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DAC7822: Resistors for standard voltage scaling

Rob Gaddi
Prodigy 130 points
Part Number: DAC7822


There's what seems to be a discrepancy in the datasheet (SBAS374A) regarding how you get the standard unipolar behavior (Vout = -Vref * CODE / 4096) from the DAC7822.  Figure 38 shows R1 and Rfb connected in parallel for this configuration, i.e. the total feedback resistance in the loop should be R.  But Figures 39 and 40 show only Rfb connected, i.e. a feedback resistance of 2R.

Which one is right?

  • 0
    TI__Guru 55253 points

    Hi Rob,

    Figure 38 is correct for generating Vout = -Vref * CODE / 4096.  The R1 and RFB would need to be in parallel to match the resistor ladder impedance.  I will forward this comment to our system's team.  Figure 40 is incorrect.  Figure 39 is more about the compensation cap placement to attenuate gain peaking, so it is independent.