Texas Instruments DAC8554EVM, Руководство пользователя, Страница: 16 / 24

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EVM Operation
3.4.1 Unity Gain Output
The buffered output configuration can be used to prevent loading of the DAC8554, 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
Disconnect V
REF
H from the inverting input of the op
JMP5 Open Open
amp.
Supplies V
SS
to the negative rail of the op amp or
JMP10 2-3 1-2
ties it to AGND.
Disconnect negative input of op amp from the gain
JMP6 Open Open
resistor, R9.
3.4.2 Output 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 V
REF
H
as an offset. Table 5 shows the proper jumper settings of the EVM for the DAC8554 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
Close Close connected to V
REF
H for use as its offset voltage
with a gain of 2. JMP6 must be open.
JMP5
V
REF
H is disconnected from the inverting input of
Open Open
the output op amp U2. JMP6 must be closed.
Supplies power, V
SS
, to the negative rail of op amp
JMP10 2-3 1-2 U2 for bipolar mode, or ties it to AGND for unipolar
mode.
Configures op amp U2 for a gain of 2 output
Close Close
without a voltage offset. JMP5 must be open.
JMP6
Inverting input of op amp U2 is disconnected from
Open Open
the gain resistor, R9. JMP5 must be closed.
16 DAC8554EVM User's Guide SBAU121 – January 2006