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Original question:

LM5022: LM5022 in SEPIC topology with adjustable output

LM5022: DC/DC based on LM5022 in SEPIC topology suddenly has stopped working

Tadeusz Tatery
Intellectual 310 points
Part Number: LM5022

Hello,

My DC/DC converter based on LM5022 in SEPIC topology suddenly has stopped working. Nothing is burned (at least I cannot see anything burned or bad smell). I've just switched converter OFF and ON again and after this no more usable voltage on output.

Currently voltages on LM5022 are:

Vin = 12,2V

RT = 1,98V

Vcc = 7V

FB = 2V

CS = 0V

OUT (pin 5) = 0V

ULVO = 1,67V

COMP = 0V

Voltage on DC/DC output is about 2V.

I've verified output transistor and diode, both are working fine. Please advice how to verify if LM5022 is burned or not.

This is my design:

  • 0
    TI__Mastermind 25520 points

    Hi Tadeusz,

    Thanks for considering the LM5022 in the design. 

    Can you take a picture of your board and test setup? Does your design not operate at any higher input voltages?

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Intellectual 310 points

    Hi Richard,

    I've also tried with 20V as Vin. I used this DC/DC for almost 5 months and tilt yesterday it worked fine.

    Please find below "picture" of my board (inductor is on bottom site, under U2).

    Thanks in advance for any suggestions.

    TT

  • 0 in reply to Tadeusz Tatery
    TI__Mastermind 25520 points

    Hi TT,

    I meant the actual PCB/hardware.

    From the results that you have given me, it does not seem that the IC is misbehaving. Your COMP voltage is 0V, and as such your duty cycle is also 0V as seen on pin 5. This follows the part behavior.  

    I think it is a little strange that your voltage seen at the FB pin is 2V instead of a lower voltage through the resistor divide, since your the output is also 2V. Can you check your output resistor divider and see if any components are loose, open circuited or shorted?

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Intellectual 310 points

    Hi Richard,

    You are right, R13 (in output resistor divider) had one pin not soldered properly (however it worked till yesterday). I didn't expect this place to be an error root cause.

    Many thanks,

    Tadeusz