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Small signal open loop transfer function for dual interleaved bucks.

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T

treez

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Hello,
The LTspice simulation of a 28vin to 1V5 out, 20A out, Dual Buck converter (each buck switches at 200khz and is in CCM, current mode) shows a crossover frequency of 14000 Hertz and phase margin of 63 degrees.
The excel calculation of this circuit (also attached), gives it as 9600Hz for crossover, and 53 degrees for phase margin. –So slightly different result than the sim.
The excel calculation was done by simply assuming twice the switching frequency as each single buck stage (ie 400khz), and doubling the error amp transconductance as the two error amps are both connected at their outputs.
Do you agree that this is bona fide?...i mean, a full bridge smps is simply two interleaved two transistor forwards (2TF), and in that case you obviously double the switching frequency of the single stage 2TF for the full bridge……but in the full bridge you also double the duty, -but for the interleaved bucks, you do not, because each buck switches its own inductor.
So this is bona fide, yes?
We cannot afford the £10k for a AP300 to actually just measure it.

(pdf schem of dual buck also attached)
 

Attachments

  • Dual Buck _LTC3892 _28V to 1V5 at 10A (x2), 200kHz.zip
    4.9 MB · Views: 2
  • Dual Buck _LTC3892_28VIN to 1V5 at 20A _200KHZ.TXT
    10.4 KB · Views: 1
  • Schematic _Dual Buck _LTC3892_28VIN to 1V5.pdf
    21 KB · Views: 4
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