LM2678-ADJ heats up @ 4amp

Hi Andreson,

The part cannot do 16V to 13.7V. The part is capable of only 91% duty cycle and you are exceeding that once you factor in the efficiency.

Please use Webench to generate a design with a part that works or increase your input voltage by a volt or two or conversely decrease Vout by a few hundred mV's.

Also Typically we like to use a 4.5A diode for a 4A application, gives better efficiency and can handle corner cases better.

Finally, please remember for a buck converter, your input current can't exceed load current.

But in this case, you are exceeding maximum duty cycle. 

Thanks,

Anston

Andreson, The duty cycle maximum and minimum are intentionally best case. This allows us to divide the reference duty cycle in the datasheet with expected IC efficiency to specify an operating voltage. In your case, this IC can ideally operate in the duty cycle range of 0% to 91%. Divide your calculated duty cycle which is .85 by 90% efficiency. Your duty cycle comes out to be a little over 91%. Hence not possible to do 16Vinto 13.7Vout. You Have to reduce output or increase input. Hope this helps! Thanks,Anston