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LM5155: Simulation quirks

Ryan.Bishop
Expert 3900 points
Part Number: LM5155

Hello,

I am trying to use the LM5155 in a SEPIC configuration (12V to 24V @ 3A).

Webench does not allow for SEPIC designs with this part, so I made a boost design, exported it to TINA, and then built my own SEPIC in TINA.

To avoid any mistakes, I simply copied this reference design to get started: http://www.ti.com/tool/PMP40488
(using only the positive output).

The design works for the most part, but I'm facing a few strange issues:

  1. When using the Nexperia FET from the design (model here and attached), I get this strange overshoot after soft start. Any way to resolve that?


  2. I wanted to make adjustments for higher current, so I tried putting some TI FETs instead of the Nexperia FET. This caused the simulation to never start switching, even with everything else the same. Any ideas what might be causing this?

I attached both TINA files for your reference, and here is a screenshot of the overshoot I mention in #1:

Working FET.TSCTI FET.TSCPMV213SN_25_04_2012.TSMPMV213SN_25_04_2012.lib

  • 0
    TI__Guru 73570 points

    Hi Ryan,

    Thank you for posting. The overshoot, if it is real but not the modeling issue, can be resolved by increasing the soft start capacitor.  

    I tried to run your models but it is so slow.  Please give us a call (myself or Eric Lee) and let's discuss in a con call, which may be more efficient.

    Thanks,

    Youhao Xi, Applications Engineering