This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1278-SP: SYNC* and power-on

Part Number: ADS1278-SP

Hi,

For a single ADS1278-SP system, is it required to assert SYNC* after power on?

The specification states:

"For consistent performance, re-assert SYNC* after device power-on when data first appear."

If there is no assertion of SYNC*, what inconsistences in performance will there be?

The timing diagram in Figure 69 seems to imply that SYNC* can be asserted whether or not DRDY* is high or low, so that could be before data appears.

Just being careful, thanks!

rich

  • Hello Rich,

    Assertion of SYNC after power-up acts as a reset for the ADC.  There is an internal power-up reset circuit, but it will only work correctly if the power supply sequence is followed as shown in Figure 85.  DVDD supply needs to ramp first, followed by IOVDD (DVDD and IOVDD can also sequence together if the supplies are tied together), and finally AVDD.  The ramp on these supplies needs to be monotonic, with a consistent positive slope. 

    If you do not assert SYNC and the power-up sequence is not followed, the ADC can get into an invalid state and the output data will be incorrect, or there can be no output data (DRDY never asserts).

    If you assert SYNC after the supplies have ramped to the recommended values and data first appears (or a delay of 2^18 t-CLK periods plus 129 t-data periods), as suggested in the datasheet, then you do not need to strictly follow the power-up sequence, and the ADC will be much more robust to power supply issues during startup. 

    I suggest routing the SYNC pin and asserting it in your system for best consistent performance, as power-supply ramping in complex systems can be hard to predict, especially as other loads on the supply rails start-up and draw current with the potential to cause sags in the supplies during ramp.

    Regards,
    Keith Nicholas
    Precision ADC Applications