nRF52833 GPIO voltage levels in Normal Mode

[zigenz]

Hi there,

We are designing a coin cell (3 V nominal) battery powered product; we'd like the ability to run it all the way down to 2.0 V for maximum lifetime.  To get the most out of the battery, the preference is to run in Normal Voltage mode (1.7 V <= VDD <= 3.6 V) instead of High Voltage Mode (2.5 V <= VDD <= 5.5 V) 

Part of the design requires a 1.8 V reference voltage (nothing particularly onerous in terms of accuracy, ripple etc.).  It need only be a couple of hundred microamps, so a setting the GPIO voltage to 1.8 V and flipping a pin high is a fit-for-purpose approach.

Looking at the nRF52833 PS, it states

In Normal Voltage mode, the GPIO high level equals the voltage supplied to the VDD pin. In High Voltage mode, it equals the level specified in register REGOUT0.

Does this mean the REGOUT0 setting is ignored altogether in Normal Voltage mode?  If so, is there any option to obtain a low current 1.8 V reference in another fashion?

The other alternative is to source our ~200 uA from the DEC4 pin @ 1.3 V; we'll have to adjust our analog components to compensate (we will be running the DCDC).  This however requires fixing a GPIO voltage.  Is this a feasible option?  Thanks.

- Z

[Kenneth]

Hello,

I think I understand what you want, but I see no way to get reliably 1.8V without an external LDO regulator, alternatively that you only allow supply voltage down to 2.5V by feeding VDDH and output 1.8V by using the REGOUT0 register as you indicate.

It's not possible to source any current from the internal decoupling capacitors.

Kenneth