Hi,
For the past few months, we have been experimenting with the ADS8555 with good results. We particularly like the 1.2uS conversion time.
We recently started evaluating the ADS8568. This appears to be nearly identical to the 8555 but providing an extra two channels. However, the cost of the extra two
channels is a slower conversion clock, leading to longer conversion times.
With the built-in conversion clock, what we are seeing with the ADS8568 are conversion times ranging from 1.5uS to 1.58uS, not 1.7uS as the datasheet says. Sure the datasheet specs a maximum of 1.7uS, but at 1.58 microseconds, we calculate that the internal conversion clock must be running faster than the 11.75MHz maximum for the external conversion clock.
Up until now, all of our experiments have been done using the internal conversion clock, but we will soon do experiments where we supply our own external conversion clock.
Given our observations, and also a desire to have conversions finish as quickly as possible, we have the following questions:
1. What are the risks with exceeding the 11.75MHz maximum external conversion clock frequency specified on the data sheet? On the ADS8555, the external conversion clock is up to 20MHz. Is it a matter of more heat inside the ADS8568 due to more converters? For what it's worth, our sample clock is currently 160kHz.
1a. Is it possible that the 11.75MHz could be exceeded if we are not operating the converter at its maximum sample rate?
2. With another company's converter, we noticed that if we operated with a slower conversion clock, the converter was less noisy. Already we are very impressed with the low noise qualities of the ADS8555 and ADS8568, but we are wondering if there are benefits to operating at a lower external conversion clock. Please advise.
Thank you,
Marc
