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LM3880: I have a concern with EN pin LMZ12401H by using LM3880

Vincent David
Intellectual 340 points
Part Number: LM3880
Other Parts Discussed in Thread: LMZ14201, LMZ14203

Hello

I have now succeed to get the right flag sequence on my LM3880 thanks for the provided explanation.

I have another concern I try to command a LMZ14201 and 14202 , following the proposed schematic with the resistor divider

test result ( LM3880 is set with 100 K resistor ballast and works fine with LMZ connection )

LMZ14201 Vin is 12V

1) straight drive EN with a 5 V DC source that work

2) straight drive EN by using the LM3880 I destroy the LM3880

3) resistor divider  ( 9.1K / 20K ) EN by using LM3880 = I do not succeed to drive the LM14201 I measure 1.2 V out of the LM3880 after the ballast

does someone can explain where is the problem ?

Thanks

David

  • 0
    TI__Genius 13700 points

    It's not clear from your description what the problem is, also there is no LMZ12401, do you mean LMZ14201?

    I believe you are now referring to the EN pin of the LMZ14201 rather than the EN pin of the LM3880, correct?

    Can you attach some drawings of your setup?

    I did notice the below statement in the LMZ14201 datasheet, it isn't mentioned anywhere else and would seem to contradict the limit of 6.5V on the LMZ EN pin unless there is also an internal zener diode that limits the voltage.  It is not reflected in the LMZ block diagram or the pin description, we may need to query support for the LMZ to clarify.

  • 0 in reply to Brad
    Intellectual 340 points

    Hello

    it s look I have two subjects open on TI forum with the same question

    I don't understand at all how in the same doc

    1) EN pin can be pulled up to Vin level so 12V in my case

    2) EN pin max voltage shall be 6.5 V

    My problem is not solved at all

    Regards

    David

  • 0 in reply to Vincent David
    TI__Genius 13700 points

    I would disconnect the LM3880 from the LMZ and measure the LMZ Enable pin with 12V applied to VIN.

    If the LMZ Enable pin is pulled up to VIN internally, then I would expect that there is also an internal Zener diode that limits the voltage to <6.5V.

    If the LMZ Enable pin measures more than 5.3V then there is a problem.  Connecting it to the LM3880 FLAG1 pin will cause the ESD structure in the LM3880 to clamp the voltage to ~VCC + 0.3V and current will be drawn through the ESD structure which may be sufficient to damage the sequencer.

    I also posted an inquiry in the Power Modules forum for the LMZ14201, to ask if there truly is a pull-up/zener internal to the Enable pin, see link.

  • 0 in reply to Vincent David
    Intellectual 340 points

    Hello, Brad

    Thanks I check that and keep you informed

    in the LMZ14203 doc I have located this circuit I am in process to try as the LM3880 have an output of 5 V

    Regards

    David

  • 0 in reply to Vincent David
    Intellectual 340 points
    Hello Brad

    you are right with V in 12V I have 6 V V out and EN = 6 V so that destroy the LM3880

    Monday I will received the transistor to make a trial with th eTI provided circuit

    Regards

    David
  • 0 in reply to Vincent David
    Intellectual 340 points

    Hello , Brad

    I have design this circuit , normally that allow to

    put EN pin grounded when Flag is OFF

    put EN pin at +5V when when Flag is ON

    let me know what do you think about this

    Regards

    David

  • 0 in reply to Vincent David
    TI__Guru 58090 points
    David
    The same post was answered at e2e.ti.com/.../706398
    I will close this post.
    thanks
    yihe