WMS7140/1

Publication Release Date: April 21, 2005

- 7 - Revision 1.1

7. FUNCTIONAL DESCRIPTION

The WMS7140/1, a nonvolatile digitally programmable potentiometers with 16 taps, with or without

output buffer, is designed to operate as both a potentiometer or a variable resistor depending upon

the output configuration selected.

The chip can store up to one 8-bit word in a nonvolatile memory (NVMEM0) in order to set the tap

The WMS7140/1 is controlled by a serial Up-Down (3-wire) interface that allows setting the tap

7.1. POTENTIOMETER AND RHEOSTAT MODES

The WMS7140/1 can operate as either a rheostat or as a potentiometer (voltage divider). When in the

potentiometer configuration there are two possible modes. One is done using WMS7140 Winpot

device without the output buffer and the other mode is done with WMS7141 WinPot device with the

output buffer.

7.1.1. Rheostat Configuration

The WMS7140/1 acts as a two terminal resistive element in the rheostat configuration where one

terminal can be connected to either the end point pins of the resistor (V

and V

) and the other

terminal is the wiper (V

) pin. This configuration controls the resistance between the two terminals

and the resistance can be adjusted by sending the corresponding tap register setting to the

WMS7140/1 or can also be set by loading a pre-set tap register value from nonvolatile memory

NVMEM0 upon power up.

7.1.2. Potentiometer Configuration

In potentiometer configuration an input voltage is applied to either one of the end point pins (V

or V

The voltage on the wiper pin will be proportional to the voltage difference between V

and V

and the

wiper setting. The resistance cannot be directly measured in this configuration.

7.2. NON-VOLATILE MEMORY (NVMEM)

The WMS7140/1 has one NVMEM position available for storing the potentiometer setting. The

NVMEM position can be directly written via the Up/Down interface. The potentiometer is loaded with

the value stored in the NVMEM0 on power up.

WMS7140/1

- 8 -

7.3.

SERIAL DATA INTERFACE

The Up/Down family has a 3-wire Serial Data Interface consisting of CS , INC , U/

pins. Only

UP/DOWN operations can be performed. The key features of this interface include:

• Increment/Decrement operations on the tap register (TR)

• Direct refresh of tap register (TR) from internal NVMEM

• Nonvolatile storage of the present tap register value into the NVMEM and automatic recall at

power up

• For WMS7141 devices, output buffer amplifier

7.4. OPERATION OVERVIEW

The wiper position or the Tap Register(TR) setting can only be changed by the UP/DOWN operation

with the combination of

, U/D , and

INC

signals. When

is low, the part will be activated and

the TR setting can be changed by toggling

INC , and TR will move up when U/ D is High and move

down when U/

is Low. The TR setting will be stored into the user NVMEM automatically each time

CS goes high while INC holds high. Otherwise, if INC is low when CS goes high, the TR setting

will not be stored. The NVMEM content will be automatically loaded into TR at Power On. The user

NVMEM can be tested through the voltage measurement on the wiper pin after saving TR setting into

the NVMEM and reloading into the TR. When the TR setting is already at LOW, further DOWN

operations won’t change the setting. Similarly, when TR setting is at HIGH, further UP operations

won’t change the setting.

When

CS is held HIGH, the part will be in Standby mode and the TR setting will not be changed.

The operating modes of Up/Down are summarized below.

D INC

Operation

Low High High to Low Wiper toward V

Low Low High to Low Wiper toward V

Low to High x High Store Wiper Position

Low to High x Low No Store, Return to Standby

High x x Standby

Note: x means don’t care

WMS7140/1

Publication Release Date: April 21, 2005

- 9 - Revision 1.1

8. TIMING DIAGRAMS

Conditions: V

= +2.7V to 5.5V, V

= V

, V

= 0V, T = 25°C

FIGURE 3 –WMS7140/1 TIMING DIAGRAM

Note:

[1] MI in the AC Timing diagram (Figure 3) refers to the minimum incremental change in the wiper output due to a change in the

wiper position.

INC

[1]

90%

(

store

)

CPH

Part #	141050
Description	TYPE I 42VDC 50 AMPAUTO RESET PANEL MOUNT
Category	CIRCUIT BREAKER
Availability	Available With Additional Lead Time
Qty	199

Qty	Price
1 - 99	$27.52750
100 - 999	$20.59904
1,000 - 4,999	$18.90504
5,000 - 9,999	$17.56678
10,000 +	$11.61600

141050

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