Circuit Note CN-0405 Devices Connected/Referenced Single-Channel, 64-Position, Push-Button, AD5116 8% Resistor Tolerance, Nonvolatile Circuits from the Lab reference designs are engineered and Digital Potentiometer tested for quick and easy system integration to help solve todays analog, mixed-signal, and RF design challenges. For more General-Purpose Comparator with ADCMP371 information and/or support, visit www.analog.com/CN0405. Push-Pull Output Stage 150 mA, Low Quiescent Current, ADP121 CMOS Linear Regulator High Voltage Output DAC with Push-Button Control The circuit allows a low voltage digital potentiometer to control EVALUATION AND DESIGN SUPPORT a high voltage source up to 20 V from batteries or other sources Circuit Evaluation Boards through simple push-button switches, offering ease of use and CN-0405 Circuit Evaluation Board (EVAL-CN0405-EB1Z) optimum power efficiency. The AD5116 digital potentiometer Design and Integration Files provides 64 wiper positions with an end-to-end resistor tolerance Schematics, Layout Files, Bill of Materials error of 8%, making it suitable for wide range of adjustment. CIRCUIT FUNCTION AND BENEFITS In addition, the AD5116 contains an EEPROM that can manually This circuit shown in Figure 1 provides a complete solution that save the wiper position to its desirable position through a push- replaces a classical high voltage mechanical potentiometer with button. This feature is useful in applications requiring a default a push-button controlled digital potentiometer. position on power-up. JP1 FILTER L1 R8 330nH 50 P1 V = 20V IN C10 330F P2 V OUT 3 C3 C4 C7 C8 Q2 1F 0.1F 1F 0.1F P3 2 1 R3 V R4 DD 1k 80.6k IN R1 1.15k Q1 ADCMP371 R5 13k IN+ V DD 4.67V 3.3V VIN VOUT MANUAL STORAGE R2 ADP121 C1 C2 C5 C6 PUSH-DOWN 100k 350 1F 0.1F 1F 0.1F GND V ASE DD EN NC A PU AD5116 PUSH-UP BUTTON W PD V DD B GND PUSH-DOWN BUTTON Figure 1. High Voltage DAC Circuit (Simplified Schematic. All Components, Connections, and Decoupling Not Shown) Rev. 0 Circuits from the Lab reference designs from Analog Devices have been designed and built by Analog Devices engineers. Standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperature. However, you are solely responsible for testing the circuit and One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. determining its suitability and applicability for your use and application. Accordingly, in no event shall Tel: 781.329.4700 www.analog.com Analog Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due Fax: 781.461.3113 2017 Analog Devices, Inc. All rights reserved. to any cause whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page) 15187-001CN-0405 Circuit Note As the DAC output voltage increases, Q2 must be closed for a CIRCUIT DESCRIPTION longer period of time therefore, the comparator output must be The circuit shown in Figure 1 is a simple, high voltage, variable high longer. Under these conditions, the comparator output is a output switching controller using the AD5116 64-position digital series of faster positive-going output pulses at a higher frequency. potentiometer in conjunction with ADCMP371 comparator that The reverse happens if the DAC output voltage is decreased. has a push-pull output stage and low power consumption suitable for battery-powered portable equipment. Negative feedback forces the average value of the comparator inputs to be equal for any increase or decrease in DAC output The circuit is powered entirely from the V source and accepts an IN voltage. input voltage up to 20 V. The voltage from the divider, R1 and R2, The filtered output voltage, V , is determined by the following is regulated to 3.3 V using the ADP121, a 30 A, low quiescent OUT equation: current, low dropout linear regulator. The regulated 3.3 V supplies the V voltage to the AD5116 digital potentiometer and the DD R4 V = V + (1) 1 ADCMP371 comparator. OUT W R5 Circuit Operation where V is the DAC output voltage at the wiper terminal, W. W The circuit is a switched mode power supply where the output The AD5116 digital potentiometer generates a divided voltage at voltage is regulated by controlling the switching frequency of wiper to Terminal B that is proportional to the V voltage. The DD the feedback network. resistance between Terminal A and Terminal B is nominally 5 k The output voltage, V , is controlled with a feedback OUT and is divided to 64 taps. At the lower end of the scale, the comparator that compares the R4 and R5 divided output voltage typical wiper resistance, RW, decreases to between 45 and 70 . to a reference voltage derived from the wiper of the AD5116 The output voltage at VW with respect to GND is digital potentiometer. The output of the comparator drives the R WB NMOS transistor, Q1, which in turn drives the series pass PMOS V = V (2) W A R AB transistor, Q2. The negative feedback causes Q2 to switch on and off to force the average voltage at the IN pin of the comparator D R = R + R (3) WB AB W to be equal to the voltage on the IN+ pin. There is only a small 64 amount of power dissipated in Q1 and Q2 because they are where: either on or off. R is the wiper resistance at bottom scale. WB When the Q1 transistor is on (saturation region), the voltage RAB is the end-to-end resistance. drop across it is minimal, and when it is off (cutoff region), VA is the voltage at the top of the divider string, equal to VDD. there is almost no current through the power path. The D is the decimal equivalent of the binary code in RDAC register. switching frequency depends on the AD5116 digital-to-analog The RDAC register is controlled using the PD and PU push- converter (DAC) output voltage. buttons. When a desirable wiper position is established, it can When the DAC output is low voltage, Q2 must be open most of ASE be stored to EEPROM memory through the push-button, the time therefore, the comparator output must be low most of which sets the default position upon power-up. the time. Under these conditions, the comparator output is a series of short positive-going pulses at a low frequency. Rev. 0 Page 2 of 6