MCP4013 Microchip Technology, MCP4013 Datasheet - Page 44

• Manufacturer Part Number: MCP4013
• Description: Low-Cost 64-Step Volatile Digital POT
• Manufacturer: Microchip Technology

MCP4011/2/3/4
8.0
Non-volatile digital potentiometers have a multitude of
practical uses in modern electronic circuits. The most
popular uses include precision calibration of set point
thresholds, sensor trimming, LCD bias trimming, audio
attenuation, adjustable power supplies, motor control
overcurrent trip setting, adjustable gain amplifiers and
offset trimming. The MCP4011/2/3/4 devices can be
used to replace the common mechanical trim pot in
applications where the operating and terminal voltages
are within CMOS process limitations (V
5.5V).
8.1
Applications that need accurate detection of an input
threshold event often need several sources of error
eliminated. Use of comparators and operational
amplifiers (op amps) with low offset and gain error can
help achieve the desired accuracy, but in many
applications, the input source variation is beyond the
designer’s control. If the entire system can be
calibrated after assembly in a controlled environment
(like factory test), these sources of error are minimized,
if not entirely eliminated.
Figure 8-1
configuration. This configuration is often referred to as
a “windowed voltage divider”. Note that R
not necessary to create the voltage divider, but their
presence is useful when the desired threshold has
limited range. It is “windowed” because R
narrow the adjustable range of V
less than V
magnitude of each output step is reduced. This
effectively increases the trimming resolution for a fixed
digital potentiometer resolution. This technique may
allow a lower-cost digital potentiometer to be utilized
(64 steps instead of 256 steps).
The MCP4011’s and MCP4013’s low DNL performance
is critical to meeting calibration accuracy in production
without having to use a higher precision digital
potentiometer.
EQUATION 8-1:
DS21978C-page 44
Where:
D
D = Digital Potentiometer Wiper Setting (0-63)
=
APPLICATIONS EXAMPLES
Set Point Threshold Trimming
⎛
⎝
DD
illustrates a common digital potentiometer
⎛
⎝
V
V
--------------
V
– V
TRIP
TRIP
DD
SS
R
⎞
⎠
R
=
WB
. If the output range is reduced, the
•
AB
(
V
(
CALCULATING THE
WIPER SETTING FROM
THE DESIRED V
DD
=
R
=
1
R
⎛
⎝
+
R
---------------------------------- -
R
AB
Nominal
R
1
R
AB
+
•
2
⎛
⎝
R
+
+
----- -
63
D
TRIP
AB
R
R
⎞
⎠
WB
2
+
) R
to a value much
R
–
2
⎞
⎠
DD
2
1
1
TRIP
)
and R
⎞
⎠
and R
= 2.7V to
•
63
2
2
can
are
FIGURE 8-1:
Potentiometer to Set a Precise Output Voltage.
8.1.1
If the application has to calibrate the threshold of a
diode, transistor or resistor, a variation range of 0.1V is
common. Often, the desired resolution of 2 mV or
better is adequate to accurately detect the presence of
a precise signal. A “windowed” voltage divider, utilizing
the MCP4011 or MCP4013, would be a potential
solution as shown in
FIGURE 8-2:
Calibration.
U/D
CS
MCP4011
R
U/D
R
CS
2
1
TRIMMING A THRESHOLD FOR AN
OPTICAL SENSOR
V
DD
MCP4011
B
A
W
V
0.1 µF
DD
Figure
Using the Digital
Set Point or Threshold
R
V
© 2006 Microchip Technology Inc.
sense
DD
V
A
B
TRIP
R
R
8-2.
1
2
W
Comparator
V
V
CC+
CC–
V
OUT
MCP6021