its handshake and VBUS will not be enabled. This is the most common oversight in USB-C hardware designs.
Using a USB 2.0 cable for USB 3.x connections and expecting SuperSpeed data rates: USB 2.0 cables lack the SuperSpeed differential pairs (Pins 5–9). Data transfer will revert to USB 2.0 speeds.
Connecting VBUS before GND when making USB connections on powered equipment. Always connect GND first to establish a common reference before applying signal or power lines.
Assuming all USB-C cables support video or Thunderbolt output. A passive USB-C cable may carry only USB 2.0 signals. DisplayPort or Thunderbolt Alt Mode requires a cable specifically certified for that function.

Troubleshooting

Device not recognised when plugged in: Cause: Damaged or incorrect USB cable (D+/D– crossed or open); faulty USB host controller; incorrect CC resistors on USB-C port; ESD damage to D+/D– lines Fix: Test with a known-good cable. Measure VBUS at the port — should be 5 V. Measure D+ and D– — with device connected, D+ should show approximately 2.5–3.3 V (Hi-Speed device pull-up). If VBUS is absent, check host port fuse or power switch. If D+ and D– are both at 0 V, check ESD protection components on the data lines.
USB-C charging at 5 V / 0.9 A only, not fast charging: Cause: CC resistors missing or wrong value; USB PD controller not present or not negotiating; cable lacks E-Marker for high-power rates; charger does not support USB PD Fix: Verify 5.1 kΩ pull-downs on CC1 and CC2 at the device port. Check charger supports USB PD. For power above 60 W, verify cable contains a USB PD E-Marker chip (test by checking the cable datasheet or using a USB-C cable tester that reads E-Marker data).
USB device connects but drops out intermittently: Cause: Marginal cable quality (high resistance in data lines); poor connector contact; EMI interference; overloaded VBUS Fix: Replace the cable with a verified high-quality cable. Measure VBUS under load — should stay above 4.75 V. Check host port current budget. Add VBUS bypass capacitor close to the connector (10 µF + 100 nF). Separate USB cable routing from switching power supplies.
USB 3.x device only achieving USB 2.0 speeds: Cause: USB 2.0 cable used instead of USB 3.x cable; USB 3.x port disabled in operating system or BIOS; SuperSpeed pair open-circuit in cable Fix: Replace the cable with a USB 3.x certified cable. Verify the host port physically has USB 3.x contacts (typically blue-coloured port body or SS logo). Check system device manager to confirm USB 3.x host controller is detected and enabled.
USB-C port sparks or generates heat when cable is inserted: Cause: Short circuit in cable; incorrect VBUS voltage (over-voltage from non-compliant charger); mechanical damage to connector contacts Fix: Immediately disconnect the charger. Inspect the USB-C receptacle for bent or damaged contacts and for foreign matter shorting contacts. Test the charger VBUS output with a multimeter — should measure 5 V without PD negotiation. Discard the cable and charger if either shows damage or out-of-spec voltage.

Frequently asked questions

Why does a USB-C cable sometimes charge slowly even though the port is rated for fast charging?

USB Power Delivery negotiation occurs over the CC pins. If the cable does not contain the correct resistor (or active E-Marker chip for cables above 60 W), the charger and device cannot negotiate higher power levels and fall back to 5 V / 0.9 A default. For charging above 60 W, the cable must contain an E-Marker IC identifying its current rating.

What is the maximum power USB-C can deliver?

Under the USB Power Delivery 3.1 Extended Power Range (EPR) specification, USB-C can negotiate up to 48 V / 5 A = 240 W. Standard USB PD 3.0 supports up to 20 V / 5 A = 100 W. Both require a compliant USB-C cable with an E-Marker chip rated for the current. The baseline USB-C voltage without PD negotiation is 5 V.

Why can't a USB-C cable always carry video or Thunderbolt signals?

USB-C supports Alternate Modes (Alt Mode) — the connector's SuperSpeed lanes can be reconfigured to carry DisplayPort, HDMI, Thunderbolt, or other signals. However, both the host and the cable must support the specific Alt Mode. A generic USB-C cable may carry only USB 2.0 signals. An active Thunderbolt 4 cable or a DP Alt Mode cable is required for video output.

What are D+ and D– on a USB cable?

D+ and D– are the USB 2.0 differential data pair. They transmit data using differential signalling — one carries the signal positive, the other carries its inverse. The receiver detects the voltage difference between D+ and D–, which makes the signal robust against common-mode noise from cables and power supplies. USB 2.0 Hi-Speed transfers data at up to 480 Mbit/s on this pair.

What is the purpose of the ID pin on USB Mini and Micro connectors?

The ID pin (pin 4 on USB Micro-A and Mini-A connectors) is part of the USB On-The-Go (OTG) specification. When the ID pin is connected to GND (as in Type-A plugs), the device acts as a USB host. When the ID pin is left unconnected (as in Type-B plugs), the device acts as a peripheral. The ID pin allows mobile devices to switch between host and device roles.

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