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[SOLVED] switching regulator for analog circuit

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seyyah

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I'll power an analog circuit from 24V and the supply is 5V. I need to use a switching regulator. What do you suggest me to prevent switching noise coupled into analog circuit? Thanks
 

crutschow

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Are you going to buy or build the regulator?

Several years ago I designed a 15V to 5V 1A switching regulator with less than 12µV of output noise. Here are some of the steps I did to achieve that:

1. A careful layout with minimum path-lengths for all high current traces on a PCB with decoupling of all chips power pins directly to a ground plane or flooded ground planes on the other layers.

2. Common-mode choke on the input.

3. Oversized output LC filter to minimize ripple

4. Additional LC filter on the output.

5. Regulator mounted in an EMI sealed metal housing with EMI filter feed-throughs for all input and output wires.

You likely won't have to do all those things for typical analog requirements, but with the above I was able to meet the noise requirements measured at the output.
 

seyyah

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I will buy, not design, thanks for the tips. Which type should i buy i probably go 12V from 24V and then go 5V from there with a linear regaulator.
 

seyyah

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Ok, should i go with high switching frequency or low? Are there any differences between simple switchers and the one with more sophisticated like feedforward and strict regulation control, does it differ to use voltage control ones or current control ones, etc...?
 

HTA

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Many questions at once. These can only be answered when the specification is more in detailed. Each of the different DC/DC converter types has his specific advantage/disadvantage for specific operation conditions. Maybe you can use this online tool: http://www.ti.com/ww/en/simple_switcher_dc_dc_converters/power_module.html to select a DC/DC converter. If the ripple performance is not enough you still could use an LDO to supply the analog circuits. Keeping digital switching noise away from the analog part is the key target for the PCB layout. Here you find some basis of the different types of DC/DC converter and regulator: http://www.ti.com/lit/an/snva559/snva559.pdf .

Enjoy your design work!
 

pilko

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@ HTA I have been lurking with interest. --- you quoted "If you have analog an digital parts it is best to have a split design with DC/DC-converter followed by a linear regulator. One example of such a DC/DC converter for sensor supply is http://eetimes.com/design/power-mana...gital-supplies ."
After much Googling,I cannot find an example of this or any other chip incorporating both a switching reg and a linear reg on a single chip.--- do you have any info?

Regards

pilko
 

pilko

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Thanks HTA, I did more searching and finally found a supplier. (I didn't expect the chip to be just named iC-WD)

pilko
 

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