MCP4012 Microchip Technology Inc., MCP4012 Datasheet - Page 39

• Manufacturer Part Number: MCP4012
• Description: Low-cost 64-step Volatile Digital Pot
• Manufacturer: Microchip Technology Inc.

6.1
6.1.1
When used as a rheostat, two of the three digital poten-
tiometer’s terminals are used as a resistive element in
the circuit. With terminal W (wiper) and either terminal
A or terminal B, a variable resistor is created. The
resistance will depend on the tap setting of the wiper
and the wiper’s resistance. The resistance is controlled
by changing the wiper setting.
The unused terminal (B or A) should be left floating.
Figure 6-2
used. Reversing the polarity of the A and B terminals
will not affect operation.
FIGURE 6-2:
This allows the control of the total resistance between
the two nodes. The total resistance depends on the
“starting” terminal to the wiper terminal. At the code
00h, the R
resistance in maximized (R
code 3Fh, the R
R
The resistance step size (R
resistor.
The change in wiper-to-end terminal resistance over
temperature is shown in
Figure 2-36
temperature will occur in the first few codes due to the
wiper
resistance. The remaining codes are dominated by the
total resistance tempco R
© 2006 Microchip Technology Inc.
BW
Note:
A
resistance in maximized (R
B
resistance
Resistor Configurations
BW
shows the two possible resistors that can be
RHEOSTAT CONFIGURATION
To avoid damage to the internal wiper
circuitry in this configuration, care should
be taken to insure the current flow never
exceeds 2.5 mA.
and
resistance is minimal (R
AW
Figure
W
resistance is minimal (R
coefficient
Rheostat Configuration.
2-48. The most variation over
AB
AB
S
) equates to one LSb of the
.
Figure
+ R
AB
W
affecting
). Conversely, at the
R
+ R
2-11,
Resistor
AW
W
W
), but the R
).
or
Figure
W
the
), but the
R
BW
2-24,
total
AW
6.1.2
When used as a potentiometer, all three terminals are
tied to different nodes in the circuit. This allows the
potentiometer to output a voltage proportional to the
input voltage. This configuration is sometimes called
voltage divider mode. The potentiometer is used to
provide a variable voltage by adjusting the wiper
position between the two endpoints as shown in
Figure
terminals will not affect operation.
FIGURE 6-3:
The temperature coefficient of the R
minimal by design. In this configuration, the resistors all
change uniformly, so minimal variation should be seen.
The wiper resistor temperature coefficient is different
from the R
node V
resistance, just the ratio of the R
temperature coefficient in most cases can be
ignored.
Note:
6-3. Reversing the polarity of the A and B
3
(Figure
AB
POTENTIOMETER
CONFIGURATION
To avoid damage to the internal wiper
circuitry in this configuration, care should
be taken to insure the current flow never
exceeds 2.5 mA.
temperature coefficient. The voltage at
MCP4011/2/3/4
6-3) is not dependent on this wiper
Potentiometer Configuration.
A
B
V
V
1
2
W
AB
DS21978C-page 39
resistors, so this
V
AB
3
resistors is