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LMZ14201: I need a example circuit to drive safely EN from logic in 5 V DC

Part Number: LMZ14201

Hello

After one day without access to the forum due to server problem

I need if possible a example of circuit able to drive the EN pin of a LMZ14201 from a  logic level 0V / 5V DC

the floating level of the EN PIN is 6.5V when floating so I burn my logic component 5V

I am clearly lost and deeply lost as the doc say that logic level is 1.18 V so I do not to burn the LMZ14201  with 5 V

Thanks for your help

David

  • Hello David,

    The EN pin has internal clamp at 5V and a diode in series, so the pull-up voltage on the pin is actually less than 5V.

    Here is a diagram:

    You can also try a level shifter,similar to the one on your other post.

    Here is an example:

    Cheers,

    Denislav

  • Hello Denislav

    Thanks for your detail answer

    I have built a circuit as the PNP 3906 transistor for test but can you please confirm or explain this point

    Why the circuit is connected to the negative V out as this case is a negative generator , that do not look as normal if that a shifter normally the Volt source is positive as the En pin request a positive Voltage

    Regards

    David

  • Hi David,

    The application note above is actually for enabling the LMZ1420x when it is in inverting configuration. The -VOUT rail in that case is the return(GND) pin of the device.

    In your case perhaps you just need something like this:

    SYS_EN would be your logic signal driving a small N-ch MOSFET. 

    Let me know if this helps.

    Cheers, 
    Denislav

  • Hello, Denislav

    thanks for the Mosfet circuit

    one question : as the EN pin is floating but with a voltage due to internal conception of the LMZ , does that safe to ground it straight without a resistor ? when the TTL / Flag command is off

    so shall I add  a P channel to put the EN pin to the ground through a resistor when EN is OFF ?

    or

    shall I use a TC4428 if I connect to a twin N Mosfet as IRF731 I can get a compact solution by using one side will drive on the EN pin the other will ground the EN pin by using a resistor ?

    Regards

    David

  • Hi David,
    It should be OK to ground it without a resistor. The internal pull up current source is only 6uA.
    If you want to place a resistor, you can, but it will add another component.
    Cheers,
    Denislav
  • Hello, Denislav

    Ok I launch components order tomorrow and make tests
    I will publish circuit and results as LMZ is a useful components and driving them with logic level can allow broad range of application

    Regards

    David