AD7393AN Analog Devices, AD7393AN Datasheet - Page 10

• Manufacturer Part Number: AD7393AN
• Description: +3 V/ Parallel Input Micropower 10- and 12-Bit DACs
• Manufacturer: Analog Devices

AD7392/AD7393
UNIPOLAR OUTPUT OPERATION
This is the basic mode of operation for the AD7392. As shown
in Figure 29, the AD7392 has been designed to drive loads as
low as 5 k in parallel with 100 pF. The code table for this
operation is shown in Table II.
Hexadecimal
Number
in DAC Register
FFF
801
800
7FF
000
The circuit can be configured with an external reference plus
power supply or powered from a single dedicated regulator
or reference depending on the application performance re-
quirements.
BIPOLAR OUTPUT OPERATION
Although the AD7393 has been designed for single-supply op-
eration, the output can be easily configured for bipolar opera-
tion. A typical circuit is shown in Figure 30. This circuit uses a
clean regulated +5 V supply for power, which also provides the
circuit’s reference voltage. Since the AD7393 output span swings
from ground to very near +5 V, it is necessary to choose an exter-
nal amplifier with a common-mode input voltage range that
extends to its positive supply rail. The micropower consump-
tion OP196 has been designed just for this purpose and results
in only 50 microamps of maximum current consumption. Con-
nection of the equal valued 470 k resistors results in a differen-
tial amplifier mode of operation with a voltage gain of two,
which produces a circuit output span of ten volts (that is, –5 V
to +5 V). As the DAC is programmed from zero-code 000
Figure 29. AD7392 Unipolar Output Operation
EXT
REF
DIGITAL INTERFACE
CIRCUITRY OMITTED
FOR CLARITY
0.01 F
Table II. Unipolar Code Table
20
Decimal
Number
in DAC Register
4095
2049
2048
2047
0
R
REF
+2.7V TO +5.5V
AGND/DGND
AD7392
V
DD
17, 18
1
V
OUT
19
R
0.1 F
L
5k
Output
Voltage (V)
V
2.4994
1.2506
1.2500
1.2494
0
REF
C
10 F
L
= 2.5 V
100pF
H
to
–10–
midscale 200
is set at –5 V, 0 V and +5 V (minus 1 LSB). The output voltage
V
where D is the decimal code loaded in the AD7393 DAC regis-
ter. Note that the LSB step size is 10/1024 = 10 mV. This cir-
cuit has been optimized for micropower consumption including
the 470 k gain setting resistors, which should have low tem-
perature coefficients to maintain accuracy and matching (prefer-
ably the same resistor material, such as metal film). If better
stability is required, the power supply could be substituted with
a precision reference voltage such as the low drop out REF195,
which can easily supply the circuit’s 162 A of current, and still
provide additional power for the load connected to V
micropower REF195 is guaranteed to source 10 mA output
drive current, but only consumes 50 A internally. If higher
resolution is required, the AD7392 can be used with the addi-
tion of two more bits of data inserted into the software coding,
which would result in a 2.5 mV LSB step size. Table III shows
examples of nominal output voltages V
Operation circuit application.
Hexadecimal
Number
In DAC Register
3FF
201
200
1FF
000
O
+5V
is coded in offset binary according to Equation 4.
DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY
C
I
SY
< 162 A
V
Figure 30. Bipolar Output Operation
H
O
REF
to full scale 3FF
AD7393
Table III. Bipolar Code Table
<2 A
512
GND
D
– 1
V
DD
Decimal
Number
in DAC Register
1023
513
512
511
0
<100 A
V
470k
OUT
5
H
, the circuit output voltage V
470k
OP196
O
–5V
provided by the Bipolar
<50 A
Analog
Output
Voltage (V)
4.9902
0.0097
0.0000
–0.0097
–5.0000
V
O
Equation 4
+5V
–5V
O
. The
BIPOLAR
OUTPUT
SWING
REV. A
O