Floating VSS on S9S12G48F1

[vadim_unterberg]

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

[lama · Accepted solution]

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

[vadim_unterberg]

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.

[lama]

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

[vadim_unterberg]

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