ad7303brm-reel Analog Devices, Inc., ad7303brm-reel Datasheet - Page 13

• Manufacturer Part Number: ad7303brm-reel
• Description: +2.7 V To +5.5 V, Serial Input, Dual Voltage Output 8-bit Dac
• Manufacturer: Analog Devices, Inc.

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Decoding Multiple AD7303
The SYNC pin on the AD7303 can be used in applications to
decode a number of DACs. In this application, all DACs in the
system receive the same serial clock and serial data, but only the
SYNC to one of the DACs will be active at any one time allow-
ing access to two channels in this eight-channel system. The
74HC139 is used as a 2- to 4-line decoder to address any of the
DACs in the system. To prevent timing errors from occurring,
the enable input should be brought to its inactive state while the
coded address inputs are changing state. Figure 33 shows a dia-
gram of a typical setup for decoding multiple AD7303 devices in
a system.
Figure 33. Decoding Multiple AD7303 Devices in a System
POWER
SCLK
SYNC
DATA
ADDRESS
Figure 32. AD7303 in Opto-Isolated Interface
ENABLE
CODED
SCLK
DIN
1G
1B
1A
74HC139
DGND
10k
10k
10k
V
V
DD
CC
V
V
V
DD
DD
DD
REGULATOR
1Y2
1Y0
1Y1
1Y3
+5V
SCLK
DIN
SYNC
AD7303
AGND
V
DD
SYNC
DIN
SCLK
SYNC
DIN
SCLK
SYNC
DIN
SCLK
SYNC
DIN
SCLK
V
V
AD7303
AD7303
OUT
OUT
AD7303
AD7303
10µF
REF
A
B
0.1µF
0.1µF
–13–
AD7303 as a Digitally Programmable Window Detector
A digitally programmable upper/lower limit detector using the
two DACs in the AD7303 is shown in Figure 34. The upper
and lower limits for the test are loaded to DACs A and B which,
in turn, set the limits on the CMP04. If a signal at the V
is not within the programmed window, a led will indicate the fail
condition.
Programmable Current Source
Figure 35 shows the AD7303 used as the control element of a
programmable current source. In this circuit, the full-scale cur-
rent is set to 1 mA. The output voltage from the DAC is applied
across the current setting resistor of 4.7 k in series with the
full-scale setting resistor of 470 . Suitable transistors to place
in the feedback loop of the amplifier include the BC107 and the
2N3904, which enable the current source to operate from a min
V
ating characteristics of the transistor. Suitable amplifiers in-
clude the AD820 and the OP295, both having rail-to-rail
operation on their outputs. The current for any digital input
code can be calculated as follows:
SYNC
SOURCE
SCLK
+5V
WITH V
0.1µF
AD780/ REF192
DIN
EXT
REF
GND
V
DD
Figure 34. Window Detector Using AD7303
IN
of 6 V. The operating range is determined by the oper-
Figure 35. Programmable Current Source
V
= +5V
OUT
0.1µF
REF
SYNC
DIN
SCLK
I = 2
INTERFACE
AD7303
SERIAL
GND
0.1µF
10µF
0.1µF
V
V
REF
V
DD
V
OUT
OUT
SCLK
DIN
SYNC
REF
B
A
10µF
D/(5E + 3
V
AD7303
DD
GND
V
V
DD
IN
= +5V
V
OUT
CMP04
A
1/2
256) mA
AD820/
OP295
+5V
AD7303
PASS/FAIL
FAIL
1/6 74HC05
1k
V
SOURCE
IN
input
LOAD
4.7k
PASS
470
1k