AD7226 Analog Devices, AD7226 Datasheet - Page 8

• Manufacturer Part Number: AD7226
• Description: LC2MOS Quad 8-Bit D/A Converter
• Manufacturer: Analog Devices

AD7226
Unipolar Output Operation
This is the basic mode of operation for each channel of the
AD7226, with the output voltage having the same positive
polarity as +V
(V
section which outlines the advantages of having negative V
The code table for unipolar output operation is shown in Table
II. Note that the voltage at V
spect to DGND in order to prevent parasitic transistor turn-on.
Connections for the unipolar output operation are shown in Fig-
ure 12.
Bipolar Output Operation
Each of the DACs of the AD7226 can be individually config-
ured to provide bipolar output operation. This is possible using
one external amplifier and two resistors per channel. Figure 13
shows a circuit used to implement offset binary coding (bipolar
Note: 1 LSB
SS
DAC Latch Contents
MSB
1 1 1 1
1 0 0 0
1 0 0 0
0 1 1 1
0 0 0 0
0 0 0 0
= AGND) or with positive/negative supplies (see op-amp
Figure 12. AD7226 Unipolar Output Circuit
1 1 1 1
0 0 0 1
0 0 0 0
1 1 1 1
0 0 0 1
0 0 0 0
LSB
REF
Table II. Unipolar Code Table
V
. The AD7226 can be operated single supply
REF
2
8
REF
V
REF
must never be negative with re-
256
Analog Output
0 V
1
V
V
V
V
V
REF
REF
REF
REF
REF
256
129
256
128
256
127
256
256
255
1
V
REF
2
SS
).
–8–
operation) with DAC A of the AD7226. In this case
Mismatch between R1 and R2 causes gain and offset errors and
therefore these resistors must match and track over temperature.
Once again the AD7226 can be operated in single supply or
from positive/negative supplies. Table III shows the digital code
versus output voltage relationship for the circuit of Figure 13
with R1 = R2.
AGND BIAS
The AD7226 AGND pin can be biased above system GND
(AD7226 DGND) to provide an offset “zero” analog output
voltage level. Figure 14 shows a circuit configuration to achieve
this for channel A of the AD7226. The output voltage, V
can be expressed as:
With R1 = R2
where D
latch A.
V
where D
word (0
DAC Latch Contents
MSB
1 1 1 1
1 0 0 0
1 0 0 0
0 1 1 1
0 0 0 0
0 0 0 0
OUTA
Table III. Bipolar (Offset Binary) Code Table
= V
Figure 13. AD7226 Bipolar Output Circuit
V
A
A
OUT
is a fractional representation of the digital word in
is a fractional representation of the digital input
D
BIAS
1 1 1 1
0 0 0 1
0 0 0 0
1 1 1 1
0 0 0 1
0 0 0 0
+ D
255/256).
LSB
1
V
A
OUT
R2
R1
(V
IN
= (2 D
)
D
A
V
A
REF
– 1) • V
Analog Output
0 V
–V
–V
–V
–
V
V
REF
REF
REF
REF
REF
R2
R1
REF
127
128
128
128
127
128
128
128
1
1
V
REF
–V
REF
OUTA
REV. A
,