AD7398 Analog Devices, AD7398 Datasheet - Page 19

• Manufacturer Part Number: AD7398
• Description: Quad, Serial-Input 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of AD7398

• Resolution (bits): 12bit
• Dac Update Rate: 167kSPS
• Dac Settling Time: 6µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

PROGRAMMABLE DAC REFERENCE VOLTAGE
With the flexibility of the AD7398/AD7399, one of the internal
DACs can be used to control a common programmable V
for the remainder of the DACs.
The circuit configuration is shown in Figure 37. The relationship of
V
R1 and R2, and is given by
where:
D = decimal equivalent of input code.
N = number of bits.
V
V
REF
REFX
REFX
= applied external reference.
V
V
= reference voltage for DAC A to DAC D.
to V
REFX
REFX
REF
=
=
V
is dependent upon the digital code and the ratio of
V

 

REF
REF
1
+
×
×
2
D
 +


 +


N
1
1
×
R
R
R
R
R
R
2
1
2
1
2
1







 

−
V
REFX
×
2
D
N
×
R
R
2
1
DAC A
DAC B
DAC C
DAC D
V
V
V
V
REF
REF
REF
REF
AD7398/AD7399
A
B
C
D
Figure 37. Programmable DAC Reference
REFX
Rev. C | Page 19 of 24
(4)
(5)
V
V
V
V
OUT
OUT
OUT
OUT
A
B
C
D
VIN
Table 7. V
R1, R2
R1 = R2
R1 = R2
R1 = R2
R1 = 3R2
R1 = 3R2
R1 = 3R2
The accuracy of V
Therefore, tight tolerance, low tempco, thin film resistors
should be used.
R1 ±0.1%
TO OTHER
COMPONENTS
ADR293
R2 ±0.1%
REFX
V
REF
vs. R1 and R2
REFX
Digital Code
0000 0000 0000
1000 0000 0000
1111 1111 1111
0000 0000 0000
1000 0000 0000
1111 1111 1111
is affected by the quality of R1 and R2.
AD7398/AD7399
V
2 V
1.3 V
V
4 V
1.6 V
V
REF
REF
REFX
REF
REF
REF
REF