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4.4 Analog Output
The analog output of this Eval board is available in
two places. For a DC coupled output, pin 1 of J5
provides V
OUT
and pin 2 provides AGND. An AC
coupled output is provided by the SMA connector
(J4). See
Figure 5
below for details.
If using a spectrum analyzer to look at the output
of the DAC, the AC coupled output (J4) is
recommended.
For very low frequency (i.e. less than 1kHz), use
J5 to see the output signal DC coupled. For an
AC coupled output at low frequencies, simply
replace the AC coupling capacitor at C9 with a
larger capacitor. Use the J4 SMA to look at the
AC coupled output.
Figure 5: Analog Output
4.5 Power Supply Connections
In Computer mode, the board can be powered by
either an external supply or the local WaveVision4
board supply. In Stand-alone mode, the
Evaluation Board must be powered by an external
supply.
If you wish to use the local supply from the
WaveVision4 Board
, place a jumper across pins 1
and 2 of JP9. This connection will 5V to
V
A
on the DAC board. To set V
REF
=V
A
, simply
short pins 2 & 3 of JP7. For WaveVision to
recognize the board, the 3P3V supply must be
enabled as well. Do this by placing a jumper
across pins 1 and 2 of JP10. The board comes
configured to use the local supply. The default
jumper settings are shown in
Figure 1.
If you wish to supply V
A
externally
, connect a DC
voltage supply to connector J2. Connect GND to
the center terminal and V
A
to the bottom terminal.
Place a jumper across pins 2 and 3 of JP9 to
select V
A
_REMOTE. This voltage (V
A
) can be set
anywhere from +2.7V to +5.5V. The source of
V
REF
is controlled by the JP7 jumper. To set
V
REF
=V
A
, short pins 2 & 3. To use an external
V
REF
from the top terminal of J2, short pins 1 & 2.
Refer to
Figure 6
for a diagram of the power
supply connections.
Figure 6: Power Supply Connections
Typical supply currents when applying an external
supply to V
A
and V
REF
are as follows:
•
For V
A
= +3.3V, I = 7mA
•
For V
A
= +5.0V, I = 12mA
Note: These values are specified for a
continuously operating DAC in High Speed Mode,
driving a full-scale sinewave output. The majority
of this current is for powering devices external to
the DAC121C085 such as the pull-up resistors
and the LED.
AC Coupled
V
OUT
V
OUT
AGND
V
REF
V
A
Remote
