MCP4017 datasheet(41/66 Pages) MICROCHIP

41 / 66 page

DS22147A-page 41

MCP4017/18/19

6.0

RESISTOR NETWORK

The Resistor Network is made up of two parts. These

are:

• Resistor Ladder

•Wiper

Figure 6-1 shows a block diagram for the resistive

network.

Digital potentiometer applications can be divided into

two resistor network categories:

• Rheostat configuration

• Potentiometer (or voltage divider) configuration

The MCP4017 is a true rheostat, with terminal B and

the wiper (W) of the variable resistor available on pins.

The MCP4018 device offers a voltage divider

(potentiometer) with terminal B internally connected to

ground.

The MCP4019 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

Resistor Ladder Module

The resistor ladder is a series of equal value resistors

(RS) with a connection point (tap) between the two

resistors. The total number of resistors in the series

(ladder) determines the RAB resistance (see Figure 6-

1). The end points of the resistor ladder are connected

to the device Terminal A and Terminal B pins. The RAB

(and RS) resistance has small variations 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 thus providing 128 possible settings

(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 illustrates the full wiper setting map.

Terminal A and B as well as the wiper W do not have a

polarity. These terminals can support both positive and

negative current.

FIGURE 6-1:

Resistor Network Block

Diagram.

TABLE 6-1:

WIPER SETTING MAP

Wiper Setting

Properties

07Fh

Full Scale (W = A)

07Eh - 040h

W = N

03Fh

W = N (Mid Scale)

03Eh - 001h

W = N

000h

Zero Scale (W = B)

N = 127

N = 126

N = 125

N = 1

N = 0

RW (1)

01h

Analog

Mux

RW (1)

00h

RW (1)

7Dh

RW (1)

7Eh

RW (1)

7Fh

Note 1: The wiper resistance is tap dependent.

That is, each tap selection resistance

has a small variation. This variation has

more effect on devices with smaller RAB

resistance (5.0 k

Ω).

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