Reviewed against USB-IF specificationsUpdated
Compatibility
Does USB 1.0 use the same four-contact Type-A design?
The classic Type-A receptacle carries 5 V bus power on VBUS, one differential data pair on D-/D+, and ground. USB 1.1 refined USB 1.0, while USB 2.0 retained the connector and pin order and added the 480 Mb/s High Speed signaling mode. A USB 2.0 plug can therefore mate with a USB 1.x receptacle, with the link negotiating the fastest mode supported by both ends.
Do not confuse the shell with the protocol
A black, white, or blue insert is only a convention. Contact count, controller capability, and product documentation are stronger evidence.
How much current can it supply?
There is no single current rating for every USB-A receptacle. The USB power policy, port type, cable resistance, host power budget, and the connector manufacturer's contact rating all apply. For a normal enumerating data port, these are the useful reference limits:
| Port / state | Before configuration | After configuration / detection | What it means |
|---|---|---|---|
| USB 1.x / USB 2.0 | 100 mA | 500 mA max | One 100 mA unit load initially; up to five unit loads after the host accepts the request. |
| USB 3.x Standard-A | 150 mA | 900 mA max | Applies to a SuperSpeed-capable standard downstream port, not automatically to a four-contact USB 2.0 port. |
| USB BC 1.2 | Detection required | up to 1.5 A | A charging downstream port or dedicated charging port; this is a separate battery-charging specification. |
500 mA is not available merely because the connector fits. A bus-powered USB 2.0 device should remain within one unit load before configuration and request additional current through its descriptors. Likewise, drawing 1.5 A requires BC 1.2-compatible detection and source behavior. Proprietary charging schemes may differ and are not guaranteed by USB 2.0.
USB 2.0 also imposes a much lower suspend-state budget: a suspended device must average no more than 2.5 mA from VBUS, excluding the permitted short transition interval. Remote-wakeup capability does not remove that limit.
How do USB 1.x, USB 2.0 and USB 3.x Type-A differ?
USB 3.x preserves the original four contacts so older USB 1.x/2.0 plugs still mate and operate. Its additional five contacts carry two SuperSpeed differential pairs and a signal ground. If only the original four contacts are wired, the connector is not a functional SuperSpeed port even if its insert is blue.
Design notes
Receptacle viewing direction
Pin numbering depends on whether the drawing shows the mating face, PCB side, top, or bottom. Confirm the footprint against the connector datasheet before routing a board.
D+ and D- routing
Route the pair together with controlled differential impedance, minimal skew, few discontinuities, and short stubs. Add suitable ESD protection close to the connector.
VBUS is nominally 5 V
Use power switching, current limiting, reverse-current protection, and adequate trace width where the product architecture requires them. Never back-feed a host port unintentionally.
Connector current rating
The USB protocol limit does not override the hardware rating. Check the selected receptacle's per-contact current, temperature rise, contact resistance, and mating-cycle specifications.