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LMR14030-Q1: lmr14030-q1 short to GND

user4370495
Expert 1155 points
Part Number: LMR14030-Q1
Other Parts Discussed in Thread: LM2735-Q1, LMR14030, LM2735

Dear TI experts:
      The customer system has two levels of power. The first stage power supply is 12V to 3.3V, which supplies power to the system.
The second stage power supply is 3.3V to 9V, which supplies power to the external camera module.
12v---->3.3v use lmr14030-Q1, 3.3V--->9V use lm2735-q1.

if customer put the 9v power short to GND through wire on purpose,  the lm2735-q1 output voltage change to 2.98v,
and the lmr14030q1 output voltage still be 3.3v, but the 12V input current change  from 0.14A to 1.05A.
------I think,lmr14030q1 and lm2735q1 are all go into cycle-by-cycle current limiting current protect mode. however lmr14030q1 current limit is 5.5A(Typital), 7.7A(MAX.)
So, the input current increased and output voltage still keep the same. ------- Is my understanding correct?

if my custom want no output when 9v power short to GND through wire, How to optimize the circuit to achieve this function? thanks very much.

schematic1:

  • 0
    TI__Mastermind 23815 points

    Hi,

    I believe your  understanding is correct. You might have to have a disconnect switch maybe to make sure that the output is disconnected. 

    The boost converter in general during a short circuit condition at the output, the VIN will charge the inductor L16

  • 0 in reply to Arief Hernadi
    Expert 1155 points

    Dear :

    you mean to add external disconnect switch to cut off the power?
    if the short condition continues,lmr14030q1 will go to frequency fold-back to protect mode,  and more time for the inductor current to ramp down and leads to a lower average inductor current.
    But cause 3.3v normal output , L16 & D10 still work ,it maybe demand this two parts (before lmr14030q1 goto Thermal Shutdown protect).
    custom think it will be a big risk,  any advise can help me to get rid of the risk.
    thanks.

  • 0 in reply to user4370495
    TI__Mastermind 23815 points

    Hi,

    I think when the LMR14030 goes into current limit, the frequency will foldback as you mentioned.

    As the boost converter is shorted the VOUT of LMR14030 should collapse down unless there is resistance in between the output of LMR14030 and the input of LM2735.

    You can try to perform an over current test on the LMR14030 and you should see the output voltage of LMR14030 starts collapsing.

    Do you have any oscilloscope waveform of the short at the 9V?

    If you want to be sure, I still think you might require a disconnect switch to cut off the output power

    Here is one sample design for boost that uses disconnect switch

    https://www.ti.com/lit/ug/tidubu0/tidubu0.pdf

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    TI__Mastermind 28770 points

    I assume that this issue is resolved. If not , please start a new thread and we will get back to you with an answer.

    Thank you.