LM27313: Switch Current - leading-edge blanking integrated or not?

Part Number: LM27313

Tool/software:

Hello,

I need a new Booster Design to Boost 5V to 12V. I simulated the LM27313 in WEBENCH Power Designer.

All seems ok but if I looked to the Iswitch Waveform I was surprised that there are current spikes up to 6A-7A. The spike has a short time under 1µs and is highest in state of no load (idle).

The spikes may come from the capacitance of the integrated FET on the Drain connection!?

My question: Is the functionality given or switch the current limiter to an error? Does the high current damage/destroy the integrated components?

In other words, Does the LM27313 have leading-edge blanking integrated?

Thanks for your help.

Best regards

Jochen

  • Hi Jochen,

    Could you send me the detailed work conditions for the WEBENCH simulation that the high switch current was observed?

    I'd like to regenerate the abnormal simulation first and then check the reasons.

    Regards

    Lei 

  • Hi Lei,

    subsequent the detailed WEBENCH report. I hope you can see it.
    I changed some components ("choose alternative") but all are alternatives from the WEBENCH tool, because not all components are downloadable at the Altium Manufacturer Part Search.

    6735.WBDesign3.pdf

    Thanks for your help.

    Regards

    Jochen

  • Hi Jochen,

    I'll check and reply to you tomorrow.

    Regards

    Lei

  • Hi Jochen,

     5V to 12V @0.25A is a very typical work condition. The big current you observed should be caused by improper simulation setup.

    Sorry I didn't re-generate on WEBENCH. Could you send you simulation results or screenshot to me?  

    And one more confirmation, the "Iswitch" refers to the inductor current, right? Please correct if I have wrong understandings.

    Regards

    Lei

  • Hello Lei,

    in the attached dokument "6735.WBDesign3.pdf" above on page 8 you can see the diagramm of ISwitch. This is the currrent which flow through the internal FET. It's not the Inductor current. The Inductor Current is shown on page 7 IInductor diagramm, it looks good. hereinafter the waveform of ISwitch in detail:

    hereinafter the Link to the simulation model:

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=EAB91EAF91C1BC94

    The peak current is very low in time but the question is, will the internal components damaged? And does this high current went to an error state because of the internal current meauserement?

    Thanks for your help

    Regards

    Jochen

  • Hi Jochen,

    Thanks for your information.

    The high current of Iswitch you observed is caused by the diode, for which the minority carriers sored in the forward should be cleaned before reverse-biased. So there will be a additional current into the low-side FET. 

    In the actual conditions, there will be tens or hundreds of Rdson (I think in the WEBENCH mode this Rdson may be very small), so the Iswitch will be much smaller than the value you observed. And the duration is very short. So there are no concerns for this current.

    And also, when Schottky diode is used, this current will be even smaller.

    Regards

    Lei