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Original question:

DAC8568: DAC80508EVM software installation problems on Win'10 64 bit.

DAC8568: DAC80508 setting DIV=1 & GAIN=1 are not recommended, why?

Andrzej Szupiluk
Prodigy 230 points
Part Number: DAC8568
Other Parts Discussed in Thread: DAC80508, INA1620

Hi, Paul

Another question.

See Table 1 in data sheet of DAC80508.

Setting DIV=1 and GAIN=1 are not recommended.

Why?

I very need this setting. What is the problem with these?

Best regards

Andrzej

  • 0
    TI__Guru 53693 points

    Hi Andrzej,

    The root of the is that the resistor ladder internal to the DAC performance better with additional headroom from the internal reference voltage and the supply.  The settings of DIV=1 and GAIN=1 will give the system unity gain (output is 0V to VREF).  The same range can be achieved by setting DIV=2 and GAIN=2, but you will see better performance with lower VDD voltages. 

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 230 points

    Hi, Paul

    Thanks.

    It is OK, but DIV switches all channels simultaneously  and GAIN switches only ONE single channel.

    Example:

    I need output of ch.0 in the range 0..5V, and output from ch1 in the range 0..2.5V from single DAC80508 chip.

    I can use OPA and resistors to make it, of course, but precision OPA's and resistors are not cheap!

    What is correct solution to this problem?

    Best regards 

    Andrzej

  • 0 in reply to Andrzej Szupiluk
    TI__Guru 53693 points

    Hi Andrzej,

    The reference divider is really only required for the lower VDD supply configurations.  If you are using the 5V range then I assume you have a 5.5V supply for the device.  If that is correct, you can skip the divider and then just set the gain values accordingly.  So the DAC80508 should be good.

    Thanks,

    Paul

    P.S. While on the subject of precision op amps and resistors: TI recently released the INA1620, which is two precision amps with 4 pairs of precision, laser-trimmed resistors integrated into the same package.  Pretty cool!

  • 0 in reply to Paul_Frost
    Prodigy 230 points

    Hi, Paul 

    Thanks.

    Initially I've set Vdd to 5.2V.

    Is it enough to set DIV to 1 and GAIN to 1 or 2 for different channels inside single DAC80508 chip?

    One from settings above is "not recommended" but if Vdd is greater than 5V it "is recommended" again.

    I'm very glad from this situation.

    Regards

    Andrzej

    PS. I'll see INA1620 chip. Good idea, if the price will be acceptable.

  • 0 in reply to Andrzej Szupiluk
    TI__Guru 53693 points

    Hi Andrzej,

    You can use DIV=1 and GAIN = 1 or 2 with that supply value.  You should not see a drop in performance.

    Thanks!

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 230 points

    Hi Paul

    Thanks. I think, the case is over.

    Best regards

    Andrzej

    PS. Due to noise reasons and external need/usage, I finally won't use internal DAC80508 voltage reference.