USB to Serial Adapter Question

Can someone tell me what the max current the Vbus (+5v) line can handle on the USB to serial converter?
Thanks in advance.


The serial adapter is set to request 100 mA, which all ports should be able to deliver. The adapter itself draws about 25 mA, so that leaves you with about 75 mA. You can use the Silicon Labs CP2102 tools to change the setting to allow for up to 500 mA, which is the USB limit. Not all ports (e.g. on laptops or on unpowered hubs) will deliver that. The Vbus line is just straight from the USB port, and there is nothing in the hardware of the USB adapter to limit the current (other than the PCB trace width, which can handle over 500 mA).

- Jan

Do you have any more details on how to increase the power requested by adapter? I’ve got a little test project brewing and I need to get a little more juice out of the USB to Serial adapter, but I’m not finding these CP2102 tools you mention.



I haven’t used recent versions of SiLabs tools, but I think this should let you change the power settings:

- Jan

That’s not quite it, but I finally found it on the SiLabs knowledge base. The power requested by the device is set by a single EEPROM byte, which you can change over USB with an application from SiLabs. What you need is:

This Guide
This Program

It includes some DLLs and other developer tools, but basically you run CP210xSetIDs.exe, select your (already plugged in) adapter by it’s serial number from the device list, check the check box next to Max Power, change the hex value, and click “Program Device.” The hex value is in twos of milliamps, so it comes set to 32 (100ma), and you can set it up to FA (500ma).

There was a note in the knowledge base that old versions of the software let you set the byte all the way up to FF, or 510 milliamps, but that “if this occurs, there is no way to recover the CP210x device, as it will never enumerate on the USB bus.” Yikes! They claim the current version keeps you from doing this, but it didn’t complain when I entered FF into the box, and I didn’t hit program to find out!


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