Reference Voltage
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6
Reference Voltage
The DAC8728EVM is configured with two different onboard precision references. The evaluation module
has both a +2.5V and +5V reference using the REF5025 and the REF02, respectively. By using the screw
terminal J2, the user can also apply external reference voltages to the board. Any external voltage applied
to J2 must be within the +1.0 to +5.5V reference voltage range specification for the DAC8728. The
DAC8728 has two different references, REF_A for V
OUT
0–V
OUT
3 and REF_B for V
OUT
4–V
OUT
7, respectively.
Using jumpers JP4 to JP7, both REF_A and REF_B can be individually configured to 2.5V, +5V, or
the external reference input voltage. Jumpers JP6 (REF-A) and JP7 (REF-B) are used to select between
using an onboard reference or an external reference. If an onboard reference is selected, jumpers JP4
(REF-A) and JP5 (REF-B) are used to select between the 2.5V or the 5.0V reference. The reference
circuits can be seen in the schematic at the end of this document.
7
EVM Operation
CAUTION
Before power is applied to J4 on the EVM, be sure that the jumpers on the
board are configured according to the factory default settings described below.
This section provides information on the analog input and digital control of the DAC8728EVM, as well as
the default settings.
7.1
Analog Output
The DAC8728 has eight analog outputs that are available at the J5 header or the JP1 and JP2 jumper
headers. Each of these outputs is referenced to the board ground.
Jumpers JP1 and JP2 allow the user to route the DAC outputs to the input of a voltage-follower amplifier
that drives an RC low-pass filter. The capacitor is not installed and a 0
Ω
resistor connects the op amp
output to the test-points. A filter can be installed by replacing the 0
Ω
resistor and installing a capacitor.
CAUTION
Only one shunt may be placed across each header. If more than one shunt is
placed across either JP1 or JP2, it will directly short two of the DAC analog
outputs together, possibly causing irreversible damage to the DAC8728.
The OFFSET-A and OFFSET-B analog outputs are routed to TP10 and TP17. The OFFSET feature can
only be used in bipolar mode. In unipolar mode, a shunt must be placed across JP8 and JP16 to connect
the OFFSET-x pins to the board ground.
V
MON
is the channel monitor output. It can relay any of the eight analog output signals, the OFFSET-A/B,
and the Ref Buffer A/B. The output pin has a 0.1
m
F capacitor connected. By default, the V
MON
pin is in
3-state mode.
7.2
Digital Control
The digital control signals can be applied directly to J1 (top or bottom side). The DAC8728EVM can also
be connected directly to a DSP or microcontroller interface board.
No specific evaluation software is provided with this EVM; however, various code examples are available
that show how to use this EVM with a variety of digital signal processors from Texas Instruments. Check
the specific device product folders on the
or send an e-mail to
for a
listing of available code examples. The EVM Gerber files are also available on request.
12
DAC8728EVM
SBAU161 – February 2010
Copyright © 2010, Texas Instruments Incorporated