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OPA1678: thermal pad floating

Amber Si
Intellectual 2165 points
Part Number: OPA1678

Tool/software:

Hi team,

My customer use OPA1678 for single-end to differential signal in audio speaker(mic in ) as below, you can see OPA1678 is supplied by + -5V.

Question: my customer connect thermal pad to AGND, not V- as datasheet requirement. Will it affect the normal work of OPA1678? or if it do affect, can I leave thermal pad floating for working normally?

OPA1678.pptx

BR,

Amber

  • 0
    TI__Mastermind 25210 points

    Hi Amber, 

    I will need to consult with the design team to find out if it can be left floating. 

    The thermal pad must be connected to the most negative supply Vs-.  The thermal pad needs to be connected to the most negative supply and not other potential to ensure proper performance.  Almost all modern semiconductor products use p-substrate process to implement the transistor-level circuitry, which require the p-substrate to be biased at the most negative supply voltage used to power the IC. Thus, connecting the thermal pad (located at the back-side of the silicon wafer) to any voltage above (V-) may result in current leakage that increases at the elevated temperature – see image below.

     

    Best Regards, 
    Chris Featherstone

  • 0 in reply to Chris Featherstone
    TI__Intellectual 2165 points

    Hi Chris,

    Thanks, May I get your confirm if I can leave thermal pad pin floating today? Thanks.

    BR

    Amber

  • 0 in reply to Amber Si
    TI__Mastermind 25210 points

    Hi Amber, 

    Yes the pad can be floating. I discussed this with the product definer and he mentioned it can be left floating but the recommendation would be to solder to a pad on the PCB at least for mechanical stability reasons. Also the pad cannot be soldered to ground or any other potential than VEE. Therefore if they wish to leave the pad floating it should be soldered to a floating pad for mechanical stability reasons. There will be a degradation in thermal performance however the device will still function with the pad floating. 

    Best Regards, 

    Chris Featherstone