Understanding DAC specs

Question

I am confused on how the specs of a DAC work together.

I am looking at this one: http://www.ti.com/lit/ds/symlink/dac7811.pdf for a project and am wondering how the sampling rate (5 MSPS), the serial clock rate (50 MHz) and the resolution (12bits) all work together.

Where I'm getting lost is how the resolution and the sampling frequency work together. If my fs is 5 MHz, does this mean that I have 12 bits to represent 5M worth of values? Or does each single sample in the 5 M samples have a possible value from -=2^12?

This particular DAC has a 16 bit register with the first 4 being control registers, so what exactly goes into the last 12? They're binary values, so how can that accurately represent a signal being sampled at 5 MSPS? I know that the clock can operate at a max of 50MHz, which is how fast the DAC can send packages back and forth from my micro-controller. Does this value have anything to do with sampling rate or resolution?

I've been all over google and wikipedia for this and have checked with other students who aren't quite sure either. Can anyone offer clarification?

Edit to add: here is the link to the Newark.com page for this part where it specified 5 MSPS http://www.newark.com/texas-instruments/dac7811idgsr/digital-to-analog-converter-dac/dp/85K0568

Answer 1

Each sample is 12 bits, giving one of 4096 possible values. There are 4 additional bits attached to each sample for control purposes.

With an input clock rate of 50 MHz, that means the maximum sample rate isn't 5 MHz, (I don't know where you got that from) but 50MHz/16 = 3.125MHz.

And your MCU needs to feed it at that rate : 16 bits, 3.125 million times per second, if you want to achieve that sample rate. It's perfectly OK to run it at a lower rate, of course. There are 2 ways to do that : either use a slower clock on the SPI interface, or by only asserting SYNC less often.

Answer 2

DAC stands for Digital-to-Analog Converter. As the name implies, your system pushes a digital value into the converter, and the converter produces analog signal with DC amplitude proportional to the digital code. The DAC takes 12 bit of data, no more.

How it works together?

1. This particular DAC takes digital data in serialized format, it is a low pin count IC. The serial interface runs at 50MHz clock.
2. Your MCU must have the corresponding converter to supply the serial stream of data, in format described in DAC's specification;
3. The format of data is FIXED at 16bit, where the low 12 are actual data, and 4 are some service data. Each time the MCU must send new 16-bit serial packet, the DAC will output new DC analog value. The DAC does not send any data back.
4. How fast the DAC can operate (change output)? The transmission of the 16-bit control world of data takes about 20 interface clocks, according to the spec diagram. It means that it takes 20 * 20ns = 400 ns to output new value at DAC's output. This means that the output signal cannot be updated faster than 2.5 MS/s.