Generate AVdd for Analog Chip (DAC)

[signalflow]

Hi, I am trying to use the AD5412 (DAC). It requires an analog supply voltage AVdd of between 10.8V and 40V. I was thinking about using a step-up boost regulator such as LT1316 to generate a 12V DC output to supply the AVdd pin with on the AD5412. I am worried about the noise though since it is a switching regulator. Will this be acceptable if I put decoupling caps between the AVdd to AVss pins.

Or is there a better way to generate this voltage? I have a 24VAC input with a rectifier and then a LM2596 switching regulator to convert down to 5V DC supply voltage from the 24VAC input. So I just have a 5V DC supply.

 

[barry]

If you've got 24VAC, you should be able to generate 12VDC from a linear regulator. Your basic question is way too broad to answer "will this be acceptable if I put decoupling caps...". What is the noise from your switching regulator? What does your board layout look like? (this is a BIG question). What is your required resolution? But you could possibly use a switcher with no problem. Add some inductors/ferrites.

 

[FvM]

If you just want to operate a DAC from low supply, use a 5 or 3.3v DAC. The special feature of AD5412 is the built in high voltage output for standard process signals (0-10V, 0-20 mA). So you'll use it when you want this kind of interface and then you need a high voltage supply.

A straightforward way would be to use 24V DC supply, as most automation interfaces do.

Stepping down from 24 VAC to 5V and up to12 V again sounds a bit strange. You'll also increase the power dissipation and generated noise of the step-down converter. But it's possible though, if you have reason to do so, go for it.

 

[signalflow]

I used an LM317 to generate a +24VDC supply for the DAC (needs 10.8V to 40V supply). I also have an ADC that needs an AVdd of 5V. My 5VDC supply is generated by an LM2596 simple switcher from 24VAC(rms) (34VDC after rectified), so it has some 150KHz noise on the line. I plan on using the 5VDC noisy output and putting some inductors after the simple switcher as Barry suggested before sending to ADC.