MCP40D17 Microchip Technology Inc., MCP40D17 Datasheet - Page 41

• 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.

6.0
The Resistor Network is made up of two parts. These
are:
• Resistor Ladder
• Wiper
Figure 6-1
network.
Digital potentiometer applications can be divided into
two resistor network categories:
• Rheostat configuration
• Potentiometer (or voltage divider) configuration
The MCP40D17 is a true rheostat, with terminal B and
the wiper (W) of the variable resistor available on pins.
The MCP40D18 device offers a voltage divider
(potentiometer) with terminal B internally connected to
ground.
The MCP40D19 device is a Rheostat device with
terminal A of the resistor floating, terminal B internally
connected to ground, and the wiper (W) available on
pin.
6.1
The resistor ladder is a series of equal value resistors
(R
resistors. The total number of resistors in the
series (ladder)
(see
are connected to the device Terminal A and Terminal B
pins. The R
over voltage and temperature.
The Resistor Network has 127 resistors in a string
between terminal A and terminal B. This gives 7-bits of
resolution.
The wiper can be set to tap onto any of these 127
resistors
(including terminal A and terminal B). This allows zero
scale to full scale connections.
A wiper setting of 00h connects the Terminal W (wiper)
to Terminal B (Zero Scale). A wiper setting of 3Fh is the
Mid scale setting. A wiper setting of 7Fh connects
the Terminal W (wiper) to Terminal A (Full Scale).
Table 6-1
Terminal A and B as well as the wiper W do not have a
polarity. These terminals can support both positive and
negative current.
© 2009 Microchip Technology Inc.
S
) with a connection point (tap) between the two
Figure
RESISTOR NETWORK
Resistor Ladder Module
illustrates the full wiper setting map.
thus
AB
shows a block diagram for the resistive
6-1). The end points of the resistor ladder
(and R
determines
providing
S
) resistance has small variations
128
the
possible
R
AB
resistance
settings
FIGURE 6-1:
Diagram.
TABLE 6-1:
Wiper Setting
Note 1: The wiper resistance is tap dependent.
07Eh - 040h
03Eh - 001h
R
R
R
R
S
S
S
S
07Fh
03Fh
000h
MCP40D17/18/19
A
B
N = 127
N = 126
N = 125
N = 1
N = 0
That is, each tap selection resistance
has a small variation. This variation has
more effect on devices with smaller R
resistance (5.0 kΩ).
WIPER SETTING MAP
Properties
Full Scale (W = A)
W = N
W = N (Mid Scale)
W = N
Zero Scale (W = B)
RW
RW
RW
RW
RW
Resistor Network Block
(1)
(1)
(1)
(1)
(1)
7Eh
7Fh
7Dh
01h
00h
Analog
Mux
DS22152B-page 41
W
AB