Datasheet

Host Processor Interface
3-8
Table 3–3.Unity Gain Output Jumper Settings
Reference
Jumper
Setting
Function
W7 1–2 + Rail of the op-amp supplied by V
CCA
W8 1–2 – Rail of the op-amp tied to analog GND
W10 Open Disconnect V
REF
from negative input of op-amp
W11 Open Disconnect negative input of op-amp from GND
W13 3–4 Buffered output of DAC is channeled to the output terminals
3.2.2.2 Output Gain of Two
If the EVM is operating at 3.3 V and there is a need for the DAC output to
maintain a 5-V peak level, than this configuration can be implemented.
Table 3–4 shows the proper jumper settings for a 2× gain output of the DAC.
Table 3–4.Gain of Two Output Jumper Settings
Reference
Jumper
Setting
Function
W7 2–3 Select 5 V for the positive rail supply of the op-amp if W12 is closed
W8 1–2 Negative rail of the op-amp tied to analog GND
W10 Open Disconnect V
REF
from negative input of op-amp
W11 Close Provides a 2× gain output for the op-amp
W12 Close
Supplies the constant 5 V to the positive rail of the op-amp if W7, pins 2 and 3, are
shorted together
W13 3–4 Buffered output of DAC is channeled to the output terminals
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, U12. Otherwise
the output of the op-amp, U12, will be clipped.
V
CCA
can be used also to supply the positive rail of the op-amp by shorting pins
1 and 2 of W7. With this configuration, the effective output of the op-amp will
be at a maximum of V
CCA
. The reference voltage must also be set to V
CCA
/2.
3.2.2.3 Capacitive Load Driving
Another output configuration option is to drive a wide range of capacitive loads.
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-amp stability performance and should be
considered during implementation.
In unity gain, the OPA350 op-amp, U12, performs very well with very large
capacitive loads. Increasing the gain enhances the amplifier’s ability to drive
even more capacitance, and by adding a load resistor improves the capacitive
load drive capability. Table 3–5 shows the jumper setting configuration for a
capacitive load drive.