LM5149-Q1: LM5149 OCP for short circuit

Yes, currentl limit should also protect from short circuits.

Send on a completed quickstart file so we can review your design (see the LM5149-Q1 product folder for the link).

100kΩ seems really high for the COMP resistance. Also, please ensure there is no noise on the CS signal.

--

Tim

For a variable VOUT, choose the compensation values at the max Vout setting (as this gives the lower effective ceramic Cout value). Then check the result at min VOUT with the updated Cout value as needed.

Also, check that you're using the correct effective Cout and ESR values with parallel electrolytic and ceramic caps.

Here is an Excel file to help with that:

Parallel Capacitors Zct LM3753-4 CEB Cin 4x300kHz.xls

The ESR is definitely not 1mΩ as entered in the quickstart calculator.

Also, note your inductor ripple current is really low here, 4%, mainly as Vin is so close to Vout. Try 10uH.

Try lower crossover frequency. Rcomp is quite high, as Cout is so high for this output voltage.

Hi Godziller,

I will close out this thread if there is no further activity. If you're still working on this, you can reply here. 

Regards,

Tim

Although it's a heavy load situation, no harm trying PFM, particularly if the current somehow goes negative. You can monitor the current waveform of each inductor, check for saturation, etc. Also, a hard short on the output can cause ground bounce, so check that you have multiple GND planes (a layer 2 GND plane under the power stage is critical).

--

Tim

Can you check what the inductor current and SW node voltage wavefroms.