TCA6424A: Floating Thermal Pad

John,

It's fine to connect the thermal pad to ground. That's actually what the datasheet is trying to say when it says it can be either floating or a "secondary ground." The pad is not electrically connected to the die. (That said, we wouldn't recommend tying it to any other voltages besides ground since there is the potential for leakage through the die attach material to the die ground.)

Where is the ESD strike applied? If it is directly to one of the I/O ports, then something like a TVS diode may be useful to clamp the voltage low enough to not stress the device pins. If it is applied elsewhere on the board (or to seemingly unrelated circuits), then there could be noise coupling onto the power/ground lines or to the RESET pin. If that were the case, I'd first try adding capacitance from VCCI to ground and from RESET to ground.

Please let us know once you get the additional info on the ESD tests and if problems persist.

Regards,
Max

Hey John,

There shouldn't be any issue with connecting the thermal pad to GND, in most cases this is recommended as the GND plane is usually large and helps dissipate heat. The datasheet mentions either floating or connected to a secondary GND.

"Additionally, the are currently having an issue where the device keeps resetting when ESD strikes are performed on the board."
I don't have much experience on ESD testing however this device has a reset pin, we may want to see what the reset pin is doing on an o-scope during the ESD event (if possible). If you find out any more information, let us know and I can discuss with engineers who have more experience on ESD on our team.

Thanks,
-Bobby

Hi Max and Bobby,

Thanks for the super quick responses, I really appreciate it! You are making me look like a rock star with the customer :) .

In terms of the wording in the datasheet, that definitely wasn't clear when I read it. It says "If used, the exposed center pad must be connected as a secondary ground or left electrically open." It doesn't actually say anywhere that it can be tied to ground, and it actually reads to me like it should not be connected to ground and that is also what the customer thought when reading this statement. But either way I appreciate you clearing that up. I will let the customer know that this should not cause any issues.

I know it is easier said than done, but I think it would be helpful to make this more clear in the datasheet.

Also, I like the suggestion of monitoring the reset pin and possibly adding more capacitance for filtering on this net and/or the VCC net. I will close this thread and open a new one if I cannot figure our the ESD issue.

Thanks again guys,

John