32-Tap, Nonvolatile, Linear-Taper Digital

Potentiometers in SOT23

_______________________________________________________________________________________

7

Detailed Description

The MAX5471/MAX5472/MAX5474/MAX5475 contain a

resistor array with 31 resistive elements (Figures 2 and

3). The MAX5471/MAX5474 have a total end-to-end

resistance of 50k

Ω, and the MAX5472/MAX5475 have

an end-to-end resistance of 100k

Ω. The MAX5471/

MAX5472 wiper is connected to the high terminal, and

the low terminal is internally connected to ground, mak-

ing the device a variable resistor. The MAX5474/

MAX5475 allow access to the high, low, and wiper ter-

minals for a standard voltage-divider configuration.

The wiper is moved among the 32 tap points through a

simple 3-wire interface. Nonvolatile memory allows the

wiper position to be stored and recalled to the same

point upon power-up.

Digital Interface

Logic inputs CS, U/D, and INC control the wiper posi-

tion and store it in nonvolatile memory (see the Truth

Table). The chip-select (CS) input enables the serial

interface when low and disables the interface when

high. The position of the wiper is stored when CS transi-

tions from low to high and INC is high (see the Storing

Wiper Position section).

With the serial interface active (CS low), a high-to-low

(falling edge) transition on INC moves the wiper posi-

tion by one resistive element in the direction deter-

mined by the state of U/D. If U/D is high, the wiper

increments and it increases the resistance between W

and L (it decreases the resistance between H and W).

If U/D is low, the wiper decrements and it decreases

the resistance between W and L (it increases the resis-

tance between H and W). The direction of the wiper

(state of U/D) can be changed at any time as long as

the setup and hold times are met.

Since the MAX5471/MAX5472 have the wiper internally

connected to H, an increment command increases the

resistance between H and GND, and a decrement com-

mand decreases the resistance between H and GND.

The wiper performs a make-before-break transition,

ensuring that there is never an open circuit during a

transition from one resistor tap to another. When the

wiper is at either end of the resistor array (max/min),

additional transitions in the direction of the endpoint do

not change the counter value (the wiper does not wrap

around).

Storing Wiper Position

The position of the wiper is stored in nonvolatile memo-

ry whenever CS transitions low-to-high (rising edge)

while INC is high. Upon power-up, the wiper returns to

this stored position. By keeping INC low while taking

CS high, the serial interface can be disabled and the

potentiometer placed in standby without storing the lat-

est wiper position. The factory-default wiper position

is midscale.

These devices can also be operated like a one-time

programmable (OTP) device. Once the desired wiper

position is trimmed and stored in nonvolatile memory,

and INC to GND. The disabled interface places the

device in standby and disallows any changes to the

wiper position. In OTP mode, these devices become a

fixed 3-terminal potentiometer or a 1-terminal resistor to

GND with less than 1µA of supply current.

CS

INC

WIPER POSITION

STORED

WIPER POSITION

NOT STORED

U/D

Figure 1. Digital Interface and Timing Diagram