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LM3880: concern to drive LMZ14201 EN pin voltage value

Part Number: LM3880
Other Parts Discussed in Thread: LMZ14202, , LMZ14201, LMZ14203

Hello

Thanks to Brad for reference LMZ mistake

I have another concern I try to command a LMZ14201 and LMZ14202 , following the proposed schematic with the resistor divider

 ( LM3880 is set with 100 K resistor ballast and works fine without LMZ connection )

LMZ14201 Vin is 12V

Test results

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

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

3) resistor divider  ( 9.1K / 20K ) LMZ 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

 

  • Is this what your circuit looks like, if not please provide a drawing of your setup.

    A drawing for each of the above conditions would help.

  • Hello Brad

    i use this one as I just need to drive the LMZ on flag 1 and the other LMZ on Flag 2

    When that work ( before to burn the LM3880 ) I have this signal traces on the oscilloscope ( I have select several voltage level to separate the tarces )

    Note : I just probe the Vout of the two LMZ I have no load connected , blue is the Ven LM3880

    Regards

    David

  • I'm going to go back to the datasheet statement I referenced in the previous post, shown again below, about the LMZ Enable pin being pulled-up internally.

    I suspect that the voltage on the FLAG pin is exceeding its maximum because it is being driven by the LMZ Enable.

    Look at the voltage on the FLAG pin compared to the VCC pin on the LM3880 when connected to the LMZ14201.

  • Hello, Brad

    Thanks

    I have check that , my flag voltage is 5 V as I feed Vcc of the LM3880 with 5V from a Lm7805 with decoupling caps

    following my understanding Voltage value En LMZ is 1.18 V typical and 6.5 V max

    IF the TI doc is right they say that EN pin is at Vin voltage ???? that look strange as they say in the same doc that EN max voltage is 6.5 V

    normally I am right by using 5 V

    when I power on the board in 12V ( both LM7805 and the two LMZ and LM3880 ) I have a peak of current that strange as nothing is connected to the LMZ output

    and I do not succeed to locate what is the current level of the EN pin on the LMZ perhaps the LM3880 is not enough in Amp or perhaps I shall set a inductor or use a transistor to protect the LM3880 ?

    Regards

    David

  • Hello , Brad

    I have located this circuit from LMZ14203 doc

    That sound to be solution as the logic flag ( LM3880 ) is protected from the LMZ14203 by using a transistor

    that sound logical I will test

    if someone have another idea I am open as I am really stuck

    Can TI staff confirm that this solution as copy and paste is OK for LMZ14201 and LMZ14301

  • Hi David,

    I think you have multiple posts in multiple forums regarding the same issue.

    Isn't this already addressed here:

    https://e2e.ti.com/support/power_management/powermodules/f/501/t/705209

    It would really help us if we keep the discussion in one forum in the same thread. Let's continue the conversation in the other thread.

    Cheers,

    Denislav

  • Hello Denislav

    ok , perhaps

    but I am still interesting to received help

    Regards

    David
  • Hi David

    I will close this post since the same question is also posted in the othe forum and Denislave will provide futher help on the LMZ14201.

    Regards
    Yihe
  • Hello Yide
    Great thanks to have closed the both posts
    I just still wait for a solution as I am still stuck
    I am extremely disappointed by the ''unclear'' LMZ14201 and the LM3880 documentation as that not really help for an easy and efficient design as I assess than logic command are in the 21th century something quite common as solution
    So I will re open a thread
    David
  • With the information from the previous posts that the LMZ14201 sources 6uA out the EN pin, limited at 6.5V. And knowing the turn-on threshold of the LMZ14201 is 1.25V max then a resistor to ground of at least 1.25V/6uA = 208Kohm is the minimum to turn on the LMZ14201.  And knowing your LM3880 VCC is 5V then the FLAG pins are limited to 5V+0.3V, a resistor to ground of no more than 5V+0.3V/6uA = 883Kohm is the maximum to prevent damage to the output stage of the LM3880.

    So any value between these two should allow operation of the LM3880 and LMZ14201 using the diagramed circuit below, I've shown a value of 250K for reference.

  • Hello Brad

    Thanks for your answer

    I will try the resistor to control the current

    Right now I have set a buffer by using a transistor ( 4401 ) I succeed to do not burn the LM3880 that nice but I have non consistent function I link oscilloscope screens pictures of the LMZ14201 output

    I have try 10K 20 K and 1K resistor I have the same anarchy

    Regards

    David