MCP40D17 Microchip Technology Inc., MCP40D17 Datasheet - Page 43

• Manufacturer Part Number: MCP40D17
• Description: 7-bit Single I 2 C? With Command Code Digital Pot With Volatile Memory In Sc70
• Manufacturer: Microchip Technology Inc.

6.2
6.2.1
When used as a rheostat, two of the three digital
potentiometer’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. So at the code
00h, the R
resistance in maximized (R
code 3Fh, the R
R
The resistance Step size (R
the resistor.
The pinout for the rheostat devices is such that as the
wiper register is incremented, the resistance of the
resistor will increase (as measured from Terminal B to
the W Terminal).
© 2009 Microchip Technology Inc.
BW
Note:
A
resistance in maximized (R
B
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.
resistance is minimal (R
AW
W
resistance is minimal (R
Rheostat Configuration.
AB
S
+ R
) equates to one LSb of
AB
W
). Conversely, at the
R
+ R
Resistor
AW
W
W
), but the R
).
or
W
), but the
R
BW
AW
6.2.2
When used as a potentiometer, all three terminals of
the device are tied to different nodes in the circuit. This
allows
proportional to the input voltage. This configuration is
sometimes
potentiometer is used to provide a variable voltage by
adjusting the wiper position between the two endpoints
as shown in
and B terminals will not affect operation.
FIGURE 6-3:
Configuration.
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
to the R
V
resistance, just the ratio of the R
temperature coefficient in most cases can be ignored.
3
Note:
(Figure
AB
the
MCP40D17/18/19
temperature coefficient. The voltage at node
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.
6-3) is not dependent on this Wiper
Figure
called
potentiometer
6-3. Reversing the polarity of the A
A
B
V
V
voltage
1
2
Potentiometer
to
W
divider
AB
output
DS22152B-page 43
resistors, so this
V
AB
3
mode.
resistors is
a
voltage
The