Texas Instruments DAC8534, User Manual, Page: 22 / 27

The Output Op Amp
3-4
3.4.1 Unity Gain Output
The buffered output configuration can be used to prevent loading the
DAC8534, although it may present some slight distortion because of the
feedback resistor and capacitor. Users can tailor the feedback circuit to closely
match their desired wave shape by simply desoldering R7 and C11, and
replacing them with the desired values. If desired, you can also simply remove
R7 and C11 altogether and just solder a 0-
W
resistor in place of R7.
Table 3 - 3 shows the jumper settings for the unity gain configuration of the
DAC external output buffer in unipolar or bipolar mode.
Table 3 - 3. Unity Gain Output Jumper Settings
Jumper Setting
Reference
Unipolar Bipolar
Function
W3 OPEN OPEN Disconnects V
REF
H from the inverting input of the op amp.
W5 2 - 3 1 - 2 Supplies V
SS
to the negative rail of op amp or ties it to AGND.
W15 OPEN OPEN Disconnects negative input of op amp from AGND.
3.4.2 Output Gain of Two
There are two types of configurations that yield a gain of two output depending
on the setup of jumpers W3 and W15. These configurations allow the user to
choose whether the DAC output has V
REF
H as an offset, or not.
Table 3 - 4 shows the proper jumper settings of the EVM for the 2
×
gain output
of the DAC.
Table 3 - 4. Gain of Two Output Jumper Settings
Jumper Setting
Reference
Unipolar Bipolar
Function
Close Close
Inverting input of the output op amp, U2, is connected to V
REF
H for use
as its offset voltage with a gain of 2. W15 jumper must be open.
W3
Open Open
V
REF
H is disconnected from the inverting input of the output op amp, U2.
W15 jumper must be close.
W5 2 - 3 1 - 2
Supplies power, V
SS
, to the negative rail of op amp, U2, for bipolar mode,
or ties it to AGND for unipolar mode.
Close Close
Configures op amp, U2, for a gain of 2 output without a voltage offset. W3
jumper must be open.
W15
Open Open
Inverting input of the op amp, U2, is disconnected from AGND. W3
jumper must be close.
3.4.3 Capacitive Load Drive
Another output configuration option may be a requirement to drive a wide
range of capacitive loads. However, all op amps under certain conditions may
become unstable depending on the op amp configuration, gain, and load
value. These are just few factors that can affect op amp stability performance,
and should be considered when implementing designs for capacitive loads.
In unity gain, the OPA627 op amp, U2, performs very well with very large
capacitive loads. Increasing the gain enhances the amplifier’s ability to drive