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ADS7955 - power up sequencing

Daniel Siroky1
Prodigy 135 points
Other Parts Discussed in Thread: ADS7955

Hi E2E,

I have quick questions to the ADS7955SDBT converter :

1. For pins 15 and 16 the datasheet says "Pins internally not connected, do not float these pins". What should I do with them - connect to ground? Anyway why, as they are not internally connected?

 2. I will use +5V for analog power supply +VA and +3.3V for digital I/O supply+VBD. Is there any requirement for power supply timing or sequencing during switching on?

 Thank you

Daniel

  • 0
    TI__Guru 55026 points

    Hi Daniel,

    The ADS7955 (8ch) TSSOP device pin out is compatible with the other ADS79xx devices in the family (12ch and 16ch versions). These pins correspond to the unused channels and are not connected internally.  The recommendation is to tie these pins to AGND to avoid any potential cross talk issue.

    There is no specific order required for the VA and VBD supplies at power up, however both VA and VBD must be stable for proper operation. The AINP or CHn input signals should not exceed +VA+0.3V per the Absolute Maximum Ratings Table, therefore, AVDD needs to be on prior applying signals to the analog inputs. 

    Thank you and Best Regards,

    Luis