MCP4441-503EST datasheet(93/100 Pages) MICROCHIP

93 / 100 page

DS22265A-page 93

MCP444X/446X

FIGURE B-6:

Resistor Network Block

Diagram.

The characteristics of the wiper are 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

Ωs. 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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