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LM5145: Power management forum

Hedy Hung1
Intellectual 325 points
Part Number: LM5145
Other Parts Discussed in Thread: LM25145

Hi sir,

I used LM5145 to simulate 8-40Vin, 5Vout with 8A, and I found Boostrap cap is 0.1uF/ 25V, I though CBST voltage is equall to Vin, so CBST voltage rating should select 50V at least, should CBST be 25V or 50V?

Can CBST select 2.2uF or 4.7uF? what's the downside for this?

Any side effect if high Ciss NMOSFET be used?

 LM5145RGYR_WBDesign16.pdf

Thanks.

Hedy Hung

  • 0
    TI__Guru 73072 points

    Hi Hedy,

    Cbst voltage runs effectively at a voltage at VCC (7.5V) as it is charged when the SW voltage is pulled to GND. A 25V or 50V cap is fine. No need for a capacitance value above 100nF as it is harder to charge at startup. In general, the boot cap should be 1/10 of the VCC cap to prevent excessive VCC cap discharge at startup.

    Note the LM25145 also works here as it is rated to Vin-max of 42V. This is pin-to-pin with the LM5145. My recommendation is to check your design with the quickstart calculator (see product folder) and, if needed, send to me for review.

    Regards,

    Tim