FX3 : VBUS/VBATT Power Supplies design

[Anonymous]

Hi everyone,

   

I'm trying to design a board using the FX3 but I got some questions about the VBUS/VBATT supplies. I don't know how I should use it.

   

I want my board to run on batteries so it is not always connected to a computer through the USB3 port (it can be connected if I need to send data to my board over USB or retrieve data over USB). I think I should use VBATT but I'm not so sure.

   

Should I connect VBUS to the USB VBUS line and VBATT to the output of a LDO ? (I'd like to use a LDO to get the 5V voltage).

   

What could the power consumption be if I use almost all the IOs of the FX3 in my design ? How many mA does the LDO need to produce for the VBATT pin in order to make the FX3 working properly ?

   

Thanks for the feedback.

[Anonymous]

Hi,

   

You can connect the USB VBUS from the Computer to the VBUS pin of FX3 and the output of the LDO to the VBATT pin of FX3.

   

Connecting VBUS of Computer to VBUS of FX3 enables VBUS detection in the PC side when FX3 is connected or disconnected. The PC will know whether a USB device is connected or not.

   

If both the VBUS and VBATT are powered, Fx3 by default takes power only from VBUS pin. So, in your case, you need to tell FX3 to draw power from the VBATT pin (LDO) and not from VBUS pin (Computer).

   

So, you need to call CyU3PUsbVBattEnable API in your firmware. You need to call this API before the CyU3PConnectState API.

   

For power consumption estimation, please refer:

   

http://www.cypress.com/knowledge-base-article/ez-usb-fx3-power-consumption-kba85505

   

Regards,

   

-Madhu