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LM25149: LM25149 change output and switching frequency

yx yan
Prodigy 160 points
Part Number: LM25149
Other Parts Discussed in Thread: , LM5143, TINA-TI

When I use LM25149EVM board,I change output voltage to 25.2V(by change R20 and R21).

EVM board works good,but L3 is hot when loading 6A(temperature of L3 >100℃，ambient temperature is 25℃).

Then I chang switching Frequency to 500kHz(by changing R13 to 42K),when power up,it looks good,but there is a noise sound.

After 3 seconds,board shutdown,Q1 and Q2 burned.

Two Questions:

Why Q1 and Q2 burned?

And I want to simulate LM25149 Loop stability(gain margin and phase margin),how to simulate?

  • 0
    TI__Expert 7940 points

    Hi,

    LM25149EVM is designed to work at 2.1MHz, and the Vout=5V. Switching frequency will affect multiple component parameters such as inductance value and loop compensation. In addition, the withstand voltage range of the output capacitor on the EVM is only 10V. Exceeding the withstand voltage may cause damage to the output voltage and burn the chip and Mosfet.

    It is recommended that you use the calculation tools on the official website to check the parameters of the components on the EVM board. The link is shown below. At the same time, please pay attention to check the withstand voltage value of the capacitor. You can find the Bom used by the EVM in the LM25149-Q1 EVM User's Guide. 

    https://www.ti.com/tool/LM5149-LM25149DESIGN-CALC 

    What's more, if you want to simulate LM25149 loop stability, you can also use calculation tools. Thanks.

    Aurora

  • 0 in reply to Aurora Tie
    Prodigy 160 points

    Is every buck componet have its calculation tool?

    For instance,LM5143?

    If one buck do not has its calculation tool,how can I simulate its loop stability?

    Thanks

  • 0 in reply to yx yan
    TI__Expert 7940 points

    Hi,

    Basically all controllers have calculation tools (include LM5143). The selection of compensation parameters is explained in the datasheet. Customers can also calculate by themselves.

    You can also do loop tests or simulate using pspice models. The pspice model can also be downloaded from the official website. But the loop test part needs to be built by yourself. Thanks.

    Aurora

  • 0 in reply to Aurora Tie
    Prodigy 160 points

    Can I do loop simulation by using TINA-TI?

    Thanks!

  • 0 in reply to yx yan
    TI__Expert 7940 points

    Hi,

    If the official website has a corresponding model, it can be simulated. But if not, you may need to build the model yourself. Using existing calculation tools may be the most convenient method. Thanks

    Aurora