DAC8811 Datasheet, PDF (12/29 Pages) Texas Instruments – 16-Bit, Serial Input Multiplying Digital-to-Analog Converter

DAC8811
SLAS411D – NOVEMBER 2004 – REVISED FEBRUARY 2016
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Feature Description (continued)
Each DAC code determines the 2R leg switch position to either GND or I_OUT. Because the DAC output
impedance as seen looking into the I_OUT terminal changes versus code, the external I/V converter noise gain will
also change. Because of this, the external I/V converter op amp must have a sufficiently low offset voltage such
that the amplifier offset is not modulated by the DAC I_OUT terminal impedance change. External op amps with
large offset voltages can produce INL errors in the transfer function of the DAC8811 due to offset modulation
versus DAC code. For best linearity performance of the DAC8811, an operational amplifier (OPA277) is
recommended (Figure 19). This circuit allows V_REF swinging from -10 V to +10 V.
Figure 19. Voltage Output Configuration
8.3.1 Stability Circuit
For a current-to-voltage design (see Figure 20), the DAC8811 current output (I_OUT) and the connection with the
inverting node of the op amp should be as short as possible and according to correct PCB layout design. For
each code change, there is a step function. If the GBP of the op amp is limited and parasitic capacitance is
excessive at the inverting node then gain peaking is possible. Therefore, for circuit stability, a compensation
capacitor C1 (4 pF to 20 pF typ) can be added to the design, as shown in Figure 20.
Figure 20. Gain Peaking Prevention Circuit With Compensation Capacitor
8.3.2 Positive Voltage Output Circuit
As Figure 21 illustrates, in order to generate a positive voltage output, a negative reference is input to the
DAC8811. This design is suggested instead of using an inverting amp to invert the output due to tolerance errors
of the resistor. For a negative reference, V_OUT and GND of the reference are level-shifted to a virtual ground and
a –2.5 V input to the DAC8811 with an op amp.
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