Digital Interface

The MAX5128 features a 2-wire interface consisting of

two logic inputs (UP and DN). Logic inputs UP and DN

control the wiper position and program the position to

the nonvolatile memory. Transition UP from high to low

with DN low to increment the wiper position. Transition

DN from high to low with UP low to decrement the wiper

position (see Figures 1, 2, and 3). When the wiper decre-

ments, it decreases the resistance between W and L

(and it increases the resistance between H and W).

To program the nonvolatile memory, force UP high,

then force DN high, and then transition either input

(UP/DN) from high to low (see Figure 3).

The wiper performs a make-before-break transition,

ensuring that an open circuit during a transition from

one resistor tap to another does not occur. The wiper

does not wrap around when it reaches either end of the

resistor array (max/min). Additional transition com-

mands in the direction of the end point do not change

the tap position.

The logic inputs also feature pulse glitch immunity

(20ns) to protect the wiper from transitioning due to

glitches (see Figure 4).

Write NV Register

The internal EEPROM consists of a 7-bit nonvolatile

memory that retains the value written to it even after

power-down. To program the nonvolatile memory, force

UP high, then force DN high, and then transition either

input (UP/DN) from high to low. A nonvolatile write

requires a busy time of 14ms (max). During the busy

time, any nonvolatile write requests are ignored as well

as requests to increment or decrement the wiper posi-

tion. Upon power-up, the wiper returns to the position

stored in the nonvolatile register. The MAX5128 fea-

tures a factory-default wiper position of midscale.

128-Tap, Nonvolatile, Linear-Taper Digital

Potentiometer in 2mm x 2mm µDFN Package

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9

UP

DN

NVM

WRITE

UP

DN

WIPER

INCREMENTS

NVM

WRITE

WIPER

DECREMENTS

NVM

WRITE

WIPER

INCREMENTS

WIPER

DECREMENTS

Figure 3. Digital-Interface Command Diagram