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SN74HC164: GND Current Risk

Zhihong Huang
Intellectual 1550 points
Part Number: SN74HC164


Hi team

When the customer tests the maximum current of pin7, GND, it is found that the instantaneous current is 54.5MA, which exceeds the current of 50mA indicated in the specification. The waveform obtained from the test is as follows:

1.Can the current of 54.5mA cause risk to the chip ?

2. Is there a large margin in the design of SN74HC164, which is more than 50mA in the specification?

Best Regards,

Wesley Huang

Email: wesley-huang@ti.com

  • 0
    TI__Genius 16735 points

    Hi,

    Yes this can cause a risk to the chip. I would recommend trying to reduce the amount of current the device is sinking. Placing a small resistor on the output will help in doing this. There is no large margin on the Abs Max conditions. Operating close to the Abs Max on the device may already be causing damage. So it is best to be well under the Abs Max and as close to the Recommended conditions as possible.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    TI__Intellectual 1550 points

    Hi Karen

    Thanks for your answer.

    1. Do you mean that I should connect a resistor as below?

    2. could you please recommend R value to connect?

    Best Regards,

    Wesley Huang

    Email: wesley-huang@ti.com

  • 0 in reply to Zhihong Huang
    Guru 318700 points

    You should never increase the impedance at the power pins (VCC and GND).

    Put current-limiting resistors at the output pin(s) (Qx) responsible for the high current.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1550 points

    Hi Karen, Ladisch,

    Thanks for your replying. I have a question for you :

    1. The current about 54.5mA, just appears about 2ms, could this short peak current still be a risk ?

    2. My customer don't believe that there is no margin on the Abs of the SN74HC164, so I need some detail description to convince him.

    Do you have any document or application note which can explain the Abs of the SN74HC164 about the risk of exceeding the Abs or why there is the risk if exceeding the abs?  

    Best Regards,

    Wesley Huang

    Email: wesley-huang@ti.com

  • 0 in reply to Zhihong Huang
    TI__Guru 62600 points

    Hi Wesley,

    If operating beyond abs max conditions, TI cannot guarantee the reliability and functionality. The device might very well withstand the surge current but the long term functionality cannot be guaranteed.

  • 0 in reply to ShreyasRao
    TI__Intellectual 1550 points

    Hi Shreyas

    Thanks for your answer.

     I think it would be better if we have the document or application note to explain the Abs of SN74HC164 and what damage it would cause if over Abs.

    Do we have this kind of paper or document?

    Best Regards,

    Wesley Huang

    Email: wesley-huang@ti.com

  • 0 in reply to Zhihong Huang
    TI__Genius 16735 points

    Hi Wesley,

    This is one of the footnotes under the Abs Max table:

    Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

    According to this footnote, operating at Abs Max may affect device reliability. Only operating within the recommended operating condition is the device longevity and reliability guaranteed. 

    It is hard to say how the device will fail and make a application note on this. Every customer has a unique use case and so the device may fail in many different ways. A common issue is when sinking too much current into the output can is it damages the ESD diodes or the output FET.

    Thanks!

    -Karan