K20 USB host power circuit configuration

[marlonsmith]

Hi everyone,

I'm using a K20 chip as a USB host, and I'm trying to figure out how I need to provide power to the USB regulator.  Currently I have Vout33 and Vregin floating. The microcontroller is being provided 3.3V from a regulator on the circuit board.

Since my current configuration isn't working, I've been looking through the reference manual.  I'm thinking about changing my circuit to the following:

- Connect pin Vout33 to Vdd (which is connected to my 3.3V power supply)

- Place a capacitor between Vout33 and ground

Can I get away with doing this, or do I need to provide 5V somehow to the USB regulator?  It sounds like the USB regulator might not be happy with anything less than 3.6V...

Thanks!

Marlon

[marlonsmith]

Hi Paul, thanks for your answer.

Regarding point 1: I am already providing power to the MCU. If I connect Vout33 to Vdd, will the provide power to the USB controller?

Point 2: Do I HAVE to use 5V, or can I leave Vregin floating?

Thanks

Marlon

[Paul_Tian · Accepted solution]

Hi, Marlon

1. Yes,you can connect VOUT33 to VDD. It can provide power to USB controller.

2. You can use 5V for Vregin. If you wants to use USB function, you cannot leave Vregin floating.

Hope my reply can help you.

Best Regards

Paul

[davidburton]

This remains a bit unclear to me.  The data sheet (K20P48M50SF0) claims operating range of Vregin is 2.7-5.5V.

Should there be an exception to this stating that USB will not work with Vregin < ~3.6V?  How much less than 5V can I use and still have USB work?

If I provide external 3.3V to the Vout33 pin and that powers the USB, then why do I still need power to Vregin?  In this case can I just also connect external 3.3V to VregIn and have USB still work?

I have 3.3V on board, but my host controller does not want to provide me 5V over the USB cable.

Thanks.

[marlonsmith]

Thanks Paul, that answers my question.

[Paul_Tian]

Hi, Marlon

1.You can use pin VOUT33 output voltage to provide power to MCU. Please do not forget to add capacitor on pin VOUT33.

2.You can use 5V connect to USB regulator input pin Vregin. The range of USB regulator is from  3.6V to 5.5V.

Hope my reply can help you.

Best Regards

Paul