THS4130: Current consumption at Vocm

Austin Do

Part Number: THS4130
Other Parts Discussed in Thread: ADS9219EVM, OPA320

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

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 325670 points

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

0 Alec Saebeler over 1 year ago

TI__Mastermind 24524 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 Austin Do over 1 year ago in reply to Clemens Ladisch

TI__Expert 4025 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 Austin Do over 1 year ago in reply to Alec Saebeler

TI__Expert 4025 points

Hi Alec,

Thanks for reply. This reference helps me a lot

Best Regards,

Austin

+1 Clemens Ladisch over 1 year ago in reply to Austin Do

Guru 325670 points

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

You have to compute the current that flows into or out of the V_OCM pin. For example, assuming that V_CC+ and V_CC− are connected to ±10 V, and that the V_OCM 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 Alec Saebeler over 1 year ago in reply to Austin Do

TI__Mastermind 24524 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

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THS4130: Current consumption at Vocm