AD7398 查看數據表（PDF） - Analog Devices
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AD7398 Datasheet PDF : 24 Pages
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PROGRAMMABLE DAC REFERENCE VOLTAGE
With the flexibility of the AD7398/AD7399, one of the internal
DACs can be used to control a common programmable VREFX
for the remainder of the DACs.
The circuit configuration is shown in Figure 37. The relationship of
VREFX to VREF is dependent upon the digital code and the ratio of
R1 and R2, and is given by
VREFX
= VREF
× 1 +
R2
R1
−
VREFX
×
D
2N
×
R2
R1
(4)
VREFX
=
VREF
×
1
+
1 +
D
2N
×
R2
R1
R2
R1
(5)
where:
D = decimal equivalent of input code.
N = number of bits.
VREF = applied external reference.
VREFX = reference voltage for DAC A to DAC D.
AD7398/AD7399
Table 7. VREFX vs. R1 and R2
R1, R2
Digital Code
R1 = R2
0000 0000 0000
R1 = R2
1000 0000 0000
R1 = R2
1111 1111 1111
R1 = 3R2
0000 0000 0000
R1 = 3R2
1000 0000 0000
R1 = 3R2
1111 1111 1111
VREFX
2 VREF
1.3 VREF
VREF
4 VREF
1.6 VREF
VREF
The accuracy of VREFX is affected by the quality of R1 and R2.
Therefore, tight tolerance, low tempco, thin film resistors
should be used.
AD7398/AD7399
R2 ±0.1%
VREFA
DAC A
VREFB
DAC B
VOUTA
R1 ±0.1%
VREF
VIN ADR293
VOUTB
VREFC
DAC C
VOUTC
TO OTHER
COMPONENTS
VREFD
DAC D
VOUTD
Figure 37. Programmable DAC Reference
Rev. C | Page 19 of 24
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