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Forum Post: RE: DAC7811 adjusts voltage option

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[quote user="Fawad Munawar"]

I am using 8 of AFE5809 chips to get more channel options .My main concern  is In the  TGC section producing VCNTL signals.(VCNTL_IN_P/VCNTL_IN_N)

 This signal is an analog signal that controls the attenuator in the RX AFEs. In the most typical case it provides a ramp voltage to the RX AFE. what voltage range VCNTL signal should be used ?

[/quote]

I am not familiar with the AFE5809, but from looking at the datasheet and the schematics that your provided, I do think that the DAC output range should be from 0V to +1.5V. I think that you can use a single ended input to VCNTLP by grounding VCNTLM. As opposed to a differential input.

For more details on this specification please refer to the Medical Forum, they take care of this AFE5809 part.

[quote user="Fawad Munawar"]Can I use 0V to +1.5V or it should be always be 10v  and -10 v  that is mentioned in datasheet .[/quote]

I assume you are referring to figure 26 in the DAC7811 datasheet.

The DAC can actually use a ±15V reference voltage and anywhere in between, so you can supply a voltage anywhere from -15V to +15V. In this design the limiting factor is the OPA277 amplifier rails.

The DAC7811 is perfectly capable of supplying an output voltage from 0V to +1.5V, you will need a -1.5V reference

[quote user="Fawad Munawar"]See attached design for your review.[/quote]

I am unsure as to what the purpose of U114 is. Typically we add a trans-impedance stage to convert the current output of the DAC to voltage. As you can see in figure 26.


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