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LP2981: Placing a TVS diode between pin 4 (NC) and pin 5 (OUT)

Part Number: LP2981
Other Parts Discussed in Thread: TPS7A24

Hi team,

for certification reasons, customer had to place a TVS diode between pin 4 and 5 of LP2981.
This was necessary for passing EFT test.

Which type of issues can be expected by putting a TVS over pin 4 and 5?

Are there drop-in-replacements which do not have an EFT-sensitive pin?

Thank you for your help!

BR,
Stefan

  • Hi Stefan, 

    The NC pin (Pin 4) of LP2981 must be left floating and if connected through a TVS to Vout, the output voltage could be shifted. 

    For the drop-in alternative, what's the input voltage, output voltage, and Iload? 

    Regards, 
    Jason Song

  • Hi Jason,

    Thank you for this info!
    Can you give an estimation of how much the output voltage can shift?

    It would be great to know

    • how much the output voltage will change due to noise/drift/’wobbling’.
    • how much transient regulation is affected (and if maximum Iload is dropped)
    • if the LDO could get significantly hotter (and go in a fail state)

    Regarding the replacement, here are the requirements:
    Vin is about 5.1-5.5V

    Vout is 3.3V fixed and 5.0V fixed,

    Iload (total) is expected to be between 50-150mA (not sure what the balance is between the 3.3V and 5.0V)

    BR,
    Stefan

  • Hi Stefan, 

    The NC pin is directly connecting to the programming bits that control the accuracy of the LDO. We know that when the NC pin is grounded, the accuracy would change by 0.75%. With a TVS, if the NC pin is also connected to the GND, we would expect a similar 0.75% shift on the output voltage. The other AC performance like transient regulation will not be affected. 

    I will get back to you soon with the potential alternative that does not have a floating pin. 

    Regards, 
    Jason Song

  • You may consider using TPS7A24 as a P2P solution to replace LP2981 and the NC pin in TPS7A24 has no internal connection. 

    ~Jason