LPC845 under power during operation

[MrVoxis]

Hello everyone,

As part of a project, I'm using the NXP LPC845 with the deep power down mode powered by a battery.

However, while doing some cycling tests, I encountered a problem.

The battery decreases and after a while the product doesn't work anymore. I decided to change the battery, but the product still didn't work.

Is it possible that if the microcontroller's power supply is too low, the flash will deteriorate, rendering the microcontroller unusable?

Has this ever happened to you?

Thank you in advance for the time you will devote to this topic and to the answers you will provide.

See u ! 

[frank_m]

At some point, you will run into a brown-out, the MCU halts because the supply voltage is too low for proper operation.

> I decided to change the battery, but the product still didn't work.

What is you application doing ?
Perhaps you are trying Flash erase/write operations, which increase the power consumption substantially. If a brown-out happens during such an operation, the Flash content might be corrupted.

I would try to read out the Flash, and compare it with the original firmware you flashed it with.

[MrVoxis]

Actually my application performs operations on the flash at very specific and dedicated addresses.

The thing is that I protected the code in CRP2 so it's impossible to read the flash, I'll do this test with the project without this security and I'll let you know

thank you for your reply

[Miguel04]

Hi @MrVoxis 

Are you using a development board or a custom board?

Is it possible that if the microcontroller's power supply is too low, the flash will deteriorate, rendering the microcontroller unusable?

No, low power supply should not be damaging neither the MCU nor the flash. Can you tell me the connections, the battery's voltaje and the project/example you are running? Does the LPC845 still detected by the PC when connected?

Best Regards, Miguel.

[MrVoxis]

Good morning,

Thanks for reply,

I am using the nxp lpc845 for an embedded project. It is not recognized by the pc but this may be due to the CRP2 protection that I put.

I will do the test by removing this protection.

Otherwise the project is powered with a 3.3V flat battery

[frank_m]

> I am using the nxp lpc845 for an embedded project. It is not recognized by the pc but this may be due to the CRP2 protection that I put.

Not sure if you mean on a PC (via USB), or with the toolchain.
The latter, i.e. LPCXpresso or another dev tool, would be my approach to read out the Flash.

Perhaps you can add some instrumentation code for testing, to see where the code fails during startup.

> Otherwise the project is powered with a 3.3V flat battery.

Since CRP is usually a hallmark of a commercial project, you supposedly have the tools to simulate the problem in a lab - i.e. slowly decreasing voltage and increasing internal resistance of the supply.
I think you could speed up the supply drop by orders of magnitude (seconds/minutes instead of weeks/months), and still observe the problem.

[MrVoxis]

First of all, thank you for your answer.

I've already implemented all these things but I'm using the "deep power down" mode and I've lost the debug and other things.

I note that we can use tools to simulate decreasing voltage or increasing internal resistance of the power supply. My colleagues are currently looking for these tools but can't find a "good" solution. Do you have a specific tool to suggest?

Have a nice day.
Bastien

[frank_m · Accepted solution]

> I note that we can use tools to simulate decreasing voltage or increasing internal resistance of the power supply. My colleagues are currently looking for these tools but can't find a "good" solution. Do you have a specific tool to suggest?

I think several programmeable power supplies would easily allow for an endeavour.
But being a software guy, I don't have them either.
But I think a good lab power supply can do the job, turning the voltage and the current limit slowly down manually.

My point is, as the battery voltage decreases, the current capacity decreases simultaneously. The lower the voltage at MCU wake-up, the more drastic the effect on remaining capacity. Environment temperatures have an impact on battery behavior as well.
And Flash erase/write does significantly increase power consumption, making a fail and Flash corruption even more likely.

Though I don't know your application cycles and wake-up events. Perhaps you need to modify it to trigger the issue in a reasonable time in the lab.