Host Processor Operation
3-3
EVM Operation
Table 3 - 2. Unity Gain Output Jumper Settings
Reference
Jumper Position
Function
W3
2 - 3
Negative rail of the op amp tied to analog GND
W4
Don’t care
Positive rail of the op amp can be supplied by 15 V or V
CC
W5
3 - 4
Buffered output of DAC is channeled to the output terminals
W6
Open
Disconnect V
REF(H)
from negative input of op amp
W7
Open
Disconnect negative input of op amp from GND
3.2.2
Output Gain of Two
This configuration allows the output of the DAC to have a gain of two which is
particularly useful when the EVM is operating at 3.3 V and there is a need for
the DAC output to maintain a 5 V peak level. The output gain of two
configuration that can be implemented on this EVM should not exceed the
effective range of 2
×
V
REF(H)
.
The reference voltage must be set such that the output voltage range of the
DAC does not exceed the positive rail supply of the op amp, U2, as well.
Otherwise the output of the op amp, U2, is clipped.
V
CC
can be used also to supply the positive rail of the op amp by shorting pins
1 and 2 of W4. With this configuration, the effective output of the op amp is
at a maximum of V
CC
. The reference voltage must also be set to V
CC
/2.
Table 3 - 3 shows the proper jumper settings for the 2
×
gain output of the DAC.
Table 3 - 3. Gain of Two Output Jumper Settings
Reference
Jumper Position
Function
W3
2 - 3
Negative rail of the op amp tied to analog GND
W4
1 - 2
Positive rail supply of the op amp tied to 15 V
W5
3 - 4
Amplifier output of DAC is channeled to the output terminals
W6
Open
Disconnect V
REF(H)
from negative input of op amp
W7
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
requirements. However, all op-amps under certain conditions may 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 that 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 would even improve the
capacitive load drive capability.
Table 3 - 4 shows the jumper setting configuration for a capacitive load drive.