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TPS782: TPS78218DRVT Grounding pin 5

JPAlleyne
Expert 1565 points
Part Number: TPS782

Hi, in error I have only grounded pin 3 and the thermal pad for this part, but failed to ground pin 5. This is causing the regulator to produce 2.2V instead 1.8V. I currently have the VDDIO pin of a DS90UB925 connected to this regulator that can handle 1.8V +/- 5% or 3.3V. IDDIO is 1.6mA (Max). It currently does not use any outputs only its inputs and where V input high is 0.65 * VDDIO. The inputs to the DINX pins of the DS90UB925 are 1.8V. Here are my questions:

1) Given the low load current of 1.6mA (Max) on the regulator, can I expect the regulator to be stable at 2.2V even though pin 3 is not grounded?

2) Should I be worried if I supply 2.2V to the VDDIO pin of the DS90UB925 even though it is outside of the recommended voltage range, but still well below absolute max?

Everything is currently functional, but I am considering if there could be any long term repercussions.

Thank you,

JP

  • +1
    TI__Genius 14245 points

    Hi JP,

    Unfortunately, we cannot recommend that the TPS782 be used without all the GND pins being tied to GND. All testing and verification was done with both pin 3 and in 5 tied to GND. I tried to find some design documentation on why the two grounds exist however this is an older family of devices I wasn't able to find this information.

    As we can see from your use case by leaving pin 5 open there appears to be an offset in the output voltage causing it to be 22% higher than the set point. It could be that only the resistor divider for the output is affected by this, however that seems unlikely and we don’t know what other circuits may be seeing more resistance in their GND path and so cannot recommend using the device outside the datasheet recommendations. 

  • 0 in reply to Kyle Van Renterghem
    Expert 1565 points

    Thank you, I understand.