ad7393 Analog Devices, Inc., ad7393 Datasheet - Page 15

• Manufacturer Part Number: ad7393
• Description: 3 V, Parallel Input Micropower 10-/12-bit Dacs
• Manufacturer: Analog Devices, Inc.

BIPOLAR OUTPUT OPERATION
Although the AD7393 is designed for single-supply operation,
the output can be easily configured for bipolar operation. A
typical circuit is shown in Figure 33. 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 external
amplifier with a common-mode input voltage range that extends
to its positive supply rail. The micropower consumption OP196
is designed just for this purpose and results in only 50 μA of
maximum current consumption. Connecting the two 470 kΩ
resistors results in a differential amplifier mode of operation
with a voltage gain of 2, which produces a circuit output span
of 10 V, that is, −5 V to +5 V. As the DAC is programmed from
zero-code 0x000 to midscale 0x200 to full scale 0x3FF, the circuit
output voltage, V
The output voltage, V
Equation 4.
where D is the decimal code loaded in the AD7393 DAC
register.
Note that the LSB step size is 10/1024 = 10 mV. This circuit
is optimized for micropower consumption including the 470 kΩ
gain setting resistors, which should have low temperature
coefficients to maintain accuracy and matching (preferably the
same resistor material, such as metal film).
If better stability is required, the power supply may be substi-
tuted with a precision reference voltage such as the low dropout
REF195, which can easily supply the circuit’s 162 μA of current,
and still provide additional power for the load connected to V
The micropower REF195 is guaranteed to source 10 mA output
drive current, but consumes only 50 μA internally.
V
O
=
⎡
⎢ ⎣
512
D
−
O
1
, is set at −5 V, 0 V, and +5 V (minus 1 LSB).
⎤
⎥ ⎦
×
O
5
, is coded in offset binary according to
Rev. C | Page 15 of 20
(4)
O
.
If higher resolution is required, the AD7392 can be used with
two additional bits of data inserted into the software coding,
which results in a 2.5 mV LSB step size. Table 8 shows examples
of nominal output voltages (V
operation circuit application.
Table 8. Bipolar Code Table
Hexadecimal
0x3FF
0x201
0x200
0x1FF
0x000
+5V
NOTES
1. DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY
C
DAC Register No.
I
SY
<162µA
V
REF
AD7393
Figure 33. Bipolar Output Operation
<2µA
GND
Decimal
1023
513
512
511
0
V
DD
V
470kΩ
<100µA
OUT
O
) provided by the bipolar
Analog Output Voltage (V)
+4.9902
+0.0097
0.0000
−0.0097
−5.0000
470kΩ
AD7392/AD7393
OP196
–5V
<50µA
V
O
+5V
–5V
BIPOLAR
OUTPUT
SWING