Digital Potentiometers

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the wiper among the 256 tap points (Figure 2). A non-

volatile memory stores the wiper position and recalls

the stored wiper position upon power-up. The non-

volatile memory is guaranteed for 50 years for wiper

data retention and up to 200,000 wiper store cycles.

Analog Circuitry

The MAX5477/MAX5478/MAX5479 consist of two resistor

arrays with 255 resistive elements; 256 tap points are

accessible to the wipers, along the resistor string

between H_ and L_. The wiper tap point is selected by

face. An address byte, a command byte, and 8 data bits

program the wiper position for each potentiometer. The

H_ and L_ terminals of the MAX5477/MAX5478/

MAX5479 are similar to the two end terminals of a

mechanical potentiometer. The MAX5477/MAX5478/

MAX5479 feature power-on reset circuitry that loads the

wiper position from the nonvolatile memory at power-up.

Digital Interface

The MAX5477/MAX5478/MAX5479 feature an internal,

nonvolatile EEPROM that stores the wiper state for ini-

tialization during power-up. The shift register decodes

the command and address bytes, routing the data to

the proper memory registers. Data written to a volatile

memory register immediately updates the wiper posi-

tion, or writes data to a nonvolatile register for storage

(see Table 2).

The volatile register retains data as long as the device

is powered. Removing power clears the volatile regis-

ter. The nonvolatile register retains data even after

power is removed. Upon power-up, the power-on reset

circuitry controls the transfer of data from the non-

volatile register to the volatile register.

A write-protect feature prevents accidental overwriting

prevent any EEPROM write cycles. The wiper register

only updates with the value in the EEPROM when WP =

SDA

SCL

S

START

CONDITION

P

STOP

CONDITION

Figure 3. Start and Stop Conditions

MSB

START

SCL

SDA

ACK

A0

A2

A1

101

0

LSB

NOP/W

Figure 4. Slave Address

256-POSITION

DECODER

H_

L_

W_

WIPER

CODE 02h

Figure 2. Potentiometer Configuration