iMX9331 serial download without CC controller

[VJ2]

Hi,

we made a custom board using iMX9331. We do not need USB C functionality and do not have CC controller in design. We are facing an issue with the serial downloader. USB1 is not detected on the PC, so the serial downloader does not work. We tested three boards, and all show the same behavior.

The PMIC output rails are OK, and reset is being asserted. By switching the boot mode settings, we are able to read the JTAG ID of both cores, which confirms that the boot mode settings are working. We do not have an SD card provision, so we are unable to test that option.

Regarding the USB configuration: the USB1_ID pin is floating, and USB1_VBUS_3V3 is pulled up to 3.3 V through a 1 kΩ resistor. 

Is CC controller mandatory? We are trying to use USB like this case.

i.MX8MM & i.MX8MQ USB2.0 Design Without USB TYPE-C

Could you please suggest what else we should check? Is it possible that the serial bootloader is getting stuck due to another pin configuration? Also, does the serial bootloader work on LPUART1?

Thank you.

With regards,

   Vishal

[VJ2]

Hi,

Thanks for the reply. We discovered an issue. We had used a wrong FET in USB cable detection circuit, and it was holding USB_VBUS_3V3 low. We removed that FET and tied USB_VBUS_3V3 permanently to VDD_3V3. That solved the issue.

I think this confirmed that we don't need CC controller. Our product is self-powered and does not go to sleep mode due to its application and will not use a USB-detect functionality. Do you think we will have any limitation if we tie USB_VBUS_3V3 to 3.3V?

[JorgeCas · Accepted solution]

Hello,

Got it, thank you for the update.

If your design does not use any of these functionalities, the limitation will not affect you, just keep in mind that it won't be able to use low power operations and won't be able to check connection/disconnection USB events.

Best regards.

[VJ2]

Thanks for the reply.

In case we want to keep USB detection functionality, I see that HW checklist calls for 

If the MicroAB or MicroB USB connectors are used, USBx_VBUS must not connect directly to the 5 V VBUS voltage of the connector. Instead, this pin must be isolated using an external 30 kΩ, 1 % resistor.

Can we connect 5V bus from USB host directly through 30kohms or do we need to create a potential divider to bring it to 3.3V level with 30Kohms and 58kohms?

Regards,

 Vishal

[JorgeCas]

Hello,

I would double check the schematic, could you please share it?

What do you mean with: does the serial bootloader work on LPUART1?

Best regards.