• Resolved

ADS7953: Timing sequence

Intellectual 440 points

Replies: 6

Views: 140

Part Number: ADS7953

Hello team,

I use ADS7953 in my design, I find the data sampled are error occasionally when power on, but when I power off and power on again, the data sampled are ok.

1.Is there any timing sequence requirement for the +VA,+BD,REFP and SPI interface when power on? Please recommend their power-on sequences.

2.If the SPI are High before the +VA,+BD and REFP? Does ADS7953 can work normally?

3.Does REFP need to be powered on later than +VA?how long should be delayed?

Thank you.

Kevin

  • Hello,

    The analog supply, VA always needs to be at the same level or higher than the digital supply, VBD.The analog supply should be power on before or at the same time as the reference as well.

    When powering up the device, it could act abnormally if the digital supply ramped up before the analog supply.  The digital input to the ADC should also not be High before the ADC is powered up. It is best to fully power up the device first, and then try to communicate with it.

    Regards

    Cynthia

  • In reply to Cynthia:

    Hello Cynthia,

    Thank you for your support.

    If the analog power supply (VA)and the digital power supply (VBD) are powered on at the same time, they are powered by the same power supply(3.3V),will it affect the the ADC working normally when power on?

    How long does reference should be delayed to the analog supply when power on? 20ms, 100ms ,500ms...Is there any delay time limited?

    Thank you.

    Kevin

     

  • In reply to kevin p:

    No problem,

    In general, both power supplies coming up at the same time is usually fine. But I would suggest to confirm that each rail is ramping up together, especially if VA and VBD are at different voltage levels. If VBD is lower, the rail might ramp up faster than VA, which could be causing the issue.

    There doesn't seem to need a specific delay time between REF and VA. This should not cause an error, as long as each supply is settled before conversions are taken place.

    Regards

    Cynthia

  • In reply to Cynthia:

    Hello Cynthia,

    Thank you for your support.

    In my design, the ref2.5V is powered by 3.3V,the VA connected with VBD on same power supply 3.3V.

    The 2.5 is lower than 3.3V, I test the rise time when power on.The ref2.5V is less than 0.5ms powered before 3.3V when power on.Does it will effect normal work?

    Thank you.

    Kevin

  • In reply to kevin p:

    Kevin,

    This should not affect the device

    As long as VRef is settled before making conversions, you should see correct measurements.

    Regards

    Cynthia

  • In reply to Cynthia:

    Hi Cynthia,

    Thank you for your support.

    Kevin