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LMR62014: problems in boosting 12V to 16V

Mrunal Ahirrao6
Prodigy 50 points
Part Number: LMR62014

Hello all,

I am trying to boost voltage from 12 V to 16 V, but facing problems in it. Whenever I measure the output voltage it is 11.86(~12V). I am referring attached circuit. Why the circuit is not boosting?

webench_design_5126602_4_953226987.pdf

Below is FB pin waveform.

Below is inductor pin waveform before diode

  • 0
    TI__Intellectual 2655 points

    Hi Mrunal

      I have checked the Webench schematic, There is no obvious mistake.

    Did you do the simulation to found Vout=12V? or did a experiment to found it?

    Could you test the FB waveform and inductor current waveform？ It will be helpful for me to analyze it.

  • 0 in reply to Jing Ji
    Prodigy 50 points
    Hi Jing Ji,

    During simulation, the Vout was 16.4V. Now I have made a PCB using above circuit and now in hardware test its Vout=11.86V

    I will test the FB and inductor waveform and if possible upload screen shots of them.

    Thanks,
    Mrunal.
  • 0 in reply to Jing Ji
    Prodigy 50 points
    Hi Jing Ji,
    I have added the screen shots of oscilloscope. Please do check it.
  • 0 in reply to Mrunal Ahirrao6
    TI__Intellectual 2655 points

    Hi Mrunal

      Please check the value of FB divider resistors, Rfbt and Rfbb.

      I suspect you have soldered a wrong value.

  • 0 in reply to Jing Ji
    Prodigy 50 points
    Hi Jing Ji,

    I have checked the values of FB divider resistors they are correct. Except instead of 165K I have used 167K and according to datasheet the output voltage should be 16.44V but its 11.86V. Moreover the real waveforms don't match with simulated waveforms.
  • 0 in reply to Mrunal Ahirrao6
    TI__Intellectual 2655 points

    Hi Mrunal

      Because FB pin is connected with Vout through a divider resistor (Rfbt and Rfbb). The ratio of  VFB and Vout should be (Rfbt + Rfbb)/ Rfbb.

      First you can remove the Cf to check the FB and Vout voltage.

      Second double check the value of Rfbt and Rfbb. You can remove the resistors from the board and measure the value by DMM.

      The last way, you can change another IC, I am not sure the IC is good or not.

     

  • 0 in reply to Jing Ji
    Prodigy 50 points
    Hi Jing Ji,

    I have measured the FB and Vout voltage by removing Cf. And the ratio is correct.
    And I again soldered the Cf. Now strange thing happened, the SHDN pin was (as if) loading because the voltage on this pin was zero and suddenly after this strange thing the IC burned!

    I have replaced IC and other IC is also behaving same and will burn if kept in that way as it showed same symptoms before burning last time.

    What might have caused the IC to burn? and what is this happening with SHDN pin?
  • 0 in reply to Mrunal Ahirrao6
    TI__Intellectual 2655 points
    Hi Mrunal
    First remove Cf and solder a new IC, check the output is right or not.
    Because the Cf only influences stability, Cf doesn't have influence in SHDN. I suspect Cf is broken.
    If you remove Cf and the output is right, please change a new Cf to have a try.