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EVM Operation
5.4.1 Bipolar Output Operation
Using the external V
REF
H to offset the DAC output and extend the range of operation to achieve a bipolar
mode of operation is possible by properly configuring the output operational amplifier, U2. This
configuration is described in Table 4.
Table 4. Bipolar Output Operation Jumper Settings
Reference Jumper Function
Setting
1-2 Connects DAC output (V
OUT
1) to the noninverting input of the output operational amplifier, U2.
W9
2-3 Connects DAC output (V
OUT
2) to the noninverting input of the output operational amplifier, U2.
W3 CLOSE Connect V
REF
H to the inverting input of the operational amplifier, U2.
W5 1-2 Supplies power, V
SS
, to the negative rail of operational amplifier, U2, for wider range of operation.
W12 OPEN Disconnect negative input of the operational amplifier from the gain resistor, R12.
5.4.2 Output Gain of Two Operation
The configuration as described on Table 5 yields a voltage output mode of operation that is gained by two.
Table 5. Gain of Two Output Jumper Settings
Reference Jumper Function
Setting
1-2 Connects DAC output (V
OUT
1) to the noninverting input of the output operational amplifier, U2.
W9
2-3 Connects DAC output (V
OUT
2) to the noninverting input of the output operational amplifier, U2.
W3 OPEN Disconnect V
REF
H from the inverting input of the operational amplifier, U2.
W5 1-2 Supplies power, V
SS
, to the negative rail of operational amplifier, U2, for wider range of operation.
W12 CLOSE Connect the negative input of the operational amplifier, U2, to the gain resistor, R12.
5.4.3 Capacitive Load Drive
Another output configuration option is to drive a wide range of capacitive load requirement. However, all
operational amplifiers under certain conditions may become unstable depending on the operational
amplifier configuration, gain, and load value. These are just a few factors that can affect operational
amplifiers stability performance and must be considered when implementing.
In unity gain, the OPA211 operational amplifier, U2, performs well with large capacitive loads. Increasing
the gain enhances the amplifier’s ability to drive even more capacitance, and adding a load resistor even
improves the capacitive load drive capability.
Table 6 shows the jumper setting configuration for a capacitive load drive.
Table 6. Capacitive Load Drive Output Jumper Settings
Reference Jumper Function
Setting
1-2 Connects DAC output (V
OUT
1) to the noninverting input of the output operational amplifier, U2.
W9
2-3 Connects DAC output (V
OUT
2) to the noninverting input of the output operational amplifier, U2.
W3 OPEN Disconnect V
REF
H to the inverting input of the operational amplifier, U2.
W5 1-2 Supplies power, V
SS
, to the negative rail of operational amplifier, U2, for wider range of operation.
W12 CLOSE Connect the negative input of the operational amplifier, U2, to the gain resistor, R12.
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SLAU279A–March 2009–Revised November 2009 DAC9881 Evaluation Module
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