TLC2578

Hi Naveen,

The TLC2578 splits is power rails between the analog and digital domains for a couple of reasons.  The first is due to the fact that the analog side of the chip needs a 5V source.  The allowable voltage range for the AVdd supply is from 4.75 to 5.5V.

A second reason is that many micro controllers - the MSP430 is but one example - have a 3.3V power requirement and cannot tolerate 5V being applied to their input pins.  Consider the consequences of tying the DVdd line to 5V in this example.  The /CS, SCLK and SDI from the 3.3V micro may be adequate to provide the minimum VIh, but the SDO from the ADC to the micro would be over the allowable input voltage level, possibly damaging the controller. 

A third reason is due to the nature of the actual power sources - more often than not, power supplies associated with the digital interface are noisy due to high speed logic.  Analog supplies are generally cleaner.  Having a clean supply on the analog side of the ADC helps to ensure better system performance and accuracy.  So to answer your first question, yes - if you have a 5V tolerant controller, you could conceivably tie the three voltage pins together and use one single supply.

For the second question, minor variations in the current or voltage on the power rails should not have an impact on the converted values for a given analog input.  This is going by the assumption that the variation is limited to the supply voltage range(s) noted in the datasheet on page 5 under the Power Supply section.  The reference on the other is another story.  If the reference voltage varies, your output code for a given input voltage will also vary.