Power Sequencing

Hi Alexander1998 , 

Best practice when there is no known power seequence requirement is to power up the logic circuitry first (dvcc), then the analog afterwards (vdd/vss). having them at the same time is fine as well. It's also good practice to provide decoupling caps on all the supply pins even with no mention of it. 100nF should be enough to filter you high freq noise on the vref pin. Although I would advise to check the external reference's datasheet if you want to put bulk caps (1uF~10uF) on that line. 

Best regards,

Ian

Hi Ian,

thanks for your feedback.

Do VDD and VSS have to go up together or does the order not matter? What is the sequencing requirement for VREFIN?

What happens if the best practice is not followed? Is there for example an increased current consumption or can the device be damaged?

Regards, Alexander

Hi Alexander, 

For VDD and VSS, they should come up together. VREFIN could come up later than the analog and digital supplies. 

There may be issues with latching when the power sequence isn't followed. Increased current consumption is one effect. but in general, this is tested for our products, to make sure that any power sequence wouldn't result in latch-ups on the internal circuitry and that the DAC would not get damaged. The common occurrence for DACs is the initial output state uncertainty if the power sequence isn't followed. One example would be you'd get a full-scale output when you were expecting a zero-scale one. The risk would be on the adjoining circuitry on the DAC outputs if they aren't expecting this level of output during start-up. We've had that for other generics, tho I haven't seen one for the AD5721. 

Best regards,

Ian