Thanks Roman and Matt,

I'll experiment with the chip when it'll be available=20
to me. It seems I could reach 80-90% efficiency=20
at 10khz (1:100). For a start I'll put open drains=20
with resistors in place of a digital potentiometer.

   Mike.

> Mike Singer wrote:
> >  Has anybody any suggestions of max regulated frequency?
> > If I replace bottom resistor of feedback chain by digital
> > potentiometer and reduce output capacitor, what "max
> > frequency" very aprox could I send to digital potentiometer,
> > aiming at microstepping motor applications?
> > LM3485 can work at >1mhz.

Roman Black wrote:
> A good rule for PWM is 10:1. So if your PWM freq is
> 1MHz, (as above) you should not try to accurately
> simulate changing waveforms over 100kHz. Even 10 PWM
> cycles will cause significant ripple as you can't use
> large filter caps. 50:1 is better.
> -Roman

Matt Pobursky wrote:
> Check the frequency response specification of the digital pot. If I
> recall correctly (and I haven't looked recently), most digital pots
> don't have a frequency response much above a few 100KHz.=20
> Also, check on
> the settling time from when you give a digital control input until the
> pot value settles to it's final value. I think these parameters are
> going to be your limiting factors concerning speed.
>=20
> A better way to do it might be to use a D/A converter in the PS
> feedback loop if you want to adjust output voltage/current at a fast
> rate.

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