DC/DC converter for a 16-bit ADC board

Have you a link to a data sheet for the converter you are using?

Here it is:

No info on switching frequency. We decided not to use a similar AM radio transmitter @600 KHz. That's the main reason why we build it out of discrete.

It is generally a good idea to synchronize the DC/DC converter and the ADC clock to the same timing reference (as well as all other clocks in the system). This allows to filter out the noise. For example, if the DC/DC operating frequency is the integer multiple of the ADC sample rate, the noise will be converted to the constant DC offset, which is relatively easy to get rid off.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

LC filter it, input and output! Those cheap dc/dc bricks are very noisy.

How many bits of RMS noise are you seeing? For a fastish SAR adc, a few bits should be possible, low 10's being more practical.

John

In the datasheet, for a 5V input, it says that the switching frequency is typically 95KHz. My ADC clock sample rate is 10MHz. So the switching frequency is not an integer multiple of the ADC clock. Furthermore, this DC/DC is also not regulated. Should I switch to a switching regulator instead?

I was also confused about isolation with respect to DC/DC converters. My current DC/DC has isolation but I see many others that don't. Does isolation refer to the potential difference of the input versus the output or is it a method to isolate return paths for the input and output voltages (ie: digital voltage return paths and analog voltage return paths). In my case, does isolation matter or could I go either way.

If any information is needed to further understand my problem, I am more than happy to divulge.

Thanks, Aaron