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THS4509: Full-scale range input of ADS5294

BongJo Joung
Prodigy 110 points
Part Number: THS4509
Other Parts Discussed in Thread: ADS5294

Hello,

I want to convert a 0V to 2V single-ended signal to a differential signal using the THS4509 and then connect it to an ADS5294 ADC.

Is it possible to achieve a full-scale range in the ADC by configuring it as shown in the diagram below?

If possible, could you please confirm how it should be configured to achieve this?

Thank you.

  • 0
    TI__Genius 11665 points

    Hi BongJo,

    There are a few configurations that would work for this device. Section 9.2.1.2.3 highlights three potential solutions each with their own difficulties. The problem this FDA+ADC combination will cause is that the recommended Vcm for the ADC will not work in a typical 0V to 5V supply configuration as the lower output limit is 1V for the FDA. This is what is causing the green signal to slam to the lowest output, this would result in a very distorted signal. The section highlighted above does mention one solution that could be implemented without major change however this would force you to skew the supplies. Are the single supply 5V a fixed requirement? If so, you could implement something like the circuit I attached. This implements the circuit in Figure 83, but then AC couples the outputs and biases them to the recommended Vcm of the ADC.

    Best Regards,

    Ignacio

    THS4509_ADC.TSC

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 110 points

    Hi, Ignacio

    Thank you for your help.

    I tested as per your advice. However, the ADC input value is always around 8192. It seems that DC is being cut, possibly due to the 500nF capacitor.

    And, the single supply 5V of THS4509 can be adjusted. Additionally, dual supply is also supported.

    When input values in the range of 0V to 2V are present, could you please reconfirm how the circuit should be modified to achieve ADC input reception at full scale (2Vpp)?

    Best Regards,

    BongJo

  • 0 in reply to BongJo Joung
    TI__Genius 11665 points

    Hi BongJo,

    If your design allows you to skew the supplies to any value, you could simply skew the supplies to +3.5V and -1.5V and connect Vocm to 0.95V. This would simplify the design significantly as you will not need to ac couple the outputs and bias the output like in the previous design. The tina sim simulates this circuit with skewed supplies and a 2Vpp input signal. 

    Best regards,

    Ignacio

    THS4509_ADC_skewed.TSC