LM5146-Q1: Efficiency improvement

Hello,

Please send a completed quickstart calculator so we can review the power losses. Efficiency is low here, it should be 94%+.

Regards,

Tim

Hi Venkatesh,

Here are some comments on the quickstart file:

1. Inductor ripple current is 66% is high, causing high core loss (which is most evident in terms of efficiency impact at light loads, and especially with that high core loss Vishay inductor). Normal is 30-40% - try 10uH as recommended or, alternatively, increase Fsw to 200kHz and keep the 5.6uH.
2. Derate ceramic output capacitance for voltage and update the quickstart as needed (as this affects compensation values).
3. The high-side FET for a 48V-to-12V conversion does not need to be such low Rdson (as the duty cycle D = 25%). Better to use a higher Rdson FET for lower switching losses. This is important to optimize, as the high-side FET will be the hotspot in the design.
4. Enter 1Ω as an estimate for the internal gate resistance of the high-side FET

What is the FET part number here? Take a look at the 100V FETs used in the LM5146 EVM - use one increment lower Rdson based on the higher current level here. See Infineon and onsemi 100V 5 x 6mm FET portfolio for reference.

Regards,

Tim

Looks like a good low-side FET. You can go higher Rdson for the high-side FET.