LTC7803 parallel operation

Hi there

could LTC7803 be paralleled? Nothing described in the datasheet.

LTpowerCAD allows to make it.

I would use three parts in parallel to work on common load.

Question is how to sync it from the external clock and make the phase shift between the output phases?

Alexey

  • Hello Alexey,

    I don't want to blame LTpowerCAD, because it's a wonderful and powerful tool, but 98% at 1MHz switching frequency does look too optimistic  to me. So I guess your selected externals might not be completely modeled or some sources of power losses are missing. Please sent your design file for a cross check.
    A rough input end up with 97% for 1MHz and 98% at 500kHz (changed inductor for sure). Expect less efficiency in real life. The DC of approx 50% is good for higher efficiency, but with 480W and 97% you still  have a circuit with nearly 15W of losses in the FETs and the inductors

    kind regards

    Markus

  • Hi Markus,

    it looks too optimistic to me too. Therefore I reduced the Fsw down to 500kHz.

    The design file is attached.

    Any comments/suggestions are welcome.

    Regards,

    Alexey

    LTC7802 12V@40A BUCK 500kHz 2phases.zip

  • Hello Alexey,

    you have chosen an inductor where no AC losses are listed in the library. The SPR1245A type has an IR rating of 28A, which is too small, resp. would lead to a very large increase in temperature. You should focus on the recommended parts from the inductor list (in bold letter). Maybe XAL1010 from Coilcraft
    The Vishay control FET is not the best in terms of losses according to the tool. Some Infineon parts are listed with better performance.
    Beside the external conmponents a good layout is vital for those pwoer levels, check datasheet recommendations and design data from evalkit. Reserve enough pcb space for good thermals.

    kind regards

    Markus