AN-1150 APPLICATION NOTE One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com Controlling the AD5111/AD5113/AD5115 Using a Traditional Dial Interface by Miguel Usach INTRODUCTION The operation of the digital up/down interface is simple: when the CS pin is pulled low, the part reads the status of the U/D pin, incrementing or decrementing an internal counter at each CLK falling edge, as shown in Figure 2. Digital potentiometers are available in a variety of interfaces, both digital and manual. The manual, or push-button, interface is controlled directly by adding two push-button switches, such as the AD5116 or the AD5228. Press the up button to increase the resistance, and push the down button to decrease the resistance, as shown in Figure 1. CS CLK U/D VDD RWB PUSH-UP BUTTON Figure 2. Up/Down Interface Operation PU The AD5111/AD5113/AD5115 digital potentiometers offer guaranteed low resistor tolerance errors of ±8% and up to ±6 mA current density, making them ideal choices for a mechanical potentiometer replacement. ADAPTIVE DEBOUNCER Figure 1. AD5228 Push-Button Interface The low current consumption (750 nA typical) and 2.3 V operation increase the battery life, and the small package (2 mm × 2 mm LFCSP) makes the AD5111/AD5113/AD5115 ideal for portable applications. The push-button interface includes an internal button debouncer to filter the voltage glitches, as well as internal resistors, making this interface suitable for a large number of switches. If the application requires another type of manual controller, such as a rotary dial, the push-button interface is not suitable. In such cases, a digital up/down interface can be used. This interface is designed to increase or decrease the linear resistance at high rates of speed, with a clock up to 50 MHz. The digital up/down interface typically provides three input pins, as follows: • • • The CS pin enables the part. The U/D pin selects increment or decrement. The CLK pin is the clock input. ROTARY DIAL The rotary dial or knob is a common mechanical potentiometer controller. This type of controller can be emulated by using a mechanical encoder. The mechanical rotary encoder typically provides three pins: one for ground (common) and two additional output pins for generating square signals with a constant out-of-phase between them, as shown in Figure 3. CCW CW CHANNEL A 10569-003 PUSH-DOWN BUTTON 10569-001 PD 10569-002 The digital potentiometer offers an optimal replacement for a mechanical potentiometer due to its small package, better reliability, and high accuracy with smaller voltage glitches. CHANNEL B Figure 3. Mechanical Encoder Pulses Rev. 0 | Page 1 of 2 AN-1150 Application Note CONNECTION WITH THE DIGIPOT HYBRID INTERFACE The mechanical encoder does not pull the output pin high, but, instead, places the pin at high impedance. The signal pins require external pull-up resistors. In addition, the interface allows hybrid control between manual and digital operation. The hybrid interface allows the use of the extra functionality implemented in the part, such as the EEPROM or shutdown mode. The AD5111/AD5113/AD5115 offer extra features such as shutdown and EEPROM memory. To ensure that these commands are not executed, the U/D pin can be updated only when CLK is low. The hybrid interface can be implemented by adding an external multiplexer between the mechanical encoder and the microcontroller. Four GPIO pins are required for this interface: one to select the controller and three additional pins to drive the CS, U/D, and CLK pins. The CS pin is required to disable the part, ensuring a controlled environment when the multiplexer switches between lines. By including a fast D-type flip-flop, as shown in Figure 4, the U/D pin can be updated without concern for the CLK level. The only requirement is that the propagation delay in the D-type flip-flop must be <10 ns. MECHANICAL ENCODER AD5111/AD5113/AD5115 VDD VDD VDD R R CHANNEL A U/D Q D D-TYPE CLK FLIP-FLOP CHANNEL B UP/DOWN CONTROL LOGIC CS EN 10569-004 CLK Figure 4. Circuit Diagram Connection MECHANICAL ENCODER ADG636 VDD VDD R CHANNEL A CHANNEL B AD5111/AD5113/AD5115 VDD VDD R Q D D-TYPE CLK FLIP-FLOP S1A D1 S1B U/D UP/DOWN CONTROL LOGIC CS S2A EN D2 CLK S2B GPIO0 GPIO1 A0 GPIO2 A1 GPIO3 LOGIC VDD EN Figure 5. Hybrid Interface Connection ©2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. AN10569-0-3/12(0) Rev. 0 | Page 2 of 2 10569-005 MICROCONTROLLER