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DAC8760: DAC8760

Luca Ferrari45
Prodigy 30 points
Part Number: DAC8760

Hi everyone.

I have one problem with DAC8760 using it in 4-20mA (single) output. NOT USING BOOST output! And connecting like your DAC8760EVM board.

I have setted Rset external, 15Kohm (+ 196Kohm) to obtain more than 20mA corrent output. Before was 19.997mA...

I don't know how to enlarge the lower limit... It seems impossible to go under 4mA!!!

Can you suggest me about one configuration to reduce Iout minimum under 4mA. Thank you very for all you'll be able to reply. It's an urgent question.

So waiting for a fast reply.

Nice day. 

  • 0
    TI__Expert 5820 points

    Hi Luca,

    If I am understanding your question correctly, you are asking how to get the device to output less than 4mA?

    An output under 4mA can be accomplished by setting the IOUT range bits to either the 0-20mA range or 0-24mA range. Then the zero scale code will be 0mA. See table 12 in the datasheet for the range settings.

    Thanks,
    Garrett

  • 0 in reply to Garrett Satterfield
    Prodigy 30 points
    Hi Garrett. Thank you very much for your fast reply.
    That you have proposed is correct but that (alternative) settings bring us to obtain lower resolution on the output current scale.
    Why the device is not prevented to have a current value (a little) lower than 4mA for having the complete range without the flat zone output (at 4mA about) with lowest values of the DAC?
    Must I use the boost pin to have this "extended" range?
    Please, tell me what are you thinking about this.
    Best regards.
  • 0 in reply to Luca Ferrari45
    Prodigy 30 points
    What do you think about HART signal? I don't need it. To disable is enough putting the relative bit in the control register to zero, connecting a resistor (15Kohm) to ground at pin ISET-R (doubts about this... The resistor is hot at 20mA...) And connecting a capacitor (22nF) to ground?
    Please, tell me.
  • 0 in reply to Luca Ferrari45
    TI__Expert 5820 points

    Hi Luca,

    Using the boost transistor really just offers the advantage of lower on-chip power dissipation. So using this option will not change the range. We recommend using the internal resistor in most cases, as using the external ISET-R contributes some gain error. I believe the only way you will be able to get a bit below 4mA is to use one of the other ranges and not use some of the codes.

    It is fine to connect a 15kohm resistor from ISET-R to ground as specified in the datasheet. You do not need a capacitor connected to ISET-R unless you are coupling the HART into as stated in 9.1.2.2 of the datasheet. If you are not using HART we recommend connecting a 22nF capacitor from the HART pin to ground.

    Thanks,
    Garrett