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i.MX 8M Mini USB_VBUS voltage when powering down

Question asked by adevries on Aug 23, 2019
Latest reply on Aug 25, 2019 by igorpadykov

Hello,

 

Can there be 5V on the 30k USB_VBUS resistor when the 8M Mini is unpowered? See image "5V_when_unpowered" for an illustration. If the answer to this question is yes, feel free to ignore the paragraph below. If the answer is no, please read on.

 

When powering down the i.MX 8M Mini, is it important to remove the USB1_VBUS and USB2_VBUS voltage before VDD_USB_3P3 is powered down? I was looking at the 8M Mini eval board, and I realized that VDD_3V3 goes to both VDD_USB_3P3 and controls the load switch for VDD_5V. VDD_5V is what pulls the USB_VBUS detection line high. This means that when VDD_3V3 is powering down, the voltage on VDD_USB_3P3 will drop down to 1.1V before the threshold voltage on NX3008NBKW,115 is reached, turning off the load switch and disabling VDD_5V. So at a certain point in the power-down sequence, VDD_USB_3P3 will be at 1.1V while the USB1_VBUS net is at 5V. I thought that voltage on input pins shouldn't exceed the voltage of their corresponding power group, but this would seem to violate that rule.

 

Can NXP provide any guidance on how to handle the USB_VBUS pins on the 8M Mini? Can the 30k resistor be connected right to the micro usb jack? Since this is USB OTG, it's possible that 5V will be on the jack before the processor is powered up. See image "USB_OTG_VBUS_to_Conn" for a simplified idea of what I'm talking about.

 

Thanks

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