Applying voltage to VBUS before VCC

[Andrew Mowry]

In my design I have a load switch that supplies power to VCC. The result is that voltage is applied to VCC 0.6 mS after 5V is applied to VBUS, because the load switch takes that much time to turn on. Will that be a problem? Thanks!

[Priyanka]

Hi Andrew,

That should be fine. Are you working with a custom hardware based on 52840 SoC or with the 52840DK?

Best Regards,

Priyanka

[Andrew Mowry]

Great, thank you! I am working with a custom board using the ISP1807 module.

[Priyanka]

Ah okay. Supplying the voltage to VBUS before VCC is okay because the VBUS input is used for a regulator, and this regulator is used by the USB peripheral in order to supply voltage to the data lines. This regulator is switched on only after the peripheral is configured. So it's fine.

[Andrew Mowry]

Great, thanks again for your help!

[michaelrommel]

Hello,

I may be reviving an old thread, but that is most closely related to what I was looking for...

I have designed a keyboard around the nRF52840. The VDD is being used, not the VDDH. If the keyboard is attached to USB, VBUS is fed into a battery management IC and charges a LiPo battery, also goes into a LDO and the stabilized 3.3V VDD is fed to the nRF. If the keyboard is not connected to USB, it is powered through the battery management IC -> LDO -> VDD.

My question: In order to shut off the keyboard and prevent draining the battery, I have a switch cutting the power path between the LDO and the VDD net.

Is it OK to have the switch off and still have the device connected to USB, feeding power into the VBUS pin although there is no power going to the VDD pin? I am not concerned about eventual power consumption of the nRF52840 chip itself, only if this a supported or unsupported configuration.

Thanks for any responses and if I shall rather open a new thread with this question.

  Michael.