AD7303 Analog Devices, AD7303 Datasheet - Page 12

• Manufacturer Part Number: AD7303
• Description: +2.7 V to +5.5 V, Serial Input, Dual Voltage Output 8-Bit DAC
• Manufacturer: Analog Devices

Specifications of AD7303

• Resolution (bits): 8bit
• Dac Update Rate: 833kSPS
• Dac Settling Time: 1.2µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

AD7303
AD7303 to Microwire Interface
Figure 29 shows an interface between the AD7303 and any
microwire compatible device. Serial data is shifted out on the
falling edge of the serial clock and is clocked into the AD7303
on the rising edge of the SK.
APPLICATIONS
Typical Application Circuit
Figure 30 shows a typical setup for the AD7303 when using an
external reference. The reference range for the AD7303 is from
1 V to V
but will saturate the output at both the top and bottom end of
the transfer function. From input to output on the AD7303
there is a gain of two. Suitable references for 5 V operation are
the AD780 and REF192. For 3 V operation, a suitable external
reference would be the AD589, a 1.23 V bandgap reference.
The AD7303 can also be used with its own internally derived
V
bit of the 16-bit input word. The internal reference, when
selected, is also provided as an output at the REF pin and can
be decoupled at this point with a 0.1 F capacitor for noise
reduction purposes. AC references can also be applied as exter-
nal references to the AD7303. The AD7303 has limited multi-
plying capability, and a multiplying bandwidth of up to 10 kHz
is achievable.
DD
*ADDITIONAL PINS OMITTED FOR CLARITY
/2 reference. Reference selection is through the INT/EXT
MICROWIRE*
AD589 WITH V
Figure 30. AD7303 Using External Reference
DD
WITH V
AD780/ REF192
Figure 29. AD7303 to Microwire Interface
EXT
REF
/2 V. Higher values of reference can be incorporated
GND
OR
V
DD
IN
= +5V
V
DD
OUT
SK
SO
CS
= +3V
INTERFACE
SERIAL
0.1µF
0.1µF
SCLK
DIN
SYNC
REF
10µF
V
DD
AD7303
= +3V TO +5V
GND
V
DD
SCLK
DIN
SYNC
V
V
AD7303*
OUT
OUT
A
B
–12–
Bipolar Operation Using the AD7303
The AD7303 has been designed for single supply operation, but
bipolar operation is achievable using the circuit shown in Figure
31. The circuit shown has been configured to achieve an output
voltage range of –5 V < V
amplifier output is achievable using an AD820 or OP295 as the
output amplifier.
The output voltage for any input code can be calculated as
follows:
V
where
and
With V
V
Opto-Isolated Interface for Process Control Applications
The AD7303 has a versatile 3-wire serial interface making it
ideal for generating accurate voltages in process control and
industrial applications. Due to noise, safety requirements or dis-
tance, it may be necessary to isolate the AD7303 from the con-
troller. This can easily be achieved by using opto-isolators,
which will provide isolation in excess of 3 kV. The serial loading
structure of the AD7303 makes it ideally suited for use in opto-
isolated applications. Figure 32 shows an opto-isolated interface
to the AD7303 where DIN, SCLK and SYNC are driven from
opto-couplers. In this application the reference for the AD7303
is the internal V
pin with a 0.1 F ceramic capacitor for noise reduction purposes.
O
DD
AD589 WITH V
D is the decimal equivalent of the code loaded to the DAC
V
= [(1+R4/R3)*(R2/(R1+R2)*(2*V
REF
WITH V
AD780/ REF192
= 5 V.
Figure 31. Bipolar Operation Using the AD7303
EXT
REF
REF
is the reference voltage input.
GND
OR
V
DD
IN
= 2.5 V, R1 = R3 = 10 k and R2 = R4 = 20K and
= +5V
DD
V
OUT
= +3V
DD
INTERFACE
/2 reference. It is being decoupled at the REF
SERIAL
V
0.1µF
0.1µF
OUT
O
= (10
SCLK
DIN
SYNC
< +5 V. Rail-to-rail operation at the
REF
10µF
AD7303
V
DD
GND
V
DD
D/256) – 5
= +5V
V
OUT
10k
REF
R3
A
*D/256)] – R4*V
10k
R1
20k
R4
R2
20k
–5V
+5V
REV. 0
REF
/R3
5V