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THS4130: Current consumption at Vocm

Austin Do
Expert 3295 points
Part Number: THS4130
Other Parts Discussed in Thread: ADS9219EVM, OPA320, REF3450

Tool/software:

Hello team,

What is the current consumption at Vocm pin? The customer would like to connect voltage reference output with this pin. So, wants to double confirm the exact value.

Best Regards,

Austin

  • 0
    Guru 317090 points

    The voltage reference must be able to override the 2× 30 kΩ voltage divider; the actual current depends on the voltage.

  • 0
    TI__Mastermind 22794 points

    Hello Austin,

    Good question; Clemens provided a good answer in his earlier response.  

    You can look at ADC EVMs from TI, such as ADS9219EVM, to see how FDAs and ADCs are connected, including supporting circuitry such as REF7040.

    On the EVM I mentioned, the OPA320 buffers the VCM output of the ADC to drive the VOCM pin on the FDA.  You have several options when designing for external VOCM.

    Best,

    Alec

  • 0 in reply to Clemens Ladisch
    TI__Expert 3295 points

    Hi Clemens,

    If output swing has 2Vpp with 5V common mode voltage, max current consumption becomes (6V-5V) / 30kohm = 33uA. Is my understanding correct?

    Best Regards,

    Austin

  • 0 in reply to Alec Saebeler
    TI__Expert 3295 points

    Hi Alec, 

    Thanks for reply. This reference helps me a lot

    Best Regards,

    Austin

  • +1 in reply to Austin Do
    Guru 317090 points

    The output voltage does not matter; the VOCM and VOUT pins are isolated from each other.

    You have to compute the current that flows into or out of the VOCM pin. For example, assuming that VCC+ and VCC− are connected to ±10 V, and that the VOCM pin is connected to a REF3450 with a 5 V output, then the current through the upper resistor is (10 V − 5 V) / 30 kΩ = 167 µA, and through the lower, (5 V − (−10 V)) / 30 kΩ = 500 µA. The difference is 333 µA, and must be sourced by the reference. (The REF3450 is capable of that.)

  • +1 in reply to Austin Do
    TI__Mastermind 22794 points

    Hello Austin,

    I am glad we have been able to help.  Let us know if your question is resolved or if you require more support.

    Best,

    Alec