Can I assume that if I use the layout shown in the data sheet that
I'll be relatively safe from EMI? In terms of changing to a lower
frequency switcher I'd really prefer to use a fast switcher in this
case to keep size and weight down. Every gram counts in this
application.

Thanks,
Zik

On 9/5/06, David VanHorn <dvanhorn@microbrix.com> wrote:
> In my experience, the simple switchers are pretty noisy.
> They are designed to be easy.
>
> dVdT control is a big thing, a switch that turns on very fast can have
> oscillations due to inductance in it's emitter/source lead. Turning off
> quickly causes overshoot and ringing on that side, and just fundamentally
> speaking, a fast edge has lots of harmonics.   Slowing down the turn on and
> turn off costs heat in the switch, and efficiency, but it lowers the amount
> of harmonics generated, and lowers/eliminates any oscillation or ringing.
>
> I disagree with the need for multilayer boards, I rarely use them.  I am
> very careful about pcb layout, always returning current to it's source.   A
> sloppily routed multilayer board is always quieter than a sloppily routed
> two layer board, and I suppose the extra layers are always helpful, but when
> I'm achieving noise levels that cause the part 15 test engineer to ask me if
> I'm sure that the device is on, I think that adding extra shielding is just
> adding extra cost.
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