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Multiple floating DAC outputs (e.g. AMC7832)

Tom Waschura
Prodigy 220 points
Other Parts Discussed in Thread: AMC7832

I have an application where multiple times I need to come up with 10 dac channels who's outputs are 0 to -2.5V below a programmable voltage rail.  The programmable voltage rail goes from -2V to +3V.  I have clean +/- 10.5V supplies available as well.

I can do this with many op-amps, but there must be a cleaner way using clever DACs.

I'm looking at the AMC7832 part (I could use the ADC as well).  The thought would be to power the part between my programmable voltage rail and +5V above that (which I'd get from a linear regulator from the +10.5V rail--it only needs a small amount of current).  I can easily level-shift the three-wire interface.  However, I don't believe I have enough supply to cover the range given that it wants to put out -10V to 0V (relative to my supply) in its inverted output mode.  Perhaps there's some way to reduce this?

Any other thoughts on ways to create MANY negative DAC outputs relative to floating supply level?

Thanks all,   Tom.

  • 0
    TI__Genius 11750 points

    Howdy Tom,


    I apologize for the delay, I may have overlooked this question while on business travel.

    Aside from 12-bit resolution, are there any other metrics to consider for your application, such as DC performance (offset/gain error/ INL).  It seems from your application you want multiple DACs to generate an output span of -2V to 3V.

    The AMC7832 device is capable of 3 fixed ranges:  0 to 5V, 0 to 10V, and -10 to 0V. Although the ranges are fixed the offset can be controlled via the Vrange input pin. The offset is generated from Vrange*4.

    You can bias 0.5V on the Vrange pin to apply a -2V offset, but keep in mind that you can either operate in a 10V or 5V range. As a result the DAC output can be programmed to the below:

    -2 to 3V (5V Range, DAC-5VRANGE bit set to 1) or
    -2 to 8V (10V Range, DAC-5VRANGE bit set to 0)

    All DACs are capable of driving up to +-15mA.

    Additionally, please note that according to the datasheet, the DAC clamp will set to (AVSS +2). 

    Best Regards,

    Matt