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LM2840: LM2840 short circuit protection? Vin = Vout after shorted output to ground

tee_user
Prodigy 170 points
Part Number: LM2840

Hello,

we use the lm2840 in our design. i try the short circuit protection.

i connect the output from the lm2840 (after the inductor) to ground for just a second.

the device is after that damaged and the vout voltage = vin voltage.

i think the integrated FET is shorted.

the regulator isnt working anymore.

thanks for the answer

greetings

We use the following parts:

  • 0
    TI__Mastermind 27470 points

    Hi

    pls monitor the input voltage and SW voltage see any over voltage happened when short happened. 

    and the layout is not good cause D2 GND is far away from C1 GND. 

    Thanks

    Daniel Li

  • 0 in reply to Daniel Li14
    Prodigy 170 points

    Hello,

    could be the bad layout the reason for killing the lm2840?

    thanks

  • 0 in reply to tee_user
    TI__Mastermind 27470 points

    Hu

    It is possible, if you have EVM, you can test it, it has OCP protection and can be safe used in short condtion.

    by the way, pls check the saturation current of inductor is higher than OCP value.

    Thanks

  • 0 in reply to Daniel Li14
    Prodigy 170 points

    Hello,

    thanks a lot for the answers

    Sorry for the question but what is the meaning of evm?

    I changed the defective LM2840 against an new one, and short the output with an 0,1R resistor.

    i ve attached the oscilloscope screenshot.

    Strange is that the device isnt dead after that test.

    I think the inductor isnt in saturation. I = 0,05V / 0,1Ohm = 0,5A

    Channel 1 is input voltage 24V

    Channel 2 is output voltage 5V, after scp is trigger on failing edge

  • 0 in reply to tee_user
    Prodigy 170 points

    Hello,

    after the result with the oscilloscope and the short with the 0,1 Resistor.

    i think about the difference at my first tests.

    the difference between the first tests and now was the ground connection.

    at the first tests i connect the ground with the micromatch, at the latetest test i sold an wire at the gnd layer.

    => i think the reason is the bad layout

  • 0 in reply to tee_user
    TI__Mastermind 27470 points

    Hi 

    one possible assumption is when you short close to output, the inductance between you output and short point as well as ground wire will be smaller than you short point is far.

    the inductance may resonant with output capacitor which will cause negative voltage on the chip's GND. this may cause the chip damage.

    EVM is board Ti officially provide for customer test the chip performance 

    Thanks

  • 0 in reply to Daniel Li14
    Prodigy 170 points

    Hello,

    i will change the layout from the board @ti example layout.

    But what is the meaning of EVM?

    Thanks

  • 0 in reply to tee_user
    TI__Mastermind 27470 points

    Hi:

    EVM= Evaluation Module 

  • 0 in reply to Daniel Li14
    Prodigy 170 points


    RE: LM2840: LM2840 short circuit protection? Vin = Vout after shorted output to ground

    Hi Daniel,

    great thanks for the answer.

    I changed the hole layout.

    is the new layout better in your opinion?

    Thanks a lot for the answer!

  • 0 in reply to tee_user
    TI__Mastermind 27470 points

    Hi

    the component placement is fine.but I will suggest you use direct connect to the power net especially SW, GND and Vin, VO instead of cross connection.  it can reduce the inductance of the net,

    and you can also move inductor close to the SW pin to reduce SW interference , it is a noise source.

    Thanks