CAT5126

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5

Detailed Description

The CAT5126 devices are 10 k

W/50 kW/100 kW

(end-to-end resistance) digitally controlled potentiometers.

They have 32-tap positions that are accessible to the wiper

potentiometers have an optional one-time programmable

interface can then be disabled, permanently preventing

unwanted adjustment.

Digital Interface Operation

The CAT5126 devices have two modes of operation when

the serial interface is active: increment mode and decrement

mode. The serial interface is only active when CS is low.

The CS and U/D inputs control the position of the wiper

along the resistor array. When CS transitions from high to

low, the part goes into increment mode if U/D is high

(Figure 6), and into decrement mode if U/D is low

(Figure 7). Once the mode is set, the device remains in that

mode until CS goes high. A low-to-high transition at the U/D

increments or decrements the wiper position depending on

the current mode.

The value of the counter is then stored and the wiper

position is maintained till the device is Powered down.

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 (max/min) of the resistor array, additional

transitions in the direction of the endpoint do not change the

counter value (the counter does not wrap around).

One−Time Programming

The factory-set default position of the wiper on power-up

is tap 16. However, the power-up position can be changed

once using the one-time programming feature. After the

wiper is moved to the desired position, the programming

sequence is initiated by setting U/D high, applying 10 V to

voltage should then be taken to zero. After the device is

The wiper position is still adjustable, but always returns to

this programmed position on power−up.

Figure 6. Increment Mode Serial Interface Timing Diagram

CS

U/D

Figure 7. Decrement Mode Serial Interface Timing Diagram

U/D

CS