MCP4822-E/MS Microchip Technology, MCP4822-E/MS Datasheet - Page 22

• Manufacturer Part Number: MCP4822-E/MS
• Description: IC DAC 12BIT DUAL W/SPI 8MSOP
• Manufacturer: Microchip Technology

Specifications of MCP4822-E/MS

• Number Of Converters: 2
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Settling Time: 4.5µs
• Number Of Bits: 12
• Data Interface: Serial, SPI™
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Resolution: 12 bit
• Interface Type: Serial (3-Wire, SPI, Microwire)
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 2.7 V
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power Dissipation (max): -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

MCP4821/MCP4822
6.6
Bipolar operation is achievable using the MCP482X
devices by using an external operational amplifier (op
amp). This configuration is desirable due to the wide
variety and availability of op amps. This allows a gen-
eral purpose DAC, with its cost and availability advan-
tages, to meet almost any desired output voltage
range, power and noise performance.
EXAMPLE 6-3:
6.6.1
An output step magnitude of 1 mV, with an output range
of ±2.05V, is desired for a particular application.
1.
2.
3.
DS21953A-page 22
If R
Calculate the range: +2.05V – (-2.05V) = 4.1V.
Calculate the resolution needed:
4.1V/1 mV = 4100
Since 2
The amplifier gain (R
scale V
desired minimum output to achieve bipolar
operation. Since any gain can be realized by
choosing resistor values (R
value must be selected first. If a V
is used (G=2), solve for the amplifier’s gain by
setting the DAC to 0, knowing that the output
needs to be -2.05V. The equation can be
simplified to:
1
= 20 k and R
Bipolar Operation
DESIGN A BIPOLAR DAC USING
EXAMPLE 6-3
–
-------- -
12
R
OUT
R
1
2
= 4096, 12-bit resolution is desired.
=
(4.096V), must be equal to the
---------------- -
4.096V
–
2.05
V
V
V
2
SPI™
OUT
Digitally-Controlled Bipolar Voltage Source.
IN+
O
= 10 k , the gain will be 0.5
=
=
2
=
V
/R
IN+
V
------------------- -
3
R
2.048 G
1
OUT
3
), multiplied by full-
⎛
⎝
+
MCP482X
1
V
R
1
R
----- -
R
R
+
+R
DD
4
2
1
4
R
----- -
R
=
REF
2
1
2
-------
2
D
⎞
⎠
), the V
12
1
-- -
2
–
of 4.096V
V
DD
V
⎛
⎝
R
----- -
R
OUT
REF
2
1
⎞
⎠
R
3
R
4
V
G = Gain select (1x or 2x)
D = Digital value of DAC (0 – 4096)
DD
Example 6-3 illustrates a simple bipolar voltage source
configuration. R
while R
offset. Note that R4 can be tied to V
if a higher offset is desired. Note that a pull-up to V
could be used, instead of R
higher offset is desired.
4.
Next, solve for R
4096, knowing that the output needs to be
+2.05V.
R
1
3
---------------------- -
0.1 µF
R
and R
V
3
IN
R
+
If R
4
+
R
V
4
V
4
4
1
R
CC
CC
= 20 k , then R
and R
shift the DAC's output to a selected
2
=
+
–
2.05V
------------------------------------------------------ -
3
and R
2
© 2005 Microchip Technology Inc.
allow the gain to be selected,
1.5 4.096V
V
+
O
4
4
0.5 4.096V
or in addition to R
by setting the DAC to
3
= 10 k
DD
, instead of AV
=
2
-- -
3
4
, if a
SS
DD
,