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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?


  • Hello alexey,

    I guess (=do not know for sure) we do not show parallel examples as we have the dual LTC7802 in our portfolio which eases your desired app. Are you sure you need three phases for your output load? Please try LT7802 within LTPowerCAD and consider this part.

    kind regards


  • Hi Markus

    I need to build dc-dc with next requirements:

    Vin=12-28V, Vnom=24V


    It must be synchronized to the external clock 1MHz

    7803 was selected because of Fsw and 100% Duty cycle capable so it able to work down to 12V.

    Three phases in parallel provide required current with good enough efficiency.

    I would try LTC7802 but are you sure that LTPowerCAD supports it?

    I have the latest version and did not find it there.


  • Hello,

    the LTC7802 is not 100% similar to LTC7803 in all features ( for example 99% DC,max instead of 100% DCmax/PassThru),but the main behaviour is identical.

    In the LTC7803 datasheet you'll find an example with 12V@15A.
    In the LTC7802 datasheet you'll find an example with 12V@30A (two phases). Both example have same frequency, inductor, sense resistors and FETs selection. Even compensation values at pin ITH is equal.

    So for LTPowerCAD you can use the LTC7803 data and translate/copy for both phases of the LTC7802.
    I do not know if or when LTC7802 will be implemented in LTPowerCAD

    480W is quite challenging, maybe you have to double all  the FETs to spread the thermals on your board.

  • Hello,

    what I forgot: using 1MHz will be quite challenging as switching losses will be really high. For those kind of output power levels you should setup your system for best efficiency, hence smaller switching frequencies are the proper way to go. Yes, this means larger inductor and output capacitors, but the power level demands for a larger design anyway (thermals, double FET maybe...)

    kind regards


  • Markus,

    I know that and trying to find an optimal solution.

    By the way LTPowerCAD shows quite high efficiency at 1MHz for a single phase at 20A load.
    More than 98% and with two Top FETs in parallel the losses are in allowable range.

    Tks for you help.

Reply Children
  • 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


  • 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.



    LTC7802 12V@40A BUCK 500kHz

  • 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