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LM2675: Extended SW to GND absolute maximum rating spec for <50ns

Kazuhiko Hirano
Genius 15098 points
Part Number: LM2675
Other Parts Discussed in Thread: LM2670, , TPS62400

Hello,

About SW to GND absolute maximum rating spec, LM2670 datasheet specifies not only dc voltage but also <50ns pulse as follows.

About LM2675, my customer would also like to know the extended SW to GND absolute maximum rating spec for <50ns.

Best regards,

K.Hirano

  • 0
    TI__Expert 5321 points

    Hi Hirano，

      Normally maximum value don't have a extended via transients. It was much more dangerous than the negative limit. SW voltage should always be lower than the maximum input limit. By the way, the datasheet on TI.com seems updated and is different from the picture you showed. Please check the newest datasheet.

    BR,

    Victor

  • 0 in reply to Victor Yu
    TI__Genius 15098 points

    BR,

    Thank you for your response.

    My customer is concerned of negative limit, not positive limit.
    Even if the datasheet specifies negative SW to GND voltage limit -0.3V, actual measurement results tend to exceed that.

    For example, though TPS62400 datasheet also specifies the minimum SW to GND voltage limit -0.3V, looking at Figure 38 – 41of the datasheet, it exceeds -0.3V and reaches ~5V.

    Do you have the extended negative SW to GND voltage limit for short pulses? Or do you have measured SW node waveforms with TI EVM to show it does not exceeds the -0.3V limit?

    Best regards

    K.Hirano

  • 0 in reply to Kazuhiko Hirano
    TI__Genius 15098 points

    BR,

    Let me correct one thing.
    Though TPS62400 datasheet also specifies the minimum SW to GND voltage limit -0.3V, looking at Figure 38 – 41of the datasheet, it exceeds -0.3V and reaches ~-1V, not ~5V.

    Best regards,

    K.Hirano

  • 0 in reply to Kazuhiko Hirano
    TI__Expert 5321 points

    Hi Hirano，

       1. Conclusion first: In my opinion, the negative spike is normally safe. I never saw a buck damaged because of normal negative transient spike before. So please convince your customer that a <5V transient is safe.

       2. Yes, many customer said they measured negative voltage<0.3V.  0.3V is the conducting voltage of parasitic diode. But for the transient spike here, it could be higher. We don't have a extend spike data because we can't test with all the different spikes.

       3. Please check if your customer using a ground ring to test the SW negative spike.  The following picture is test with 3inch GND line and ground ring. You can see the result is totally different. Test  setup is really important here.

    BR,

    Victor