Datasheet
www.ti.com
Control Bits C3 to C0
APPLICATION INFORMATION
Stability Circuit
I 1
OUT
V
OUT
R
FB
C
1
GND
V
DD
V
DD
U1
U2
V
REF
V
REF
I 2
OUT
DAC7811
SBAS337C – APRIL 2005 – REVISED JULY 2007
Control Bits C3 to C0 allow control of various functions of the DAC; see Table 2 . Default settings of the DAC on
powering up are as follows: Data clocked into shift register on falling clock edges; daisy-chain mode is enabled.
The device powers on with zero-scale loaded into the DAC register and I
OUT
lines. The DAC control bits allow
the user to adjust certain features as part of an initialization sequence; for example, daisy-chaining may be
disabled if not in use, active clock edge may be changed to rising edge, and DAC output may be cleared to
either zero or midscale. The user may also initiate a readback of the DAC register contents for verification
purposes.
Table 2. Serial Input Register Data Format, Data Loaded MSB First
C3 C2 C1 C0 FUNCTION IMPLEMENTED
0 0 0 0 No operation (power-on default)
0 0 0 1 Load and update
0 0 1 0 Initiate readback
0 0 1 1 Reserved
0 1 0 0 Reserved
0 1 0 1 Reserved
0 1 1 0 Reserved
0 1 1 1 Reserved
1 0 0 0 Reserved
1 0 0 1 Daisy-chain disable
1 0 1 0 Clock data to shift register on rising edge
1 0 1 1 Clear DAC output to zero
1 1 0 0 Clear DAC output to midscale
1 1 0 1 Reserved
1 1 1 0 Reserved
1 1 1 1 Reserved
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 practices. 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 C
1
(1pF to 5pF typ) can be added to the design, as
shown in Figure 29 .
Figure 29. Gain Peaking Prevention Circuit with Compensation Capacitor
13
Submit Documentation Feedback