AD7303BRM Analog Devices Inc, AD7303BRM Datasheet - Page 8

• Manufacturer Part Number: AD7303BRM
• Description: IC DAC 8BIT DUAL R-R 8-MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7303BRM

• Rohs Status: RoHS non-compliant
• Settling Time: 1.2µs
• Number Of Bits: 8
• Data Interface: Serial
• Number Of Converters: 2
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 6.93mW
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,

AD7303
GENERAL DESCRIPTION
D/A Section
The AD7303 is a dual 8-bit voltage output digital-to-analog
converter. The architecture consists of a reference amplifier and
a current source DAC, followed by a current-to-voltage con-
verter capable of generating rail-to-rail voltages on the output of
the DAC. Figure 20 shows a block diagram of the basic DAC
architecture.
Both DAC A and DAC B outputs are internally buffered and
these output buffer amplifiers have rail-to-rail output character-
istics. The output amplifier is capable of driving a load of 10 k
to both V
selection for the DAC can be either internally generated from
V
selection is via a bit in the control register. The range on the
external reference input is from 1.0 V to V
voltage from either DAC is given by:
where:
Reference
The AD7303 has the facility to use either an external reference
applied through the REF pin or an internal reference generated
from V
where the internal V
When the internal reference is selected during the write to the
DAC, both switches are closed and V
applied to the reference amplifier. This internal V
appears at the reference pin as an output voltage for decoupling
purposes. When using the internal reference, external references
should not be connected to the REF Pin. This internal V
DD
V
N
REF
REF
or externally applied through the REF pin. Reference
DD
is the voltage applied to the external REF pin or
V
is the decimal equivalent of the code loaded to the DAC
register and ranges from 0 to 255.
V
DD
DD
DD
. Figure 21 shows the reference input arrangement
30k
0.1µF
30k
/2 when the internal reference is selected.
and ground and 100 pF to ground. The reference
REF
Figure 20. DAC Architecture
V
Figure 21. Reference Input
O
DD
A/B = 2
REFERENCE
AMPLIFIER
30k
30k
/2 has been selected.
V
CURRENT
DD
V
DAC
REF
AD7303
11.7k
DD
(N/256)
AD7303
/2 is generated and
REFERENCE
AMPLIFIER
INT/EXT
DD
11.7k
/2. The output
AMPLIFIER
OUTPUT
DD
/2 reference
DD
V
O
/2
A/B
–8–
reference appears at the reference pin as an output voltage for
decoupling purposes. When using the internal reference, external
references should not be connected to the REF pin. If external ref-
erence is selected, both switches are open and the externally
applied voltage to the REF pin is applied to the reference amplifier.
Decoupling capacitors applied to the REF pin decouple both
the internal reference and external reference. In noisy environ-
ments it is recommended that a 0.1 F capacitor be connected
to the REF pin to provide added decoupling even when the in-
ternal reference is selected.
Analog Outputs
The AD7303 contains two independent voltage output DACs
with 8-bit resolution and rail-to-rail operation. The output buffer
provides a gain of two at the output. Figures 3 to 5 show the sink
and source capabilities of the output amplifier. The slew rate of the
output amplifier is typically 8 V/ s and has a full-scale settling to 8
bits with a 100 pF capacitive load in typically 1.2 s.
The input coding to the DAC is straight binary. Table I shows
the binary transfer function for the AD7303. Figure 22 shows
the DAC transfer function for binary coding. Any DAC output
voltage can ideally be expressed as:
where:
N
V
REF
DAC INPUT
CODE
is the decimal equivalent of the binary input code.
N ranges from 0 to 255.
is the voltage applied to the external REF pin when
the external reference is selected and is V
internal reference is used.
Table I. Binary Code Table for AD7303 DAC
Digital Input
MSB . . . LSB
1111 1111
1111 1110
1000 0001
1000 0000
0111 1111
0000 0001
0000 0000
2.V
V
REF
REF
Figure 22. DAC Transfer Function
0
00
V
01
OUT
= 2
V
Analog Output
2
2
2
V
2
2
0 V
REF
7F
REF
(N/256)
255/256
254/256
129/256
127/256
V
80
V
REF
81
/256 V
V
V
V
V
REF
REF
REF
REF
DD
/2 if the
V
V
V
V
FE
REV. 0
FF