USB PC Current Limit


I want to build a USB device that can draw 1A.

Some of the PCs at my office can supply 1A, some only 800mA. The USB 2.0 specification says a device can only draw up to 500mA.

I cannot build a software/hardware infrastructure to check if the device is a PC and, if so, to limit the current to 500mA.

What would happen if I try to draw 1A without checking if the host is capable of supplying this current? Does this risk ruining the host?

Best Answer

USB 2.0 standard which permitted 100/500 mA was eventually extended with Battery Charging Specification which allows the device to draw up to 1.5A after it sees that the other side (the plug pack) is shorting D+ and D-.

Some PCs may be able to source more than 500mA, but it is not safe for them. And some will allow only 100mA prior to enumeration.

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