Datasheet

DAC7512
14
SBAS156B
www.ti.com
FIGURE 10. Bipolar Operation with the DAC7512.
FIGURE 9. REF02 as Power Supply to DAC7512.
REF02
DAC7512
Three-Wire
Serial
Interface
+5V
135µA
V
OUT
= 0V to 5V
SYNC
SCLK
D
IN
+15
This is an output voltage range of ±5V with 000
H
correspond-
ing to a –5V output and FFF
H
corresponding to a +5V output.
LAYOUT
A precision analog component requires careful layout, ad-
equate bypassing, and clean, well-regulated power supplies.
As the DAC7512 offers single-supply operation, it will often
be used in close proximity with digital logic, microcontrollers,
microprocessors, and digital signal processors. The more
digital logic present in the design and the higher the switch-
ing speed, the more difficult it will be to achieve good
performance from the converter.
Due to the single ground pin of the DAC7512, all return
currents, including digital and analog return currents, must
flow through the GND pin. Ideally, GND would be connected
directly to an analog ground plane. This plane would be
separate from the ground connection for the digital compo-
nents until they were connected at the power entry point of
the system.
The power applied to V
DD
should be well regulated and low
noise. Switching power supplies and DC/DC converters will
often have high-frequency glitches or spikes riding on the
output voltage. In addition, digital components can create
similar high-frequency spikes as their internal logic switches
states. This noise can easily couple into the DAC output
voltage through various paths between the power connec-
tions and analog output. This is particularly true for the
DAC7512, as the power supply is also the reference voltage
for the DAC.
As with the GND connection, V
DD
should be connected to a
+5V power supply plane or trace that is separate from the
connection for digital logic until they are connected at the
power entry point. In addition, the 1µF to 10µF and 0.1µF
bypass capacitors are strongly recommended. In some situ-
ations, additional bypassing may be required, such as a
100µF electrolytic capacitor or even a “Pi” filter made up of
inductors and capacitors—all designed to essentially low-
pass filter the +5V supply, removing the high-frequency noise.
is loaded, the REF02 also needs to supply the current to the
load. The total current required (with a 5kΩ load on the DAC
output) is:
135µA + (5V/5kΩ) = 1.14mA
The load regulation of the REF02 is typically 0.005%/mA,
which results in an error of 285µV for the 1.14mA current
drawn from it. This corresponds to a 0.2LSB error.
BIPOLAR OPERATION USING THE DAC7512
The DAC7512 has been designed for single-supply operation
but a bipolar output range is also possible using the circuit in
Figure 10. The circuit shown will give an output voltage range
of ±5V. Rail-to-rail operation at the amplifier output is achiev-
able using an OPA340 as the output amplifier.
The output voltage for any input code can be calculated as
follows:
V
O
= V •
D
4096




•
R
1
+ R
2
R
1






– V
DD
•
R
2
R
1












where D represents the input code in decimal (0 - 4095).
With V
DD
= 5V, R
1
= R
2
= 10kΩ:
V
O
=
10•D
4096




– 5V
DAC7512
V
DD
V
OUT
R
1
10kΩ
R
2
10kΩ
Three-Wire
Serial
Interface
5V
10 F 0.1 F
—5V
–5V
+5V
OPA703