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Original question:

LM25066A: How to decrease the instaneous overshot of input voltage on LM25062/6

LM25066A: cancel TVS on LM25062/66

Richard Yang1
Intellectual 1100 points
Part Number: LM25066A
Other Parts Discussed in Thread: LM25066

Hi Team:

 it is known we will propose customer to use a clamped TVS to suppress the voltage energy when transient or hot wrap activity occurs, However, some Practical running results shows that once the TVS is failed to be short potentially, the end customer's system will shut down by the 12Vin BUS, which is a fatal system problem, end customer can let one rail of the 12V Efuse(LM25062/6) to be open when failure occurs but not affecting the 12Vin BUS's other server boards, so, end customers has great worry on the use of TVS at the front of Efuse (LM25062/6)side.

So, the problem we face is :

 if  TI customers want to discard using TVS at the front end of LM25062/6, do we have other solution to fix the original issue? or if we do not have the good solution and just delete TVS, Can we promise that LM25062/6 is safe during the worse case?

can you help to check if it is possible in the case that customer may switch to other competitors and there is no TVS.

Thanks very much!

 

  • 0
    TI__Guru 57737 points

    Hi Richard,

    I will get back to you tomorrow.

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Richard,

    Any electronic IC will fail if they are subjected to conditions beyond their designed limits/ Absolute maximum ratings. The reason why we recommend to use a TVS in front of Hotswap is to protect the device from Transient over voltages which can be greater than the Absolute maximum ratings.

    Similarly, TVS also fails if it is operated beyond its rated conditions. TVS are the best over voltage protection devices which act almost instantly for over voltages and prtect the down stream circuit. It is difficult to find a replacement for TVS to protect the Hotswap.

    So, the key to protect the Hoswap and TVS here is make sure that you select the right TVS. The below attached document will help you in selecting the right TVS for your application.

    8877.TVS Clamping in Hot-Swap Circuits.pdf

    In case you decide to remove the TVS, you need to be 100% sure that the transient over voltages are within the Absolute Abs Max rating of the device. This not only applies to LM25066/2 but also to all competitors devices. 

  • 0 in reply to Praveen GD
    TI__Intellectual 1100 points

    Hi Praveen:

      the current situation is the end customer do not allow to use TVS, can you help to give your evaluation results on the max value for LM25066/2?

    can do have other solution to protect the chip, but not for the MOS. how about using a resistor or FUSE in series with TVS ?

    Thanks!

     

  • 0 in reply to Richard Yang1
    TI__Guru 57737 points

    Hi Richard,

    The Maximum Absolute Rating of Vin and Sense pins for LM25066 are 24V. So, the controller can withstand voltage transient spikes upto 24 V. The Maximum Absolute Rating of Vin and Sense pins for LM25062 are 20V. So, LM25062 can withstand voltage transient spikes only upto 20 V.

    If the transient over voltage spike is less than Absolute Maximum rating, you can avoid using TVS but you need to thoroughly test your circuit in all conditions to be sure about this.

    Otherwise, as you said you can consider using a Fuse in series with the TVS diode.

  • 0 in reply to Praveen GD
    TI__Intellectual 1100 points

    Praveen:

    can you help to verify the following if no TVS is used?  thanks again!

    *******************************************************

    1. Which Pin will be damaged;

    2. The IC damage happens application conditions;

    3. One 10nF ~100nF will be helpful or not?

  • 0 in reply to Richard Yang1
    TI__Guru 57737 points

    Richard,

    1. If the voltage at input is beyond the Abs Max rating of the device, many internal circuits including charge pump can get damaged. T

    2. This can lead to the IC not working as expected. Make sure the IC is always operated below Recommended Operating Conditions so that IC never fails.

    3. Adding Decoupling Capacitors at the input will help reduce the transient over voltage but you need to test on your board to check if the transient over voltage is within limits with caps added at the input. This is because the transient OV spikes occur due to parasitic inductance at the input which is purely a function of board layout. 

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Richard,

    Hope your query is solved. Please let us know if you have any other questions.