nRF52840 Q1AAC0 power hardware issue?

[MatthijsvdV]

Hi,

We just received prototypes of a new board with the nRF52840 and now we have a reset problem.

When the board is reconnected after a long time (no voltage remains on the caps) the board works fine, but when the board is disconnected and reconnected after a minute or so, the board does not work. The problem is the DCDC converter on the chip, when it works there is 1.8V on the VDD pins (disconnected from VDDH) but it looks like the DCDC converter is not starting when there is still a low voltage on these pins. Only when it is below 0.1V the board will start again, and that can take some time.

The previous proto boards did not have this problem and we now see that these old boards have chip revision Q1AAD0 (works ok) and now the new boards have Q1AAC0 (does not work ok).

In your errata docs there are [197] and {202} POWER errata for the Q1AAC0. Can this be our problem? If so, how can we fix this for these proto's? Or do we have to resolver new chips with a later revision on the board?

Thanks in advance,

Matthijs

Theftex NL

[Andreas]

Hi Matthijs,

 

Based on just this information, it could very well sound like errata 197 is kicking in here. Unfortunately rev C/1 and D/2 are physically different devices, there are some workarounds that you can try out either for verifying the hypothesis or at least to be able to use your prototypes, but unfortunately to get properly low current consumption you will have to mount revision D devices.

I also noticed that in your design you have 100nF on VDD at pin B1. We have seen in a few cases that not having a larger capacitance close here (1µF in our ref. design) can trigger weird effects, so you could try that also and see if it solves the problem.

 

Best regards,

Andreas

[MatthijsvdV]

Hi, thanks for your reply. You are talking about rev D but we would like to know which version chip we should use for the prototypes and production. On the site we can see there is a version 2-1.3 . Is this the latest version we get, when we order 20.000 pcs? We have to be sure we will not get the wrong chip and we do need to get the same chip in the coming year when we start making 20.000 pcs/month.

On DigiKey etc. we cannot know which revision we will get. How do we make sure we get the correct chip for our prototypes boards?

Thanks,

Matthijs

[Andreas]

Hi Matthijs,

 

Rev 2 (the MP version of engineerin revision D) is the latest and should be used and I was expecting that you should get this now. I would check with the distributor, and see if you need to specify in the order code or something.

I definitely agree that you should get the right revision for any build really, MP or prototype.

 

Best regards,
Andreas