Digital Potentiometers

12

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ADDRESS BYTE

CONTROL BYTE

DATA BYTE

1

2345

678

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

P

SCL CYCLE

NUMBER

S

A6

A5

A4

A3

A2

A1

A0

ACK

TX

NV

V

R3

R2

R1

R0

ACK

D7

D6

D5

D4

D3

D2

D1

D0

ACK

VREG

0

1

0

1

A2

A1

A0

0

0

0

0

1

0

0

0

1

D7

D6

D5

D4

D3

D2

D1

D0

NVREG

0

1

0

1

A2

A1

A0

0

0

0

1

0

0

0

0

1

D7

D6

D5

D4

D3

D2

D1

D0

NVREGxVREG

0

1

0

1

A2

A1

A0

0

0

1

1

0

0

0

0

1

XX

XX

XX

XX

VREGxNVREG

0

1

0

1

A2

A1

A0

0

0

1

0

1

0

0

0

1

XX

XX

XX

XX

Table 2. Command Byte Summary

Nonvolatile Memory

The internal EEPROM consists of an 8-bit nonvolatile

register that retains the value written to it before the

device is powered down. The nonvolatile register is

programmed with the midscale value at the factory.

Power-Up

Upon power-up, the MAX5417/MAX5418/MAX5419

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 MAX5417/MAX5418/MAX5419 feature a low-power

standby. When the device is not being programmed, it

goes into standby mode and power consumption is

typically 500nA.

Applications Information

The MAX5417/MAX5418/MAX5419 are intended for cir-

cuits requiring digitally controlled adjustable resis-

tance, such as LCD contrast control (where voltage

biasing adjusts the display contrast), or for programma-

ble filters with adjustable gain and/or cutoff frequency.

Positive LCD Bias Control

Figures 9 and 10 show an application where the volt-

age-divider or variable resistor is used to make an

adjustable, positive LCD bias voltage. The op amp pro-

vides buffering and gain to the resistor-divider network

made by the potentiometer (Figure 9) or to a fixed

resistor and a variable resistor (see Figure 10).

Programmable Filter

Figure 11 shows the configuration for a 1st-order pro-

grammable filter. The gain of the filter is adjusted by

R2, and the cutoff frequency is adjusted by R3. Use the

following equations to calculate the gain (G) and the

G

R

R

f

RC

C

=+

=

××

1

1

2

1

23

π

30V

5V

W

H

L

MAX5417

MAX5418

MAx5419

30V

5V

W

H

L

MAX5417

MAX5418

MAX5419

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

Figure 10. Positive LCD Bias Control Using a Variable Resistor

X = Don’t care.