DAC7811 Datasheet, PDF (12/18 Pages) Texas Instruments – 12-Bit, Serial Input, Multiplying Digital-to-Analog Converter

DAC7811
SBAS337 – APRIL 2005
Table 3. Serial Input Register Data Format, Data Loaded MSB First
C3
C2
C1
0
0
0
0
0
0
0
0
1
0
0
1
0
1
0
0
1
0
0
1
1
0
1
1
1
0
0
1
0
0
1
0
1
1
0
1
1
1
0
1
1
0
1
1
1
1
1
1
C0
FUNCTION IMPLEMENTED
0
No operation (power-on default)
1
Load and update
0
Initiate readback
1
Reserved
0
Reserved
1
Reserved
0
Reserved
1
Reserved
0
Reserved
1
Daisy-chain disable
0
Clock data to shift register on rising edge
1
Clear DAC output to 0
0
Clear DAC output to midscale
1
Reserved
0
Reserved
1
Reserved
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APPLICATION INFORMATION
Stability Circuit
For a current-to-voltage design (see Figure 29), the DAC7811 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 printed circuit board (PCB)
layout design. For each code change, there is a step function. If the gain bandwidth product (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 29.
V_DD
U1
V_DD
R_FB
C₁
V_REF
V_REF
GND
I_OUT1
I_OUT2
V_OUT
U2
Figure 29. Gain Peaking Prevention Circuit with Compensation Capacitor
Positive Voltage Output Circuit
As Figure 30 illustrates, in order to generate a positive voltage output, a negative reference is input to the
DAC7811. This design is suggested instead of using an inverting amp to invert the output as a result of resistor
tolerance errors. 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 DAC7811 with an op amp.
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