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ADS7950: ADS7950SBRGET

Kavin Ravi
Prodigy 130 points

Part Number: ADS7950
Other Parts Discussed in Thread: ADS7953EVM-PDK

Tool/software:

Hi,


We’re using the 4-channel ADC ADS7950SBRGET in one of our products. Could you please review the attached schematic and share your feedback?

Thank you.

  • 0
    Prodigy 130 points

    Also, could you please let me know if I can replace the REF5025ID voltage reference IC with a 2.5 V output from a PMIC’s buck converter or LDO?

    Thank you for your support.

  • 0 in reply to Kavin Ravi
    TI__Mastermind 20960 points

    Hi Kavin,

    The ADS7950 schematic looks good. Can you share what the inputs to each channel are? 

    As to replacing the reference with a switching converter, I recommend against it. An LDO could be an okay replacement, as long as the output noise is sufficient for your accuracy target. Keep in mind reference noise directly affects gain error of the ADC.

    Regards,
    Joel

  • 0
    Prodigy 130 points

    Hi Joel,

    Thank you for reviewing the schematic.

    The ADC will be used for two main applications:

    1. Temperature Monitoring: Reading thermistors located on different boards within the system. The thermistors are multiplexed, and the MUX output is routed to the ADC input channel (as shown in the image) for sequential temperature measurements.

    ...

    1. Analog Signal Acquisition: Measuring an analog signal from a separate scientific or experimental subsystem. This signal will be connected to one of the ADC channels for periodic data sampling and monitoring.

    We plan to retain the REF5025ID precision voltage reference IC in the design.

    Thank you.

  • 0 in reply to Kavin Ravi
    TI__Mastermind 20960 points

    Hi Kavin,

    Thanks for sharing. I believe this circuit should perform well. I would recommend running the sampling rate slower, to allow for more acquisition time. This will help the settling performance of the ADC.

    When the mux channel is switched, the ADC can see a large step signal in the input. If the internal sampling capacitor does not have enough time to charge fully to the input voltage, this will result in a settling error.

    Regards,
    Joel

  • 0 in reply to Joel Meraz
    Prodigy 130 points

    Hi Joel,

    Thank you for the recommendation. We will reduce the sampling rate. could you please suggest a suitable window of range?

    Also, regarding PCB routing, should the analog and digital sections be separated? I referred to the ADS7953EVM-PDK Evaluation Module, and it appears that the analog and digital sections are not separated. Would it be acceptable to follow the same approach and use a common solid ground plane (for both analog and digital grounds) across all layers?

    Best regards,

    Kavin

  • 0 in reply to Kavin Ravi
    TI__Mastermind 20960 points

    Hi Kavin,

    As temperature monitoring is usually a fairly slow application, I could see this.

    In general yes, having a shared ground between the analog and digital provides negligible performance impact versus separate ground plane. The main concern is digital noise corrupting analog conversion voltages. For this device resolution and architecture, it is not a concern, and we recommend having a shared ground between the analog and digital if their ground reference can be at the same potential.

    Regards,
    Joel