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

  • 0
    •  Analog Employees 
    on Jan 28, 2021 4:41 PM

    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

    Markus

  • Hi Markus

    I need to build dc-dc with next requirements:

    Vin=12-28V, Vnom=24V

    Vout=12V@40A

    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.

    Alexey

  • 0
    •  Analog Employees 
    on Jan 29, 2021 9:37 AM in reply to alexey.kolesnyk

    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.

  • 0
    •  Analog Employees 
    on Jan 29, 2021 4:35 PM in reply to MarkusHP

    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

  • 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.