DAC8811ICDGKT Datasheet, PDF (10/21 Pages) Texas Instruments – 16-Bit, Serial Input Multiplying Digital-to-Analog Converter

DAC8811
SLAS411B – NOVEMBER 2004 – REVISED FEBRUARY 2007
APPLICATION INFORMATION (continued)
+2.5V Reference ^VDD
V_OUT V_IN
GND
V_DD ^{RFB C1}
−
V_REF
+
−2.5V
OPA277
DAC8811
GND
I_OUT
OPA277
−
+
V_OUT
0 3 V_OUT 3 +2.5V
Figure 21. Positive Voltage Output Circuit
www.ti.com
Bipolar Output Circuit
The DAC8811, as a 2-quadrant multiplying DAC, can be used to generate a unipolar output. The polarity of the
full-scale output I_OUT is the inverse of the input reference voltage at V_REF.
Some applications require full 4-quadrant multiplying capabilities or bipolar output swing. As shown in Figure 22,
external op amp U4 is added as a summing amp and has a gain of 2X that widens the output span to 5 V. A
4-quadrant multiplying circuit is implemented by using a 2.5-V offset of the reference voltage to bias U4.
According to the circuit transfer equation given in Equation 2, input data (D) from code 0 to full scale produces
output voltages of V_OUT = -2.5 V to V_OUT = +2.5 V.
ǒ Ǔ V_OUT +
D
32, 768
*1
V _REF
(2)
External resistance mismatching is the significant error in Figure 22.
10 kW
10 kW
+2.5V
(+10V)
V_DD
V_DD
R_FB
V_{REF DAC8811}
GND
I_OUT
5 kW
C1
−
+ _U2
OPA277
C2
−
+
U4
OPA277
V_OUT
−2.5V 3 V_OUT 3 +2.5V
(−10V 3 V_OUT 3 +10V)
Figure 22. Bipolar Output Circuit
Programmable Current Source Circuit
A DAC8811 can be integrated into the circuit in Figure 23 to implement an improved Howland current pump for
precise voltage to current conversions. Bidirectional current flow and high voltage compliance are two features of
the circuit. With a matched resistor network, the load current of the circuit is shown by Equation 3:
I_L
+
(R2)R3)
R3
ń
R1
V _REF
D
(3)
10
Submit Documentation Feedback