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Changing the nRF51822's supply voltage at runtime

Eliot Stock

We have an application in which it would be nice to change the supply voltage for our Nordic module (nRF51822 running the Soft Device) depending on which other modules on our board are powered up and in use. This is because the other modules have higher operating voltages and we have UART comms going on with both of them. If the Nordic voltage is too low, we can't reach logic high on the TX and RX lines for these modules. But these modules aren't powered up for much of the time so when they're not, we'd like to conserve power by running the Nordic at the minimum 1.8V.

Supposing our power supply has a GPIO line to it from the Nordic and I can switch from 1.8V to 3.0V by setting that line high. Is there any problem with doing this while the Nordic is running? How will it cope with a sudden leap in supply voltage like that? (There's filtering on the power supply of course, so perhaps not that sudden.)

Also, are all the GPIO lines going to be low by default at the time the Nordic is powered on?

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    Hi Eliot,

    Dropping the voltage from 3.0 -> 1.8V will not be a preferred solution for your issue. This drop in voltage is to be considered as a voltage ripple, which we do not have a hard specification for, but we recommend that the ripple on VDD is within 100 mVpp.

    A more preferred solution is to use a level shifter (discrete via two transistors on RXD/TXD or a IC solution).

    Regarding the GPIO state; when you're powering up, the nRF is in a RESET-state (which is a undefined state), where the GPIOs are undefined. When the chip has successfully powered up, the GPIOs are disconnected (internally) by default (hi Z).

    Cheers, Håkon

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