nRF5340 VDD input result in VDDH output DC voltage.

[YF Tsai]

Hi, we use the Fanstel BT40 design a RS232 & USB carrier board, when we use battery 3.3V to VDD, there is a DC2.8V output from VDDH. VDDH should be power input, why there is DC output?

[Martin Sivertsen]

Hello,

In Normal voltage mode VDDH shall be shorted to VDD so you shouldn't have different voltage on VDD and VDDH.

Are VDD and VDDH connected in some way?

Do you have schematics for the board you have made?

Best regards,

Martin S.

[YF Tsai]

Dear Martin

Thank you for the response.
See below for the prats of the schematic include VDDH and VDD. Due to there is another application of VDD, we didn't use the VDD out from BT40.

[Martin Sivertsen]

Hello,

I see that you are not following our reference design guidelines by using VDD as an input when VDD and VDDH are not connected together.
When using VDD as an input (normal mode), VDD and VDDH should be connected together

It looks like you are using VDDH as an input, i.e. in high voltage mode is that correct? In that case VDD would become an output.

Trying to use it outside of spec will yield undefined behavior like you have experienced.

Best regards,

Martin S.