MCP4562 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

MCP4562

7-Bit Single I²C™ Digital POT with Volatile Memory in SC70

Microchip Technology 

6.2 Resistor Configurations

6.2.1 RHEOSTAT CONFIGURATION

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 shows the two possible resistors that can be

used. Reversing the polarity of the A and B terminals

will not affect operation.

A

W

B

RAW or RBW

Resistor

FIGURE 6-2:

Rheostat Configuration.

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 RBW resistance is minimal (RW), but the RAW

resistance in maximized (RAB + RW). Conversely, at the

code 3Fh, the RAW resistance is minimal (RW), but the

RBW resistance in maximized (RAB + RW).

The resistance Step size (RS) equates to one LSb of

the resistor.

Note:

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.

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).

MCP4017/18/19

6.2.2

POTENTIOMETER

CONFIGURATION

When used as a potentiometer, all three terminals of

the device 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 6-3. Reversing the polarity of the A

and B terminals will not affect operation.

V1

A

W V3

B

V2

FIGURE 6-3:

Configuration.

Potentiometer

The temperature coefficient of the RAB resistors is

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 RAB temperature coefficient. The voltage at node

V3 (Figure 6-3) is not dependent on this Wiper

resistance, just the ratio of the RAB resistors, so this

temperature coefficient in most cases can be ignored.

Note:

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.

© 2009 Microchip Technology Inc.

DS22147A-page 43

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