nRF52840 REG0 voltage accuracy

[AriS]

I have a couple of questions regarding the nRF52840 internal voltage regulators, specifically REG0. I couldn't find the answers from the datasheet and therefore I hope that the experts at this forum can help me.

We are currently developing a device that is powered from a 3.7V Li-ion battery. The plan is to use REG0 in high-voltage DC/DC mode for generating the 1.8V VDD supply and also to provide power for some external circuits. Now I'm a bit confused, because when I'm reading the electrical specifications it states that "VDD output voltage error (deviation from setting in REGOUT0 on page 46)" is min. -10% and max. +5%. Does this mean that I should use some other setting than the nominal 1.8V as the REGOUT0 register value in order to have some margin on top of the VDD minimum voltage specification (1.7V)? On the other hand the REGOUT0 register has only a few rather coarse options for the voltage setting (the next one is 2.1V), so does this mean that I should use it instead of 1.8V in order to eliminate the risk of having too low supply voltage due to tolerance variations?

Also what confuses me is the similar voltage value (1.8V) for REGOUT0 settings 0 and 7 (default). Does this mean that there is no difference at the output voltage regardless of which one of the settings is used?

[Jared]

Hi,

The minimum voltage is taken in consideration and there shouldn't be a case where you have a significant error on the output voltage from REG0 when it's 1.8 V which would cause the chip to not function properly. In short, this means that you can safely use the 1.8 V output voltage from REG0.

regards

Jared 

[Marien]

Hi I understand that the default 1.8Volt for DCDC0  or Reg0 is working properly for the nRF52840 it's self. In My design case I connect an external small sensor, powered bij VDD-NRF  (this 1.8Volt)  Thsi device requires  minimal 1.7 Volt. Of course I prefer to not lower below 1.75 Volt to be sure and allow some voltage loss.
With the specification -10%  I will not meet this voltage at all.
So what is the minimum tolerance?  

[Jared]

Hi,

The -10% is generally for all outputs for REG0. REG0 at 1.8 however is a bit different. The REG0 at 1.8 is even more precise as the output of REG0 is also VDD. The nRF52 itself requires VDD > 1.7V for it to function properly. You could therefore assume that the REG0 at 1.8 is very precise with very little variation.

regards

Jared  

[Marien]

Hi  Jared,  I Do realy assume this,  but for a design in is only the datasheet reliable. if 1 in 1000 product fail due to a lower VDD we have a problem...  Or we must test all products.
I hope Nordic can write an errata.

[Jared]

Hi,

I agree it could have been documented better. We'll discuss this internally.

best regards.

Jared 

[ble_alex]

I'd just like to see if there is any more information available regarding the REGOUT0 voltage range for the nRF52840.  My application is using the REG0 in LDO mode with 3V output, and I'd like to better understand if the -10% +5% is the most accurate to plan around.  If the range is actually tighter at this voltage, or while using the LDO, or across a specific temperature range, it would be really useful information

[Jared]

1V8 is the only option where the variation is less due to what I mentioned earlier in this discussion. You can safely consider what is specified in the product spec as the most accurate for all other options for the output of REG0