CAT5128 32tap Digital Up/Down Control Potentiometer (POT) Description The CAT5128 is a single digital POT designed as an electronic replacement for mechanical potentiometers and trim pots. Ideal for CAT5128 Functional Diagrams V CC A A A 5 BIT 31 UP UP/DOWN COUNTER 30 UP/DOWN Control W 29 V CC Power On DOWN 28 Recall W B TRANS FER GND GATES UP 2 DOWN 1 GND 0 B B W Figure 1. General Figure 2. Detailed Figure 3. Electronic Potentiometer Implementation Pin Description Device Operation The CAT5128 operates like a digitally controlled UP: Step-Up Control Input potentiometer with A and B equivalent to the high and low When DOWN input is high, a high-to-low transition on terminals and W equivalent to the mechanical UP input will cause the wiper to move one increment toward potentiometers wiper. There are 32 available tap positions the A terminal. including the resistor end points, A and B. There are 31 DOWN: Step-Down Control Input resistor elements connected in series between the A and B A high-to-low transition on DOWN input will cause the terminals. The wiper terminal is connected to one of the 32 wiper to move one increment towards the B terminal. taps and controlled by two inputs, UP and DOWN. These A: High End Potentiometer Terminal inputs control a five-bit up/down counter whose output is A is the high end terminal of the potentiometer. It is not decoded to select the wiper position. required that this terminal be connected to a potential greater A high-to-low transition on DOWN input will decrement than the B terminal. Voltage applied to the A terminal cannot one step the wiper position (R will decrease with 1LSB WB exceed the supply voltage, V or go below ground, GND. CC and R will increase with 1LSB). If and only if DOWN WA W: Wiper Potentiometer Terminal input is high, a high-to-low transition on UP input will W is the wiper terminal of the potentiometer. Its position increment one step the wiper position (R will increase WB on the resistor array is controlled by the control inputs, UP with 1LSB and R will decrease with 1LSB). WA and DOWN. Voltage applied to the W terminal cannot The wiper, when at either fixed terminal, acts like its exceed the supply voltage, V or go below ground, GND. mechanical equivalent and does not move beyond the last CC position. When the CAT5128 is powered-down, the wiper B: Low End Potentiometer Terminal position is reset. When power is restored, the counter is set B is the low end terminal of the potentiometer. It is not to the mid point, tap 15. required that this terminal be connected to a potential less than the A terminal. Voltage applied to the B terminal cannot exceed the supply voltage, V or go below ground, GND. CC B and A are electrically interchangeable.