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I'm trying to convert 11-16 Vdc to 5 Vdc @ 3 A to run an array of low-impedance ratiometric sensors. The outputs are going either directly into an ADC or amplified through an instrument amplifier. Either way I need fairly low noise (<5mV).

To achive this I'm thinking about either using a switching supply to 6-7v and then a linear regulator or just a quality low noise switcher. The problem is I'm not a power guy and I don't really know what the best options in terms of parts for the switcher and linear regulator would be. Looking around a bit most high current linear regulators have pretty poor PSRR at switching frequencies.

What are good choices for ICs?

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I'd consider this part with an extra stage of LC output filtering: -

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I'd also consider adding 10nF (or whatever suits your bandwidth) capacitors on the ratiometric sensor outputs to ground to further reduce noise. Given that the outputs are ratiometric I'd also strongly consider measuring ratiometrically i.e. use Vcc as the reference for your ADCs - this cuts out a bunch of errors.

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