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

Question asked by doctormord on Aug 12, 2018
Latest reply on Aug 14, 2018 by GPerica

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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