MCP4431 Microchip Technology Inc., MCP4431 Datasheet - Page 45

• Manufacturer Part Number: MCP4431
• Description: 7/8-bit Volatile Quad Digital Pot With I 2c Interface
• Manufacturer: Microchip Technology Inc.

5.0
The Resistor Network has either 7-bit or 8-bit
resolution. Each Resistor Network allows zero scale to
full scale connections.
diagram for the resistive network of a device.
The Resistor Network is made up of several parts.
These include:
• Resistor Ladder
• Wiper
• Shutdown (Terminal Connections)
Devices have four resistor networks. These are
referred to as Pot 0, Pot 1 Pot 2, and Pot 3.
FIGURE 5-1:
 2010 Microchip Technology Inc.
R
Note 1:The wiper resistance is dependent on
AB
R
R
R
R
S
S
S
S
RESISTOR NETWORK
A
B
several factors including, wiper code,
device V
and W), and temperature.
Also for the same conditions, each tap
selection resistance has a small variation.
This R
some specifications (such as INL) for the
smaller
compared to larger resistance devices
(100.0 k).
R
R
R
R
R
W
W
W
W
W
W
(1)
(1)
(1)
(1)
(1)
DD
variation has greater effects on
resistance
(100h)
Resistor Block Diagram.
(FFh)
(FEh)
(01h)
(00h)
, Terminal voltages (on A, B,
8-Bit
256
N =
255
254
Analog Mux
1
0
Figure 5-1
(7Eh)
(80h)
(7Fh)
(01h)
(00h)
7-Bit
128
N =
127
126
devices
1
0
shows a block
(5.0 k)
W
5.1
The resistor ladder is a series of equal value resistors
(R
resistors. The total number of resistors in the series
(ladder) determines the R
1). The end points of the resistor ladder are connected
to analog switches which are connected to the device
Terminal A and Terminal B pins. The R
resistance has small variations over voltage and
temperature.
For an 8-bit device, there are 256 resistors in a string
between terminal A and terminal B. The wiper can be
set to tap onto any of these 256 resistors, thus
providing 257 possible settings (including terminal A
and terminal B).
For a 7-bit device, there are 128 resistors in a string
between terminal A and terminal B. The wiper can be
set to tap onto any of these 128 resistors, thus
providing 129 possible settings (including terminal A
and terminal B).
Equation 5-1
resistance.
EQUATION 5-1:
S
) with a connection point (tap) between the two
Resistor Ladder Module
R
R
S
S
=
=
shows the calculation for the step
-------------- -

--------------

128
R
256
R
AB
AB
MCP443X/5X


R
S
AB
CALCULATION
resistance (see
8-bit Device
7-bit Device
DS22267A-page 45
AB
(and R
Figure 5-
S
)