RP2040 Brown-out detection - write to external EEPROM

[dj1zulu]

I have an RP2040 that is powered using a buck converter with a large capacitor. This allows for a delay after a power failure before the voltage drops below the RP2040 minimum.

I am using all the Pins besides GP12.

I have read about some internal Brown-out features in the RP2040, "vreg_and_chip_reset".

Is there a way to identify a power outage ("Brown-out") in the RP2040 without using external pins?

[spaceacejammer]

@dj1zulu

RP2040

Hi dj

I'm not sure what you are trying to achieve but this might be of use:

Arduino Nano RP2040 Connect - determine reason for reset / read rp2040 chip_reset register - SOLVED

Hi, i have a nano connect with some auxiliary circuitry that gets powered from the 3.3v out. This circuitry needs initialization when powered on. On reset the 3.3v will stay active so no need for initialization. This is why i need to determine the reason the nano boots. If from brown out/power loss or due to reset keeping power alive. According to rp2040 documentation page 187 there is a cpu register for that purpose. My question is how do i read from this register? thanks klink

Cheers

[dj1zulu]

I am looking to detect a brownout and take action before the unit shuts down. There are some good methods out there that monitor the voltage and charge (90%) a cap on one of the ADC pins. If a power failure occurs the VSS drops and the voltage on the cap is measured as >90%, in this case, action is taken.

I was hoping to find an elegant way to implement brown-out power failure action as I don't have any pins left.

The reason for this is simple, we have a counter that counts from 0 to 10x10^6, we have an EEPROM for storing the count. we need to avoid excessive writing as the write/clear limit is 100K. we are able to break the count value into parts and span multiple addresses to overcome the write/clear limitation. I don't know how to do this, hence the brownout question.

[Grumpy_Mike]

@dj1zulu

using a buck converter with a large capacitor. This allows for a delay after a power failure before the voltage drops below the RP2040 minimum.

The problem here is that the effect of a big capacitor is wasted because you only get to know about the power failure once the voltage droops to the bring of failure, which is all the brownout will detect. It is much better to use that extra pin to detect that the converter has stopped switching, or its input voltage has gone, that gives you lots of extra time to dump out your data.

[dj1zulu]

Thanks, Mike, the saga gets worse because my buck converter powers the 5V bus on the board which in turn regulates it down to 3.3V.

I plan to put a pnp transistor with some voltage dividers onto the 24V supply and monitor the voltage supply voltage, this way I should have enough time to dump the data .

[Grumpy_Mike]

@dj1zulu

my buck converter powers the 5V bus on the board which in turn regulates it down to 3.3V.

So you just target the prime voltage source for monitoring, or an I missing something?
Sorry but that circuit is just too low a resoloution to actually read anything.

[hzrnbgy]

If it's not too late to change hardware, how about an SRAM/EEPROM combo chip? All you need is an extra capacitor. Unlimited write when powered ON. Only writes to EEPROM during shutdown...

https://www.mouser.com/datasheet/2/268/47L64_Data_Sheet_DS20006168B-1901722.pdf

[dj1zulu]

I have an EEPROM on the board for saving and config and counts,

1809200029_onsemi-CAT24C512WI-GT3_C79986.pdf

My problem is to avoid excessive writing, I am ok to spread the count across many addresses to reduce the write count.

[dj1zulu]

Thanks @Grumpy_Mike targeting the voltage source is a solution