ADC3641: VREF pin question

Artem B

Part Number: ADC3641

Tool/software:

Hi everyone.

I've seen in the datasheet that both internal and external VREF may be used. In case of using an internal VREF, the capacitors shall be installed on VREF pin.

Does it mean that there's VREF voltage (1.6V) on VREF pin that may be used externally?

I have differential ADC driver with input from ADC VREF. It uses VREF to clamp the output voltage.

Thanks,

Artem B.

9 months ago

0 Rob Reeder 9 months ago

TI__Mastermind 37830 points

Hi Artem,

Yes, you can use the VREF pin as a external reference for the ADC driver amplifier.

However, please do the following to ensure the 1.6V VREF is not loaded down.

Put the capacitors near the VREF pin of the ADC as the datasheet specifies.

Use an 1xamplifier/follower on the VREF pin and connect it to the input VOCM pin of the ADC driver.

Put a 0.1uF cap at the VOCM pin of the ADC driver.

Here is a picture which will help describe.

Regards,

Rob

0 Artem B 9 months ago in reply to Rob Reeder

Prodigy 40 points

Hi Rob, thanks for your answer.

There are 2 pins in this ADC: VCM and VREF.

I know that VCM is used as common mode voltage output.

But I didn't find any information about VREF pin usage as an reference voltage output. In datasheet, it is mentioned as input only.

Thanks,

Artem B.

0 Rob Reeder 9 months ago in reply to Artem B

TI__Mastermind 37830 points

Hi Artern,

If you probe the VREF pin, it is sitting at 1.6V.

What FDA do you plan to use as the ADC driver?

Regards,

Rob

0 Artem B 9 months ago in reply to Rob Reeder

Prodigy 40 points

Hi Rob,

What do you mean by FDA?

I'm planning to use Analog Devices ADA4945 as a driver.

Do you have information about ADC's VREF pin output impedance?

Thanks,

Artem B.

0 Rob Reeder 8 months ago in reply to Artem B

TI__Mastermind 37830 points

Arterm,

FDA = fully differential amplifier

VREF impedance is listed on page 8 of the datasheet.

Thanks,

Rob

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ADC3641: VREF pin question