S12 / MagniV MicrocontrollersのトピックRe: Floating VSS on S9S12G48F1

Floating VSS on S9S12G48F1

vadim_unterberg — Mon, 11 Sep 2023 08:17:33 GMT

Hello dear community,

I have a question, which came up during our failure simulation re-tests with the [S9S12G48F1MLC] microcontroller.

Removing the [Pin 5], which is the VSS (GND) connection of the device, does not cause any failures. The microcontroller sub-circuit continues to work without any issues.

The datasheet however clearly states in chapter [10.2.4], that pin 5 has to be tied to GND.

So what happens, if the connection is removed due to a cold joint for example. There is no mention of that. My guess would be, that the µC finds itself an alternative GND. As far as I know, there are packages where VSS and VSSA are tied together internally, that should not be the case here. SO, either the external VSSA connection, or one of the grounded GPIOs.

- But is that supposed/allowed to happen?
- Does this damage the µC?
- Is there a way to avoid or detect this failure mode?

Any input or confirmation would be highly appreciated.

Bist regards
Vadim

Re: Floating VSS on S9S12G48F1

lama — Mon, 11 Sep 2023 16:30:53 GMT

Hi,

the connection to other VSS_ pins is performed also internally but not via wire but via ESD diode or some structures. The connection is not allowed to accept a load current so external connection to the GND MUST be done. Yes it can damage the MCU because it is a ticking time bomb with a random count down value.
Best regards,

Ladislav

Re: Floating VSS on S9S12G48F1

vadim_unterberg — Fri, 29 Sep 2023 15:11:54 GMT

Hello again,
and thank you very much for the reply. I was kind of expecting something like that.
The question now is, how to best handle this situation? I cannot think of any test or detection method for this particular case.

Any suggestions?

Best regards
Vadim

PS: It is a nice and vivid metaphor you used there, special thanks for that.

Re: Floating VSS on S9S12G48F1

lama — Mon, 02 Oct 2023 08:58:58 GMT

Hi Vadim,

for this case there is no suggestion except for the high quality of the soldering process.

We really do not know about any workaround.

Best regards,

Ladislav

Re: Floating VSS on S9S12G48F1

vadim_unterberg — Wed, 04 Oct 2023 06:11:03 GMT

Hello Again,

that is unfortunate, but I have seen that coming.
I guess the topic is closed then.
Thanks a lot for your input and with best regards,

Vadim