Digital Potentiometers

14

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VREGxNVREG: Data transfers from the volatile memory

register into the nonvolatile memory register.

Nonvolatile Memory

The internal EEPROM consists of a 16-bit nonvolatile

register that retains the value written to it prior to power

down. The nonvolatile register is programmed with the

midscale value at the factory. The nonvolatile memory

is guaranteed for 50 years for wiper position retention

and up to 200,000 wiper write cycles. A write-protect

feature prevents accidental overwriting of the EEPROM.

protect feature. The wiper position only updates with

to GND to allow EEPROM write cycles and to update

the wiper position from nonvolatile memory or directly

Power-Up

Upon power-up, the MAX5477/MAX5478/MAX5479

load the data stored in the nonvolatile memory register

into the volatile memory register, updating the wiper

position with the data stored in the nonvolatile memory

register. This initialization period takes 10µs.

Standby

The MAX5477/MAX5478/MAX5479 feature a low-power

standby mode. When the device is not being pro-

grammed, it enters into standby mode and supply cur-

rent drops to 500nA (typ).

Applications Information

The MAX5477/MAX5478/MAX5479 are ideal for circuits

requiring digitally controlled adjustable resistance,

such as LCD contrast control (where voltage biasing

adjusts the display contrast), or for programmable fil-

ters with adjustable gain and/or cutoff frequency.

Positive LCD Bias Control

Figures 9 and 10 show an application where the

MAX5477/MAX5478/MAX5479 provide an adjustable,

positive LCD bias voltage. The op amp provides buffer-

ing and gain to the resistor-divider network made by

the potentiometer (Figure 9) or by a fixed resistor and a

variable resistor (see Figure 10).

Programmable Filter

Figure 11 shows the MAX5477/MAX5478/MAX5479 in a

1st-order programmable application filter. Adjust the

Offset Voltage and Gain Adjustment

Connect the high and low terminals of one potentiome-

ter of a MAX5477 between the NULL inputs of a

MAX410 and the wiper to the op amp’s positive supply

to nullify the offset voltage over the operating tempera-

ture range. Install the other potentiometer in the feed-

back path to adjust the gain of the MAX410 (Figure 12).

Adjustable Voltage Reference

Figure 13 shows the MAX5477/MAX5478/MAX5479

used as the feedback resistors in multiple adjustable

voltage reference applications. Independently adjust

the output voltages of the MAX6160 parts from 1.23V to

MAX5477/MAX5478/MAX5479.

A

R

R

f

RC

C

=+

=

××

1

1

2

1

2

3

π

30V

5V

W_

H_

L_

MAX5477

MAX5478

MAX5479

MAX480

30V

5V

W_

H_

L_

MAX5477

MAX5478

MAX5479

MAX480

Figure 9. Positive LCD Bias Control Using a Voltage-Divider

Figure 10. Positive LCD Bias Control Using a Variable Resistor