MCP4921T-ESN MICROCHIP [Microchip Technology], MCP4921T-ESN Datasheet - Page 25

• Manufacturer Part Number: MCP4921T-ESN
• Manufacturer: MICROCHIP [Microchip Technology]

6.7
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 devel-
oped in Section 6.5.1 “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:
 2004 Microchip Technology Inc.
Designing A Double-Precision
DAC Using A Dual DAC
SPI™
V
V
REF
OUTA
V
O
3
MCP492X
MCP492X
=
=
V
V
DD
DD
V
V
-----------------------------------------------------
REFA
OUTA
Simple, Double-Precision DAC.
G
R
R
A
2
1
-------
2
D
+
+
DAC
V
V
DAC
12
A
OUTB
V
R
OUTA
OUTB
2
R
A
B
1
(Fine Adjust)
(Course Adjust)
>> R
R
1
V
2
OUTB
=
V
R
R
REFB
2
1
G
0.1 µF
B
-------
2
D
12
B
1.
2.
3.
4.
Calculate the resolution needed:
4.1V/1uV = 4.1e06. Since 2
resolution is desired. Since DNL = ±0.75 LSB,
this design can be attempted with the
MCP492X.
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 not perfectly
linear, as shown in the equation of Example 6-5.
2
B
V
V
is 100 , then R
‘s DNL error.
G = Gain select (1x or 2x)
D = Digital value of DAC (0 – 4096)
CC
CC
+
–
B
MCP4921/4922
‘s V
OUTB
1
V
has a resolution of 1 mV,
needs to be 100 k .
O
22
= 4.2e06, 22-bit
DS21897A-page 25
OUTA
by 1000