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LM5155EVM-BST: Modification of EVM

Kenji Ohno1
Genius 5095 points
Part Number: LM5155EVM-BST

Hi Team,

My customer has experimented with modifying the EVM and has some problems.

Please advise for improvement.

 ・The input uses a stabilized power supply (33.6V / 30A), but the input current is limited to about 11A. Why not input more than 11A?

 ・ When trying to output 24V / 1.5A, the output voltage will be 20V.

I know the EVM specification is Min.6V. The resistance of UVLO setting is removed.

Also, to change the L value from 6.8uH to 2.8uH, 4.7uH (6.48mΩ, 11.7A) is inserted in parallel connection.

I would like to know the negative effects of parallel connection.

Please answer the following additional questions.

・Should I input to TP6 when applying VCC with an external power supply, or connect JP8 when connecting to BIAS?

・Changing the CS pin (slightly smaller than 8mΩ) improves efficiency. Is it necessary to adjust here while looking at the L constant and operation waveform?

・ Are there any concerns if the booster circuit is built at a later stage?

Best Regards,

Kenji

  • 0
    TI__Genius 17560 points

    Hi Kenji,

    The engineer responsible for this part is currently out of office. He will get back to you next week.

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Genius 5095 points

    Hi Richard,

    I am waiting for the return of the engineer.

    My customer reported that changing the inductor did not improve.

    I believed that changing the EVM UVLO setting and inductor value could achieve Vout24V/1.5A from Vin3.6V.

    However, it does not give good results.I would like advice for realizing it.

    I suspected Duty Limit and inductor saturation current, but the cause is not clear.

    I look forward to the answer along with the previous question.

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Mastermind 21720 points

    Hi Kenji,

    If you only change the inductor value it is likely that the circuit is running into peak current limit. This is implemented by the current sense resistor (R6).

    Please use the quick-start calculator to ensure that all the other component values are selected correctly based on the change in the inductor value. 

    http://www.ti.com/lit/zip/snvc224

    If you want to operate at low voltages the BIAS pin should be sourced from and external supply of the output voltage.

    Please let me know all the changes that have been made to the EVM.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Genius 5095 points

    Hi Garrett,

    Thank you for the advice.

    The value of Rs(R6) was also less than 8 mΩ, some improvement was seen.

    However, even if the Rs(R6) value is further reduced, the output value will not be the desired value.

    Can I send an e-mail directly? Because I receive a waveform from the customer.

    Best Regards,

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Mastermind 21720 points

    Kenji,

    I sent you a friend request. Please accept this and we can send messages back and forth so it is not posted publicly.

    Let me know if you have any questions.

    Thanks,

    Garrett