ADC1246/7/8 clock source

Marco,

There was some initial testing with the EVM using an external clock, but we did not see any significant difference.  We left the provision for an oscillator on the EVM for customer testing purposes.  We are able to achieve excellent datasheet performance using the internal clock.  Having said that, there is some variation from lot to lot of the clock frequency and it can range from 3.89 to 4.3 MHz.  So if you either want to tweak the modulator rate, or have a more precise clock you may want to use an external device.  If you do use an external clock, make sure that it is a good, clean and very low jitter clock.  You can definitely make things worse with a poor external clock, primarily an increase in noise.

So, most applications will work very well using the internal clock.  If you want to verify or experiment, I would suggest getting one of the EVM kits and install an oscillator on the board.  If you get one of the ADS124XEVM-PDK kits (substitute the X with a 6, 7 or 8 for the desired device kit), you can compare the performance using our ADCPro software.

Best regards,

Bob B