MCP4821T-E/P MICROCHIP [Microchip Technology], MCP4821T-E/P Datasheet - Page 24

• Manufacturer Part Number: MCP4821T-E/P
• Manufacturer: MICROCHIP [Microchip Technology]

MCP4821/MCP4822
6.8
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.
EXAMPLE 6-5:
DS21953A-page 24
Designing A Double-Precision
DAC Using A Dual DAC
V
OUTA
V
SPI™
O
=
=
2.048V G
V
-----------------------------------------------------
OUTA
3
MCP482X
MCP482X
Simple, Double-Precision DAC.
V
V
DD
DD
R
R
2
1
+
+
A
D
-------
2
V
R
12
OUTB
2
A
DAC
V
V
DAC
OUTB
OUTA
R
1
R
A
B
V
1
(Fine Adjust)
(Course Adjust)
OUTB
>> R
2
=
2.048V G
R
R
2
1
B
D
-------
2
12
1.
2.
3.
4.
B
0.1 µF
Calculate the resolution needed:
4.1V/1 µV = 4.1e06. Since 2
resolution is desired. Since DNL = ±0.75 LSb,
this design can be attempted with the MCP482X
family.
Since DAC
its output only needs to be “pulled” 1/1000 to
meet the 1 µV target. Dividing V
would allow the application to compensate for
DAC
If R
The resulting transfer function is shown in the
equation of Example 6-5.
2
B
G = Gain select (1x or 2x)
is 100 , then R
D = Digital value of DAC (0 – 4096)
‘s DNL error.
V
V
B
CC
CC
‘s V
+
–
OUTB
© 2005 Microchip Technology Inc.
1
has a resolution of 1 mV,
needs to be 100 k .
V
O
22
= 4.2e06, 22-bit
OUTA
by 1000