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PTH08T250W bulk output capacitor selection with turbo trans enabled

Poul Knudsen
Prodigy 20 points
Other Parts Discussed in Thread: PTH08T250W

Hi,

I'm considering using 2 x PTH08T250W modules in load sharing mode, using the Turbo Trans function.

The target output voltage is 0.9V, the max. current approximately 50A, the dynamic current 50% of this and the max. allowed voltage deviation 45 mV.

In a non-Turbo Trans application, the total ESR for the capacitor bank needs to be more than 7 mOhm and the max. Cout less than 8000 uF.

Using the Turbo Trans function, the Cout is specified as the product of component capacitance and the component ESR. This product needs to be below 10000. No  maximum Cout and no minimum ESR is provided for the total bank in the specifications.

Does this actually means, that the PTH08T250W can accept a capacitor bank of i.e. 20 pieces of Kemet T520D687M004ATE012 (680 uF, 12 mOhm ESR, 4 V)  without becoming unstable or unable to start?

Are there any further concerns regarding Cout calculation when using load sharing between two modules?

Best Regards
Poul

BTW, the online TurboTrans SW seems to be out of order:

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  • 0
    TI__Mastermind 38230 points

     PTH08T250Wxx x2( parallel ) requiresa 45mV maximum 0.9V variation with transient response( 25Amp load step ) at maximum 50amp load

    Note I was not able to view the attachment.

    If the maximum load is 50Amps, the load step / transient is 25Amps, the each PTH08T250W with share in  the load step at 12.5Amps a. 12.5A x2=25A load step,

    1. Use Turbo trans Calculation  for single(1) PTH08T250W turbo trans data, 680uF 12 m Ω ESR at 4V, the load step per each module is 12.5A.

    a.  The total capacitance extracted  from  TT table B is 2500µF, (4 x680µF ESR12mΩ) = transient response 30mV( 12.5A column)  with  3.48kΩ turbo trans(TT) resistor on master only. The 4x680µF minimum output capacitance  is required  for each PTH08T250W to achieve 30mV transient response for 25A transient . 

    b.PTH08T250Wxx voltage tolerance calculation is with 1% Rset resistor tolerance 100ppm/°C temperature stability total is 1.5% maximum variation. If the  module temperature and line input voltage is stable, then the 0.9V output  voltage variation is about ±1% or ±10mV .

    c.. The  0.9V total output voltage variation is 40mV  with 30mV transient in this application ,TT resistor =3.48kΩ, minimum 2500µF (each PTH8T250W ) output capacitor  and 10MV voltage variation.

    My e-mail address is tguerin@ti.com if you have any additional questions on PTH08T250W.

    Tom