Unknown nRF52805 INFO.VARIANT And DC/DC Regulator Question

[ntennies]

We have a custom board based on the nRF52805 and we're seeing some odd behaviors in debugging / testing that we're trying to nail down. Two questions:

• The INFO.VARIANT of the nRF52805 on this custom board reads "AAA1" (0x41414131). This is not listed as a valid variant in section 4.4.1.9 of the v1.4 product spec for the nRF52805. What's up with that? Is this a documentation issue, is this not a valid variant of the nRF52805, or are looking at some sort of illegitimate clone? Unfortunately, I don't have access to the MCU on the specific article of board I have and so I can't report the markings on the packaging, but I can get those if that would be helpful.
• We just discovered that we had the DC/DC regulator enabled even though this board lacked the necessary circuitry — DCC_A5 is not connected — which we're assuming might explain some of the weird behavior we've seen. Is it possible that running the MCU in this configuration could cause damage to the MCU or external components?

[Håkon Alseth]

Hi,

 

1. It is a second sourcing ID:

https://docs.nordicsemi.com/bundle/PCN/resource/pcn_136_v1.0.pdf

 

This is not reflected in the product specification, my apologies for this inconvenience.

 

We just discovered that we had the DC/DC regulator enabled even though this board lacked the necessary circuitry — DCC_A5 is not connected — which we're assuming might explain some of the weird behavior we've seen. Is it possible that running the MCU in this configuration could cause damage to the MCU or external components?

Starting the DCDC without components in place will effectively place the device in a power-on-reset loop, because the regulator will be starved. It should not cause any permanent damage.

If you have flashed firmware that enables DCDC on a device without having the components in-place, you can try to recover with a nrfjprog loop script (name it nrfjprog_loop.bat):

:loop
nrfjprog --recover -f nrf52
goto loop

 

Kind regards,

Håkon

 

[ntennies]

Håkon,

Thank you for the quick response. 

FYI, with respect to the DC/DC regulator, you say that enabling on a board without the necessary inductors "will effectively place the device in a power-on-reset loop", but we're definitely _not_ seeing that. The MCU runs firmware without a problem in this configuration on the nRF52805, and although it's been several years, I'm pretty sure we also saw the same on our nRF52840 designs, which initially lacked the DC/DC regulator support.

And thank you for the script!