MCP433X datasheet(81/88 Pages) MICROCHIP

81 / 88 page

 2010 Microchip Technology Inc.

DS22242A-page 81

MCP433X/435X

FIGURE B-6:

Resistor Network Block

Diagram.

The characteristics of the wiper is determined by the

characteristics of the wiper switch at each of the

resistor networks tap points. Figure B-7 shows an

example of a wiper switch. As the device operational

voltage becomes lower, the characteristics of the wiper

switch change due to a lower voltage on the VG signal.

Figure B-7 shows an implementation of a wiper switch.

When the transistor is turned off, the switch resistance

is in the Giga

s. When the transistor is turned on, the

switch resistance is dependent on the VG, VW and

VWCn voltages. This resistance is referred to as RW.

FIGURE B-7:

Wiper Switch.

So looking at the wiper voltage (VW) for the

3.0V and 1.8V data gives the graphs in Figure B-8 and

Figure B-9. In the 1.8V graph, as the VW approaches

0.8V, the voltage increases nonlinearly. Since V = I * R,

and the current (IW) is constant, it means that the

device resistance increased nonlinearly at around

wiper code 160.

FIGURE B-8:

Wiper Voltage (VW) vs.

Wiper Code (VDD = 3.0V, IW = 190 µA).

FIGURE B-9:

Wiper Voltage (VW) vs.

Wiper Code (VDD = 1.8V, IW = 190 µA).

RW (1)

Note 1:

The wiper resistance is dependent on

several factors including, wiper code,

device VDD, Terminal voltages (on A, B

and W), and temperature.

RAB

NMOS

PMOS

Nn-1

Nn-2

Nn-3

VWC(n-2)

DVG

Note 1: Wiper Resistance (RW) depends on the

voltages at the wiper switch nodes

(VG, VW and VWCn).

RW (1)

NMOS

PMOS

NWC

Wiper

VG (VDD/VSS)

“gate”

VWCn

0.0

0.2

0.4

0.6

0.8

1.0

1.2

128 160 192 224 256

Wiper Code

-40C

+25C

+85C

+125C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

128 160 192 224 256

Wiper Code

-40C

+25C

+85C

+125C

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