Can we get the VIO to be 1.3 V?

[xxb9075]

Hi Nordic community:

Can we configure nRF52840 to support a 1.3 V VIO?

I see from the datasheet, after the internal regulator, what supplies to the chip is actually 1.3 V. So can we do it this way:

1. Supply 1.3 V to DEC4 directly. 

2. Power at normal mode, Vdd short to Vddh, and supply also the 1.3 V to Vdd.

3. Disable DCDCEN.

By doing the above steps, can we still run the chip and make it 1.3 V VIO? Or is there another way?

Thanks,

Richard

[Priyanka]

HI Richard,

I don't think we recommend to do it this way, but yes, it can be done. Why do you wish to do this and not as the design? Is there something particular that you are trying to achieve?

Best Regards,

Priyanka

[xxb9075]

Hi Priyanka, 

Thanks for the reply. We want to interface nRF52840 with a customized IC chip with a 0V to 1.2 V power rail. We hope to achieve communication between these two chips without a voltage translator.

May I further ask:

1. Is there any technical concerns if we do it this way? For example, would a 1.3 V supply to the Vdd pin (not for powering the chip, just to define VIO = 1.3 V) affect some functionalities of the chip? Like, would the BLE module be affected?

2. With this configuration, what will happen if we supply a 1.8 V logic high signal to one of the digital pins? Would that result in damage?

Thanks,

Richard. 

[Priyanka]

Hi,

I am afraid what you require is not possible. There is no way to turn off the REG1 regulator. If you disable DCDC, it will use LDO instead. The GPIOs on the nRF52 is run from the VDD power domain, not the DEC4 (1.3V, REG1) power domain. And the VDD specifies 1.7V minium. This means the minimum GPIO voltage to interface other chips will also be 1.7V. At lower voltages the chip will be in a reset state, and non functional. 

So I would suggest you to use a level shifter instead.

-Priyanka