nRF52840 Output Power

[Kevin01]

A customer implemented a nRF52840 (QIAA package) and says the output power is about 10dB lower than expected.  Having done multiple nRF52 designs with good results, I reviewed their schematic and layout and observed that it generally looks pretty good.  The only obvious concern I found is that they do NOT have the VDDH pin connected.  They are powering VDD with 3.3V and otherwise following the Normal Voltage mode with DC/DC (except that the Supply is only connected to VDD and VDDH is Not Connected).  Could that cause the output power to be out of spec?

I've only reviewed their HW design, but they may also have a SW issue which has not yet been investigated.

[Priyanka]

Hi Kevin,

For Normal voltage operation, the VDDH needs to be connected to the same 3.3V supply as VDD.

Leaving VDDH unconnected or floating while in Normal voltage mode is not a supported configuration.

I would suggest them to try this first, though this issue alone should not actually cause a 10dB reduction in output power.

If even after connecting VDDH and VDD they are facing this issue, then please check the software side, i.e. whether the radio is properly configured for the transmit power.

And they could also check the antenna and the matching network, whether it follows the reference design and also complies with the antenna manufacturer's recommendations (this can be checked from the antenna's datasheet).

-Priyanka