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3.4.1
Unity Gain Output
3.4.2
Output Gain of 2
EVM Operation
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 0
Ω
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 V
REF
H from the inverting input of the op amp.
JMP10
2-3
1-2
Supplies V
SS
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.
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 V
REF
H
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
Function
Inverting input of the output op amp U2 is connected to V
REF
H for use as its offset
Close
Close
voltage with a gain of 2. JMP6 must be open.
JMP5
V
REF
H is disconnected from the inverting input of the output op amp U2. JMP6 must be
Open
Open
closed.
Supplies power, V
SS
, to the negative rail of op amp U2 for bipolar mode, or ties it to
JMP10
2-3
1-2
AGND for unipolar mode.
Configures op amp U2 for a gain of 2 output without a voltage offset. JMP5 must be
Close
Close
open.
JMP6
Inverting input of op amp U2 is disconnected from the gain resistor, R9. JMP5 must be
Open
Open
closed.
DAC8555EVM User's Guide
18
SLAU204 – December 2006
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