Datasheet
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THEORY OF OPERATION
V
OUT
+ −V
REF
CODE
16384
(1)
V
REF
GND
I
OUT
2R
2R 2R 2R 2R 2R 2R 2R 2R 2R 2R 2R R
FB
R R
R
_
+
OPA277
V+
V−
15 V
−15 V
V
O
V
DD
R
FB
I
OUT
GND
DAC8801
U2
U1
V
DD
V
REF
DAC8801
SLAS403B – NOVEMBER 2004 – REVISED FEBRUARY 2007
The DAC8801 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 k Ω ± 25%. The external reference voltage can vary in a range of -10 V
to 10 V, thus providing bipolar I
OUT
current operation. By using an external I/V converter and the DAC8801 R
FB
resistor, output voltage ranges of -V
REF
to V
REF
can be generated.
When using an external I/V converter and the DAC8801 R
FB
resistor, the DAC output voltage is given by
Equation 1 :
Figure 17. Equivalent R-2R DAC Circuit
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 DAC8801 due to offset modulation
versus DAC code. For best linearity performance of the DAC8801, an op amp (OPA277) as shown in Figure 18
is recommended. This circuit allows V
REF
to swing from -10V to +10V.
Figure 18. Voltage Output Configuration
8
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