> I'm searching for a low noise switching supply IC. The goal is to 
> get
> +5V/200mA and -5V/200mA from a +3.3V with less than 5mV ripple. 
> Ideal
> one IC.
> Found so far: LT1534, MAX710, MAX735.
>
> Any good ideea appreciated.

To get low noise you probably want to think about either technology or 
filterability. Something with a continuous oscillation will help 
minimise the noise. Or going to something that runs at extremely high 
frequencies (some now in the low MHz region) will allow a fairly 
simple and small LC output filter to provide excellent performance. If 
absolute maximum efficiency is not essential then following with an 
LDO linear regulator (LP2950 or similar) should give you the best of 
both worlds.

I recently implemented a switching regulator design where the feedback 
was controlled by a transistor connected across the following linear 
regulator (emitter to input, base via resistor to output). This 
maintains the regulator drop at about 0.6v which is ample for a good 
LDO. At 5 volts this would reduce efficiency by a factor of 5/5.6 = 
0.89. This may be a bearable compromise.

By far the best LDO I have found recently in performance/$ and also 
very good in absolute terms is the AIC1722, which comes in several 
standard voltages. More on this superb IC anon. Hard to find outside 
Taiwan alas. If anyone knows a readily accessible source for the 
western world please advise.




            RM

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