Using nrf52805's DEC4 pin as voltage reference

[lynaghk]

Is it acceptable to use the nrf52805's DEC4 pin as 1.3 V reference?
I've connected the pin across a ~11 MOhm divider to to create a 0.12V reference for an op amp.
I figured the current drawn here would be negligible so it'd be okay, but I'm not able to activate the DCDC regulator.
When I write to the `dcdcen` register at startup, the chip resets.

I'm using the inductors specified in the reference design:

10uH +/- 10% 0603 package
15nH +/- 5% 0402 package

Am I doing something unreasonable here?
Or are there other things I need to setup before I can use the DCDC regulator?

[ketiljo]

No, the DEC4 voltage is not recommended to be used as a voltage reference. Not unless you will have a unreliable reference. The voltage on DEC4 will change depending on the current draw of the inter circuitry. There will also be ripple and the voltage may also not be always accessable.

Can you post a schematic please?

[lynaghk]

The reference is used only to limit current through an LED, it's fine if it fluctuates +/- 20% --- mostly we used it because we had an extra op-amp and the reference "for free" already on the board.

Note we are using the Raytac NRF52805 module, which includes the required capacitor. Our board contains only the inductors.

The 10M resistor should limit the current draw to 10nA or so, which I assumed would have negligible effect. I can assemble some additional prototype boards tomorrow, but wanted to check with y'all first that this design is reasonable in the first place before I keep chasing this down. Thanks for your help!

[ketiljo]

I can't see why it won't work. Do you see a difference in the DCDC behavior if you remove R1?

[lynaghk]

I assembled several more boards and the DCDC regulator works fine, so it appears the problem was a defect in the initial test board assembly. Sorry for the noise and thanks for the help!