3

FN8223.2

January 30, 2009

Potentiometer Relationships

Principles of Operation

There are three sections of the X9C303: the input control,

counter and decode section; the nonvolatile memory; and the

resistor array. The input control section operates just like an

up/down counter. The output of this counter is decoded to turn

on a single electronic switch connecting a point on the resistor

array to the wiper output. Under the proper conditions, the

contents of the counter can be stored in nonvolatile memory

and retained for future use. The resistor array is comprised of

99 individual resistors connected in series. At either end of the

array and between each resistor is an electronic switch that

transfers the potential at that point to the wiper.

The wiper, when at either fixed terminal, acts like its

mechanical equivalent and does not move beyond the last

position. That is, the counter does not wrap around when

clocked to either extreme.

The electronic switches on the device operate in a “make

before break” mode when the wiper changes tap positions. If

the wiper is moved several positions, multiple taps are

significant amount if the wiper is moved several positions.

When the device is powered-down, the last counter position

stored will be maintained in the nonvolatile memory. When

power is restored, the contents of the memory are recalled

and the counter is reset to the value last stored.

Instructions and Programming

The INC, U/D and CS inputs control the movement of the

wiper along the resistor array. With CS set LOW, the device is

selected and enabled to respond to the U/D and INC inputs.

HIGH to LOW transitions on INC will increment or decrement

(depending on the state of the U/D input) a seven-bit counter.

The output of this counter is decoded to select one of

one-hundred wiper positions along the resistive array.

The value of the counter is stored in nonvolatile memory

whenever CS transitions HIGH while the INC input is also

HIGH.

The system may select the X9C303, move the wiper, and

deselect the device without having to store the latest wiper

position in nonvolatile memory. The wiper movement is

performed as previously described ; once the new position is

reached, the system would the keep INC LOW while taking

CS HIGH. The new wiper position would be maintained until

changed by the system or until a power-down/up cycle

recalled the previously stored data.

This would allow the system to always power-up to a preset

value stored in nonvolatile memory; then during system

operation minor adjustments could be made. The

adjustments might be based on user preference: system

parameter changes due to temperature drift, etc.

The state of U/D may be changed while CS remains LOW.

This allows the host system to enable the device and then

move the wiper up and down until the proper trim is attained.

Pin Names

SYMBOL

DESCRIPTION

VH

High Terminal (Potentiometer)

VW

Wiper Terminal (Potentiometer)

VL

Low Terminal (Potentiometer)

VSS

Ground

VCC

Supply Voltage

U/D

Up/Down Control Input

INC

Increment Control Input

CS

Chip Select Control Input

NC

No Connection

R99

R98

R2

R1

S100

S99

S98

S3

S2

S1

G

i

20Log

R

1

R

2

. . .

R

i

++

+

R

TOTAL

-------------------------------------------------

V

W

V

S

--------- V

L

0V

=

()

==

R

1

R

2

. . .

R

99

++

+

R

TOTAL

=

(REFER TEST CIRCUIT 1)

Mode Selection

CS

INC

U/D

MODE

L

H

Wiper Up

L

L

Wiper Down

H

X

Store Wiper Position

H

X

X

Standby Current

L

X

No Store, Return to Standby

L

H

Wiper Up (not recommended)

L

L

Wiper Down (not recommended)

X9C303