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  • TI Thinks Resolved

LM27222, What to do with LEN?

Prodigy 55 points

Replies: 7

Views: 930

The data sheet for the LM27222 is not clear on what to do with LEN pin. It shows it going the the PWM "controller".  Can I just tie this to +5V? That is how I have it now and it kinda works, but the MOSFETS get warm. Thoughts?

  • Is there any other way to get technical support from ti?

  • In reply to Jeramy Hughes:

    Hi Jeremy,

    Let me find the correct apps engineer to support your question.

    Regards

    Peter

  • In reply to Peter Meaney:

    Peter, any luck tracking down the right apps engineer? I'm starting to think I should just use a different chip because I can't seem to get an answer.
  • In reply to Jeramy Hughes:

    Hi Jeramy,

    Sorry no feedback yet. Looking at the datasheet the LEN should be pulled high and then the mosfets will follow the IN signal. Depending on the power been processed it is normal for the fets to get warm.

    Take a look at the gate drive signal for the low side fet and the drain of the low side fet. they should be in sync.

    Regards

    Peter

  • Hi Jeramy,

    Sorry about the delayed response. This post slipped through the crack. 

    Both LEN and IN are active high and are internally pulled down to gnd. The LEN is intended to avoid false LS switch turn ON. Fig 4 shows how the LEN can force the LG OFF when intended. LEN is part of shoot-though protection that LM27222 offers which can hold the LG off for 170ns, beginning from the instant when IN (HG) goes high. Keeping the LEN floating or high at all time is possible depending upon the application. 

    If you are keeping the LEN at 5V all the time, it shoudn't cause FET over heating. How much current are you drawing through the FETs? Can you share a schematic or gate switching waveforms?

    Kaisar Ali

  • In reply to Kaisar Ali:

    Hi Kaisar,
    Is it possible to contact you offline to discuss this?
    Thanks,
    Jeramy
  • In reply to Jeramy Hughes:

    Sure Jeramy. I can PM you my contact information.

    Kaisar Ali

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