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Original question:

LM5145: Solution for multiple high power +24V outputs

LM5145: Evaluation module LM5145EVM-HD-20A

Hur
Intellectual 435 points
Part Number: LM5145
Other Parts Discussed in Thread: , CSD18563Q5A

Hi,

I am using the LM5145 chip for designing a 30V to 24V dc-dc converter with up to 12A current output requirement. I have the  LM5145EVM-HD-20A and am running some tests for evaluation. I have modified feedback voltage divider resistors to provide 24V output. The maximum current supplied at its output now is around 5.1A at 24V and does not go higher than that. Want to know that does the evm have any internal thermal or power limit? Also is there any other change required in the evm to get a higher output current?  Any help would appreciated.

Thanks,

Hur  

  • 0
    TI__Expert 4555 points

    Hi Hur,

    There is a chance that you might have lower Rilim resister and getting valley current limited. You can check your design with webbench design link that I created for you, I would recommend using this tool for future references as well.

    Best Regards,

    Ankit Gupta

    Application Engineer, Power Solutions

  • 0 in reply to Ankit Gupta95
    Intellectual 435 points

    Hi Ankit,

    The Rilim value in the evaluation board is 422 Ohms that is for 20A limit. I changed it to 576 Ohms as mentioned in the design on webench link but still the current is still limited to around 5 A.

    Thanks.

    Regards,

    Hur

  • 0 in reply to Hur
    TI__Expert 4555 points

    Hi Hur,

    Can you please share your schematics and PCB layout. 

    Best Regards,

    Ankit Gupta 

    Application Engineer

  • 0 in reply to Ankit Gupta95
    Intellectual 435 points

    Hi Ankit,

    I have the LM5145 evaluation board and am running some tests on it

    Regards,

    Hur

  • 0 in reply to Hur
    TI__Guru* 75832 points

    Hi Hur,

    Please use the LM5145 quicktart calculator (download it from the LM5145 product folder) to establish the correct component values, particularly for compensation. Note that the EVM is setup for a 5V output using 47uF/10V caps and a 220uF/10V electrolytic, so these will need to be replaced, e.g. with 10uF/50V ceramics. Also, the MOSFETs are currently 80V parts, so these could replaced with suitable 40V or 60V devices, eg. CSD18563Q5A.

    In terms of current limit, the Rdson of the low-side FET establishes a sense voltage. This is RC filtered by a 6ns time constant on the ILIM pin (to prevent negative voltage swings on ILIM). At high duty cycle, it is critical not to oversize this RC filter as it reduces the effective sensing time when the low-side FET is on.

    Regards,

    Tim