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EVM Operation
3.4.1Unity Gain Output
The buffered output configuration can be used to prevent loading of the DAC8555, though it may add some slight distortion because of the feedback resistor and capacitor. The feedback circuit can be altered by simply desoldering R8 and C12 and replacing them with components of desired value. If desired, R8 and C12 can be removed altogether by replacing R8 with a 0Ω resistor.
Table 4 shows the jumper setting for the unity gain configuration of the DAC external output buffer in unipolar or bipolar mode.
Table 4. Unity Gain Output Jumper Settings
| Jumper Setting |
| |
Reference | Unipolar | Bipolar | Function |
JMP5 | Open | Open | Disconnect VREFH from the inverting input of the op amp. |
JMP10 | Supplies VSS to the negative rail of the op amp or ties it to AGND. | ||
JMP6 | Open | Open | Disconnect negative input of op amp from the gain resistor, R9. |
3.4.2Output Gain of 2
There are two types of configurations that will yield an output gain of 2, depending on the setup of jumpers JMP5 and JMP6. These configurations allow the user to choose whether the DAC output will use VREFH as an offset. Table 5 shows the proper jumper settings of the EVM for the DAC8555 output gain of 2.
Table 5. Output Gain of 2 Jumper Settings
| Jumper Setting | |
Reference | Unipolar | Bipolar |
| Close | Close |
JMP5 |
|
|
| Open | Open |
JMP10 | ||
| Close | Close |
JMP6 |
|
|
| Open | Open |
Function
Inverting input of the output op amp U2 is connected to VREFH for use as its offset voltage with a gain of 2. JMP6 must be open.
VREFH is disconnected from the inverting input of the output op amp U2. JMP6 must be closed.
Supplies power, VSS, to the negative rail of op amp U2 for bipolar mode, or ties it to AGND for unipolar mode.
Configures op amp U2 for a gain of 2 output without a voltage offset. JMP5 must be open.
Inverting input of op amp U2 is disconnected from the gain resistor, R9. JMP5 must be closed.
18 | DAC8555EVM User's Guide | SLAU204 |
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