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LM5176: Asking for the LM5176 OCP design suggestion

SHH
Mastermind 32326 points
Part Number: LM5176


Hi Sir,

 

My customer would like design LM5176 and use LM5176EVM for verification first due to customer’s LM5176 on customer PCB did not OCP correctly.

 

Would you please review question/waveform and provide your comment?

  1. Customer change LM5176 EVM R7 from 0.004ohm to 0.002 ohm and use E-load to increase the current.

However, the OCP seems not correctly response.

Vin = 20V , Vout = 27V

 demo board OCP R7=0.004ohm

demo board OCP R7=0.002ohm

 

 

 

 

BR,

SHH

  • 0
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. What components did the customer change on the EVM other than the sense resistor? The EVM is set to 12Vout, therefore I would guess that the feedback divider and the compensation were changed as well. Is the hiccup mode protection enabled now? Do you know if the customer tested the EVM also before modifying it? Can you please kindly ask to provide the scope plots of SW nodes and the CS pin too? I'm looking forward to hearing from you. 

    Kind regards, 

    EM 

  • 0 in reply to EM
    TI__Mastermind 32326 points

    Hi EM,

    thanks for feedback. Is there OCP tuning procedure for customer's reference?

    please refer to feedback from customer.

    What components did the customer change on the EVM other than the sense resistor?

    >>customer only change R14 to make surr in boost mode.

    Is the hiccup mode protection enabled now?

    >>yes. (1.38V>MODE<2.22V)

    No test waveform before modification

    Can you please kindly ask to provide the scope plots of SW nodes and the CS pin too?

    >> as below picture. 

    demo board r7=0.004ohm

    BR,

    SHH

  • 0 in reply to SHH
    TI__Genius 11215 points

    Hello, 

    Thanks for your feedback. Can you please repeat the measurements setting the bandwidth of your scope to 20 MHz for all the channels and minimising the ground loops when possible ?I would expect that a lot of noise is coming from the scope setup. I’m looking forward to your answer.

    Kind regards, 

    EM

  • 0 in reply to EM
    TI__Mastermind 32326 points

    Hello, 

    Thanks for your feedback. Can you please repeat the measurements setting the bandwidth of your scope to 20 MHz for all the channels and minimising the ground loops when possible ?I would expect that a lot of noise is coming from the scope setup. I’m looking forward to your answer.

    Kind regards, 

    EM

  • 0 in reply to SHH
    TI__Mastermind 32326 points

    Hi EM,

    customer do the measurement again with 20MHz bandwidth.

    Would you please review and provide your comment?

    7587.lm5176.zip

    BR,

    SHH

  • 0 in reply to SHH
    TI__Genius 11215 points

    Hello, 

    It seems like there is still noise in these measurements, what kind of probe has been used for these measurements? Do you know if the customer has the possibility to use the tip and barrel method? 

    Kind regards, 
    EM 

  • 0 in reply to EM
    TI__Mastermind 32326 points

    Hi EM,

    before getting the feedback from customer, what is the relationship for the measurement and OCP tuning?

    is OCP tuning by formula 23 and 24 in the datasheet?

    BR,

    SHH

  • +1 in reply to SHH
    TI__Genius 11215 points

    Hello, 

    As we are discussing this via email, I will now close this thread. 

    Kind regards, 

    EM