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

[zigenz]

Thinking further, we can use a simple FET-based level converter in the latter case (sourcing from DEC4), ameliorating the requirement for fixing the GPIO voltage.  This will approximately double the current drawn from the DEC4 pin (i.e. require approximately 400 uA).

Note that this requirement is related to a sampling event which occurs for approximately 10 seconds every 15 minutes.