Detailed Description

The MAX5450–MAX5455 contain two independent

resistor arrays each with 255-resistive elements. 256-

tap points are accessible to the wiper along the resistor

cuitry sets the wiper to midscale (position 127) at

power-up.

Logic inputs CS, U/D, and INC determine the wiper

position of the MAX5450–MAX5455. With CS low and

U/D high, a high-to-low (falling edge) transition on INC,

increments the internal counter, which increases the

resistance between W and L. When both CS and U/D

are low, a high-to-low INC transition decrements the

internal counter, decreasing the resistance between W

and L (Figure 1). The wiper performs a make-before-

break transition ensuring that there is never an open

circuit during a transition from one resistor tap to anoth-

er. When the wiper is at either end (max/min) of the

resistor array, additional transitions in the direction of

the endpoint will not change the counter value (the

counter will not wrap around).

The MAX5450/MAX5452/MAX5454 are similar to the

MAX5451/MAX5453/MAX5455 except for internal con-

nections. The MAX5450/MAX5452/MAX5454 internally

connect INC1 to INC2, U/D1 to U/D2, W1 to H1, and

W2 to H2 (Figures 3 and 4). The internal connections

configure the MAX5450/MAX5452/MAX5454 to be vari-

able resistors.

Applications Information

The MAX5450–MAX5455 are ideal for adjustable volt-

age or adjustable gain circuits where accurate

adjustable resistances are required.

Adjustable Current to Voltage Converter

Figure 5 shows the MAX5450/MAX5452/MAX5454 with

a MAX4250 low-noise op amp to fine-tune a current to

voltage converter. The physical sizes of both devices

minimize circuit space.

Adjustable Gain Amplifier

Figures 6a and 6b shows the MAX5450–MAX5455 digi-

tally adjusting the gain of the MAX4493 general-pur-

pose, dual supply op amp. Figure 6a shows the

MAX5450/MAX5452/MAX5454 variable resistor in

series with a resistor to ground to form the adjustable

gain control. Figure 6b shows the MAX5451/MAX5453/

MAX5455 as a 3-terminal potentiometer. In these appli-

cations the low 5ppm/°C ratiometric tempco allows for

a very stable adjustable gain over temperature.

Adjustable Linear Regulator

In Figure 7, the MAX5450/MAX5452/MAX5454 is shown

digitally adjusting the output voltage of the MAX8866

dual linear regulator. In this circuit, the MAX5450/

MAX5452/MAX5454 is connected in series with a resis-

tor to ground to form the adjustable feedback stage.

The 8-bit MAX5450/MAX5452/MAX5454 allows precise

tuning of the output voltage.

Dual, 256-Tap, Up/Down Interface,

Digital Potentiometers

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Figure 1. Digital Interface and Timing diagram

CS_