QuickStart REV A power questions/concerns (revisited)

Ron Czapala

I just got a couple of QuickStart boards REV A (from Radio Shack clearance).

Since I recalled seeing posts regarding powering QuickStart boards externally (rather than from the USB port), I have been searching the forums and found several relevant discussions. But I still have some questions/concerns:

QuickStart Rev A

1. Can external power (3.3V) be supplied to pin 38 (VDD) or 4V-9V to pin 40 (VIN) while the board is connected via the USB port without damaging anything?
2. According to the User Guide v1.0, the USB_PWR_EN pin is

   Pulled to USB 5 V supply.Internally driven low after successful USB power negotiation. Can be externally driven low to force the USB power input to drive the QuickStart power supply, such as when powering from a USB charger.

   But this seems to be contradicted by David Carrier in this post where he states REV A

   Does not support USB charging specification, so it can only be powered from a computers USB port, not a USB charger

3. If I wanted to provide power thru the USB port with a power-only cable, I would need to pull the USB_PWR_EN pin 30 low (as in this post), correct?

Forgive me if these questions have been answered before - I just don't want to cause any damage...

David Carrier

Ron,
With either revision of the Propeller QuickStart board, the 3.3-volt supply on pin 38 is directly connected to the output of a linear regulator. If you connect an external 3.3-volt supply to the same pin, it won't damage the regulator or the Propeller QuickStart board, but it you will also need to be sure that you can connect 3.3 VDC to the output of the external supply without damaging it. Rev A boards do not work with USB charges, because they require successful USB power negotiation. Only a USB host can negotiate power and a USB charger does not function as a USB host. You can drive the /USB_PWR_EN pin low to force USB power on.

— David Carrier
Parallax Inc.

Ron Czapala

David Carrier wrote: »

Ron,
With either revision of the Propeller QuickStart board, the 3.3-volt supply on pin 38 is directly connected to the output of a linear regulator. If you connect an external 3.3-volt supply to the same pin, it won't damage the regulator or the Propeller QuickStart board, but it you will also need to be sure that you can connect 3.3 VDC to the output of the external supply without damaging it. Rev A boards do not work with USB charges, because they require successful USB power negotiation. Only a USB host can negotiate power and a USB charger does not function as a USB host. You can drive the /USB_PWR_EN pin low to force USB power on.

— David Carrier
Parallax Inc.

David,
Thanks for your prompt reply. Just wanted to be safe rather than sorry!

localroger

I have put over 50 QuickStarts into industrial control applications with daughterboards that permanently ground /USB_PWR_EN so they can be powered from chargers. I have never had a problem with any of them being hooked up to a computer instead of a charger, including several test articles which have been hooked up to hardly any power but actual computers for program testing for months.