1
\$\begingroup\$

A USB host can generate up to 500mA. Would it mean that the host device is never damaged by a short circuit on a USB guest device? When I play with Arduino, I sometimes see that my PC freezes. The reason was always short circuit over the Arduino board. So often I wonder if I need a tool to limit the current output of my P to protect it from being fried.

\$\endgroup\$
0

2 Answers 2

2
\$\begingroup\$

Would it mean that the host device is never damaged by a short circuit on a USB guest device?

No, it means that USB (2) peripherals must be designed to never draw more than 500 mA.

In fact, they must be designed to not draw more than 100 mA until they have "negotiated" for a higher current allocation from the host.

A good host could be designed to not be damaged if the USB power pins are shorted, but you should not count on this behavior.

\$\endgroup\$
1
\$\begingroup\$

There is an amazing slew of misconceptions and display of bad habits in this question.

A USB host can generate up to 500mA.

Wrong. Any externally-powered USB host MUST generate AT LEAST 500 mA, according to USB Specifications, Section 7.2. It is not uncommon to have 2-3 A from a USB port on a desktop PC.

Would it mean that the host device port is never damaged by a short circuit on a USB guest device?

Yes, in general. Over-current protection of USB ports is mandatory per specifications, see Section 7.2.1.2.1, and the limit is set at 5 A. A good manufacturer (who cares for product usability and no-recalls) would put the protection at lower level, mostly in the form of re-settable polyfuses. This protection will prevent a PC from blasting into flames, but still will make a good spike of current, which might produce a glitch on internal voltage rails (primary +5V rail) and cause temporal malfunction. Good over-current protection with high-side solid-state switches costs a bit more and is less common.

When I play with Arduino, I sometimes see that my PC freezes. The reason was always short circuit over the Arduino board.

From good engineering perspective, you should never "play" with a powered circuit; you either make changes to unpowered circuit and then power it up, or make provisions (like a trimpot on long leads) to make circuit changes without "playing" and shorting your circuit.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.