LPC Link 2 destroys MCU when flashing

[jana_beck]

Hello,
I am having a very strange behavior.
When flashing my custom board, that has a LPC540 on it, the MCU gets destroyed.

1. Setup:
 - The custom board is powered via PoE. That voltage is brought down to 3.3V.  I measured this voltage as well as ripple and it is all good.
- A LPC Link2 is connected via a 10 Pin JTAG header

2. Test:
-2.1: No PoE and setting JP2 (and therefore powering the custom board from the LPC Link2) and flashing the MCU works.

2.2: PoE and not setting JP2. Everything is ok, until I flash the MCU. The board gets destroyed (I cannot talk to the MCU at all anymore and the PoE stops working as well (cycling on and off)
2.3: PoE, setting JP2, but separating the power (3.3V) coming from the LPC Link2 from the power (3.3V) on the custom board. Same behavior as 2.2.

2.3: PoE and setting JP2. Flashing works.


Can anyone tell me why this is happening and also why this is only happening when I try to flash?
When I set JP2, the LPC Link2 is already outputting 3.3V to my custom board, so why is this only happening once I flash?

Any help appreciated!

[frank_m]

With "destroyed", do you mean physically destroyed (casing blown, short circuit, high impedance), or just "no target detected" ?

And with PoE, you mean power-over-ethernet ?

If yes, you might have a problem with your power supply, perhaps a GND potential issue.

[jana_beck]

1. The MCU does not work at all after flashing. Flashing destroys something on the board. After flashing, the 3.3 V power repeatedly turns on and off (which is I assume the PoE switch trying to output power, detects a failure and retries again.

PoE= Power over Ethernet.
I need to double check thee GND potenial issue you are mentioning.

What I still do not understand is, why this is happening only once I flash the MCU.
Also, why is this not happening at all if I keep JP2 connected?

[frank_m]

I would suggest to first check the power consumption.

I had not been working with NXP Cortex M devices for years, so I'm not an expert, to put it that way.

But your board might just be virtually bricked. Either the application is uncooperative (sleep modes often cause problems), or the Flashis corrupted, and the device starts into a ROM system bootloader.

I would try a mass erase, don't know what specific tools NXP offers in this case. But this was the way to go with other Cortex M devices I worked with (ST, Fujitsu/Cypress, Atmel).

[jana_beck]

Ok, I will keep debugging.

My go to at the moment is not to use PoE and flash the MCU at the same time.

Since PoE and the LPC Link2 will not be connected at the same time during manufacturing, I am not that concerned about it anymore.
Still a weird behavior and worth looking into.

Thanks for your suggestions!