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LTM4644 paralleling two modules with 8 phases 16x2=32A

Hello,

I am interested in using LTM4644 power module.
But I do not understand: is it possible to parallel two of them
to get 8 phase 32A power source for FPGA core supply ?

Datasheet states that "The phase of CLKOUT with respect to
CLKIN is set to 180 deg" so I can't connect CLKOUT of IC1 to CLKIN of IC2.

As I understand, the possible solution could be to use mcu or small fpga with two pwm or timer

each outputs 1 MHz square wave clock shifted 45 degrees between rising edges
(or 125 ns for T=1000 ns)

Could you suggest other solution ?


Best regards,
Igor Petrov,
FPGA Engeneer

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  • Hi Igor, 

    Yes, you can parallel 8 phases of the LTM4644 for up to 32A on a single rail. The reason for suggesting to interleave the phases when paralleling is mainly because it helps to reduce the total input and output rms currents and voltage ripples, it is not necessary for paralleling phases just recommended. With 4 phases already interleaved in the module the input and output ripples per module should already be very low, so whether you interleave the phases of the two modules (ie provide a 45 deg phase shift between modules) or not, the performance will be very similar. 

    You can just feed the CLKOUT of the 1st module to the CLKIN of the 2nd module, but if you have an external clock available with at least 2 outputs that are phase shifted (ie 0 deg, 180 deg is fine, clock such as LTC6908) it would be recommended to have each module have its own clock input signal. This would be recommended over feeding the CLKOUT of the 1st module to the CLKIN of the 2nd module since it minimizes jitter on the clock lines. 

    Thanks!

  • CAN I use two LTM4644 to make 32A ?  If yes,  need I  tie all FB, track,COM and Vout  pins together?  And need  I tie ClockOUT pin of first LTM4644 to  theClockIN pin  of the second LTM4644???ThankS

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