MCP4822 As an example, if a similar application to the one Typical Schematic

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find MCP4822 datasheet
MCP4822 circuit
MCP4821 MCP4822
6.8
Designing A Double-Precision
DAC Using A Dual DAC
1.
Calculate the resolution needed:
4.1V/1 µV = 4.1e06. Since 2
22
= 4.2e06, 22-bit
resolution is desired. Since DNL = ±0.75 LSb,
this design can be attempted with the MCP482X
family.
Since DAC
B
‘s V
OUTB
has a resolution of 1 mV,
its output only needs to be “pulled” 1/1000 to
meet the 1 µV target. Dividing V
OUTA
by 1000
would allow the application to compensate for
B
‘s DNL error.
If R
2
is 100Ω, then R
1
needs to be 100 kΩ.
The resulting transfer function is shown in the
equation of Example 6-5.
Example 6-5 illustrates how to design a single-supply
voltage output capable of up to 24-bit resolution from a
dual 12-bit DAC This design is simply a voltage divider
with a buffered output.
As an example, if a similar application to the one
developed in
Section 6.6.1 “Design a Bipolar DAC
Using Example 6-3”
required a resolution of 1 µV
instead of 1 mV, and a range of 0V to 4.1V, then 12-bit
resolution would not be adequate.
2.
3.
4.
V
DD
A
(Fine Adjust)
V
OUTA
R
1
>> R
2
V
OUTB
R
2
0.1 µF
B
(Course Adjust)
SPI™
3
D
A
V
OUTA
=
2.048V
G
A
-------
12
2
V
OUTA
R
2
+
V
OUTB
R
1
V
O
= -----------------------------------------------------
R
1
+
R
2
D
B
V
OUTB
=
2.048V
G
B
-------
12
2
V
CC
+
V
O
R
1
MCP482X
V
DD
MCP482X
V
CC
G = Gain select (1x or 2x)
D = Digital value of DAC (0 – 4096)
EXAMPLE 6-5:
Simple, Double-Precision DAC
DS21953A-page 24
©
2005 Microchip Technology Inc.