DAC8811ICDGKT Datasheet, PDF (8/21 Pages) Texas Instruments – 16-Bit, Serial Input Multiplying Digital-to-Analog Converter

DAC8811
SLAS411B – NOVEMBER 2004 – REVISED FEBRUARY 2007
THEORY OF OPERATION
www.ti.com
The DAC8811 is a single channel current output, 16-bit digital-to-analog converter (DAC). The architecture,
illustrated in Figure 17, is an R-2R ladder configuration with the three MSBs segmented. Each 2R leg of the
ladder is either switched to GND or the I_OUT terminal. The I_OUT terminal of the DAC is held at a virtual GND
potential by the use of an external I/V converter op amp. The R-2R ladder is connected to an external reference
input V_REF that determines the DAC full-scale current. The R-2R ladder presents a code independent load
impedance to the external reference of 5 kΩ ±25%. The external reference voltage can vary in a range of -15 V
to 15 V, thus providing bipolar I_OUT current operation. By using an external I/V converter and the DAC8811 R_FB
resistor, output voltage ranges of -V_REF to V_REF can be generated.
V_REF
R
R
R
2R 2R 2R 2R 2R 2R 2R
2R
2R
2R
2R
2R
R_FB
I_OUT
GND
Figure 17. Equivalent R-2R DAC Circuit
When using an external I/V converter and the DAC8811 R_FB resistor, the DAC output voltage is given by
Equation 1:
V_OUT + *V_REF
CODE
65536
(1)
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 op amp (OPA277) is recommended
(Figure 18). This circuit allows V_REF swinging from -10 V to +10 V.
V_DD
U1
V_DD
R_FB
V_REF
DAC8811
I_OUT
GND
U2 ^{15 V}
_ V+
OPA277
V_O
+
V−
−15 V
Figure 18. Voltage Output Configuration
8
Submit Documentation Feedback