AD7804 Analog Devices, AD7804 Datasheet - Page 19

• Manufacturer Part Number: AD7804
• Description: +3.3 V to +5 V Quad/Octal 10-Bit DAC
• Manufacturer: Analog Devices

Specifications of AD7804

• Resolution (bits): 10bit
• Dac Update Rate: 667kSPS
• Dac Settling Time: 1.5µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser

REV. A
Figure 26. Sub DAC Output Voltage vs. DAC Input Codes
(HEX) for Offset Binary Coding
Configuring the AD7804/AD7808 for Offset Binary Coding
Figure 27 shows a typical configuration for the AD7804/AD7808.
This circuit can be used for both 3.3 V or 5 V operation and
uses an external AD589 as the reference for the part and serial
interfacing with offset binary coding is used. The MX1 and
MX0 bits in the system control register have to be set to enable
selection of the AD589 as the reference. The following are the
steps required to operate the DACs in this part. Figures 4 to 7
show the contents of the registers on the AD7804/AD7808.
DAC INPUT CODE
Table IX. Offset Binary Code Table for Sub DAC
127
128
Digital Input
MSB . . . LSB
11111111
11111110
10000001
10000000
01111111
00000001
00000000
V
V
BIAS
32
BIAS
32
0
00
01
Analog Output
V
V
V
0
–V
–V
–V
BIAS
BIAS
BIAS
BIAS
BIAS
BIAS
7F 80
/16
/16
/16
/16
/16
/32
81
127/256
126/256
1/256
1/256
127/256
FE
FF
–19–
System Control Register Serial Write:
Channel Control Register Serial Write:
Main DAC Data Register Serial Write:
Sub DAC Data Register Serial Write:
Table VIII and Figure 25 show the analog outputs available for
the above configuration when writing to the Main DAC only
while Table IX and Figure 26 show the contributions from the
Sub DAC to the overall transfer function. The total output for a
single channel when using offset binary coding is the sum of that
from the Main DAC and the Sub DAC.
V
where NA ranges from 0 to +1023 and NB ranges from 0 to
+255. Figure 28 shows a pictorial view of the transfer function
for any DAC channel.
Figure 27. Typical Configuration for AD7804/AD7808
Using an AD589 1.23 V Reference for the AD7804/AD7808
OUT
Write 0060 Hex Mode bits select system control register
Write 4210 Hex
Write 23FF Hex
Write A3FF Hex This 16-bit write selects writing to channel
= V
= V
=
= V
INTERFACE
AD7804/AD7805/AD7808/AD7809
0.01 F
0.01 F
SERIAL
DV
4096)
BIAS
OUT
BIAS
[(NB-128)/256]
DD
' + V
+ 1.875 V
10 F
(1 + 1.875
OUT
and configure system for offset binary
coding and normal operation.
channel A is configured for operation with
external reference.
This 16-bit write selects writing to channel
A and writes full scale to the Main DAC.
A Sub DAC and writes full scale to the
Sub DAC.
Mode bits select channel control register,
"
COMP
SDIN
CLKIN
CLR
LDAC
FSIN
0.1 F
BIAS
+3.3V/+5V
DGND
AV
AD7804/
AD7808
((NA-512)/1024) + (NB-128)/
DD
((NA-512)/1024) + V
DV
AGND
DD
REFOUT
REFIN
V
V
V
V
OUT
OUT
OUT
OUT
A
B
C
D
0.1 F
6.8k
AD589
BIAS
/16