Host Processor Operation
3-4
3.2.2
Output Gain of Two
This configuration allows the DAC output with a gain of two, but is limited to
the effective rails of the operational amplifier. When the DAC7731 is
configured to operate in bipolar mode, the DAC output must be within the
range of 12 V
P - P
or less. Anywhere above the range of 12 V
P - P
clips the output
of the op amp. Likewise, when operating the DAC in unipolar mode, the DAC
output must not exceed 6 V
P - P
.
Table 3 - 3 shows the proper jumper settings of the EVM for the 2
×
gain output
of the DAC.
Table 3 - 3. Gain of Two Output Jumper Settings
Reference
Setting
Function
W5
1 - 2 (Bipolar)
2 - 3 (Unipolar)
Negative rail of the op amp tied to - 15 V for bipolar operation or AGND for
unipolar operation.
W13
3 - 4
Amplified output of DAC is channeled to the output terminal J4 - 6
W15
Close
Configures op amp for a 2
×
gain output
3.2.3
Capacitive Load Drive
Another output configuration option is to drive a wide range of capacitive load
requirement. However, all op-amps under certain conditions can become
unstable depending on the op-amp configuration, gain, and load value. These
are just a few factors that can affect op-amps stability performance and should
be considered when implementing.
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
even more capacitance, and adding a load resistor further improves the
capacitive load drive capability.
Table 3 - 4 shows the jumper setting configuration for a capacitive load drive.
Table 3 - 4. Capacitive Load Drive Output Jumper Settings
Reference
Setting
Function
W5
1 - 2 (Bipolar)
2 - 3 (Unipolar)
Negative rail of the op amp tied to - 15 V for bipolar operation or AGND for
unipolar operation.
W13
5 - 6
Capacitive load drive output of DAC is channeled to the output terminals
W15
Open
Disconnect R12 (see Note)
Note:
If there is a need to incrementally adjust the capacitive load output, replace R12 with a capacitor having the desired ca-
pacitance value and close W15.
