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ADS1299: ADS1299 VCAP1 charging time

Vinaayaka M
Prodigy 40 points
Part Number: ADS1299
Other Parts Discussed in Thread: ADS1298, ADS1294

Hi Team,

The recommended capacitor value for VCAP1 in ADS1299 is 100uF and the internal resistor R1 is 9.8kOhms which takes around ~2.4sec for the Vcap1 to reach 1.1V. 

  1. I wanted to know if the wait time until VCAP1 reaches >1.1V as per the the initial flow is really necessary if we are using the external reference?
  2. What is the consequence if we do not wait until this time under both conditions mentioned below?
    1. While using internal reference
    2. While using external reference
  3. Is the consequence same in ADS1298/6/4 ?

Thank you in advance.

  • 0
    TI__Intellectual 2030 points

    Hello Vinaayaka,

    Our device expert is out of office until late next week, so please expect a delay in our response.

    Regards,

    Payton

  • 0 in reply to Payton Schubel
    TI__Guru 66906 points

    Hello Vinaayaka,

    Thank you for your post. 

    The initialization flowchart suggests waiting for VCAP1 to reach 1.1V before issuing a power-on reset pulse in order to ensure the internal one-time programmable bits are read correctly. The recommendation is not related to the ADC reference voltage, so the same advice should be followed for internal or external reference configurations.

    Yes, ADS1294/6/8 also follow this same power-on reset guidance, although the time-constant is lower as the recommended VCAP1 bypass cap is only 22µF.

    Regards,

    Ryan