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AD7327 power sequence for VCC and VDD

Question asked by ArrowJarret on Sep 3, 2015
Latest reply on Sep 20, 2015 by KarenNE

Looking at the datasheet for the AD7327, in Table 4 the Absolute Max Rating (AMR) from VDD to VCC is listed as (VCC-0.3V) to 16.5V. By this spec, the power sequence needs to bring up VDD before VCC so that there are no violations during power up. For example if VCC comes up first and VCC=5V while VDD=0V then there is a -5V difference which is less than the AMR spec. Reversing the power up sequence so that VDD=12V and VCC=0V then the +12V difference is within AMR spec.

http://www.analog.com/media/en/technical-documentation/data-sheets/AD7327.pdf

 

However, the evaluation board has set the sequencing so that VCC comes up first in the sequence and VDD follows (Figure 27, schematic page 2 in eval board User Guide).

http://www.analog.com/media/en/technical-documentation/user-guides/UG-419.pdf

 

So my question is which is correct and what does ADI actually recommend for sequencing to avoid violating the AMR spec.

 

Thanks!

 

Jarret

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