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LTC3784 (LTC3787)- 1200W 4 phase FCC design - Hot inductors while idling, no load connected

Hi Linear-Staff,

we designed a 4-phase layout with the LTC3874 in a 2/4 phase arrangement. Everything seems to perform like expected but the inductors getting really hot when using FCC with no load connected.

The design is made with the following specs:

fsw: 230kHz

FET/Sync: Toshiba TPH2R506PL

inductors: Coilcraft XAL1580 3uH

DCR sensing

VIN: 10-45V

VOUT: 51V

IOUTmax: 23A

POUTmax: 1200W

Using Burst-Mode or Pulse-Skip of course wont heat up the inductors. Any hint? I can't see any frequency-jitter, compensation seems to work fine as well (with rather low bandwidth of roughly 4kHz (70+dB PM) at 10V VIN). The loop compensation is design made with LTPowerCAD.

Iripple is about 13A per phase at VIN=10V, shouldn't be an issue for the inductors.

I haven't spoken to my local FAE as this is a proof of concept student project which may go into production in the future. (No time to market yet)

Any ideas?

Best regards, Christian

www.360customs.de - www.stromrichter.org

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  • Hi Christian:

    The XAL series has high core losses. That may be OK in some applications but it will result in higher temperature rise in your application.

    The inductors types specified in our data sheets and used on our demo boards have all been selected for low core and DCR loss.

    You can use LTC3784 in place of LTC3787 if you would like pulse skip mode in 4-phase design. The OV pin will allow the 3784 to run in pulse skip mode.

    BR,

    Goran

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  • Hi Christian:

    The XAL series has high core losses. That may be OK in some applications but it will result in higher temperature rise in your application.

    The inductors types specified in our data sheets and used on our demo boards have all been selected for low core and DCR loss.

    You can use LTC3784 in place of LTC3787 if you would like pulse skip mode in 4-phase design. The OV pin will allow the 3784 to run in pulse skip mode.

    BR,

    Goran

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