64-Position Up/Down Control Digital Potentiometer AD5227 FEATURES FUNCTIONAL BLOCK DIAGRAM 64-position digital potentiometer 10 kΩ, 50 kΩ, 100 kΩ end-to-end terminal resistance Simple up/down digital or manual configurable control Midscale preset Low potentiometer mode tempco = 10 ppm/°C Low rheostat mode tempco = 35 ppm/°C Ultralow power, IDD = 0.4 µA typ and 3 µA max Fast adjustment time, ts = 1 µs Chip select enable multiple device operation Low operating voltage, 2.7 V to 5.5 V Automotive temperature range, −40°C to +105°C Compact thin SOT-23-8 (2.9 mm × 3 mm) Pb-free package VDD AD5227 A CS 6-BIT UP/DOWN CONTROL LOGIC U/D CLK W B POR MIDSCALE WIPER REGISTER 04419-0-001 GND Figure 1. APPLICATIONS Mechanical potentiometer and trimmer replacements LCD backlight, contrast, and brightness controls Portable electronics level adjustment Programmable power supply Digital trimmer replacements Automatic closed-loop control GENERAL DESCRIPTION The AD5227 is Analog Devices’ latest 64-step up/down control digital potentiometer1. This device performs the same electronic adjustment function as a 5 V potentiometer or variable resistor. Its simple 3-wire up/down interface allows manual switching or high speed digital control. The AD5227 presets to midscale at power-up. When CS is enabled, the devices changes step at every clock pulse. The direction is determined by the state of the U/D pin (see Table 1). The interface is simple to activate by any host controller, discrete logic, or manually with a rotary encoder or pushbuttons. The AD5227’s 64-step resolution, small footprint, and simple interface enable it to replace mechanical potentiometers and trimmers with typically 6× improved resolution, solid-state reliability, and design layout flexibility, resulting in a considerable cost savings in end users’ systems. 1 The AD5227 is available in a compact thin SOT-23-8 (TSOT-8) Pb-free package. The part is guaranteed to operate over the automotive temperature range of −40°C to +105°C. Users who consider EEMEM potentiometers should refer to some recommendations in the Applications section. Table 1. Truth Table CS 0 0 1 1 CLK ↓ ↓ X U/D 0 1 X Operation1 RWB Decrement RWB Increment No Operation RWA increments if RWB decrements and vice versa. The terms digital potentiometer and RDAC are used interchangeably. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved. AD5227 TABLE OF CONTENTS Electrical Characteristics ................................................................. 3 Layout and Power Supply Biasing ............................................ 11 Interface Timing Diagrams ......................................................... 4 Applications..................................................................................... 12 Absolute Maximum Ratings............................................................ 5 Manual Control with Toggle and Pushbutton Switches........ 12 ESD Caution.................................................................................. 5 Manual Control with Rotary Encoder..................................... 12 Pin Configuration and Function Descriptions............................. 6 Adjustable LED Driver .............................................................. 12 Typical Performance Characteristics ............................................. 7 Adjustable Current Source for LED Driver ............................ 12 Theory of Operation ...................................................................... 10 Automatic LCD Panel Backlight Control................................ 13 Programming the Digital Potentiometers............................... 10 6-Bit Controller .......................................................................... 13 Digital Interface .......................................................................... 11 Constant Bias with Supply to Retain Resistance Setting...... 14 Terminal Voltage Operation Range.......................................... 11 Outline Dimensions ....................................................................... 15 Power-Up and Power-Down Sequences.................................. 11 Ordering Guide .......................................................................... 15 REVISION HISTORY Revision 0: Initial Version Rev. 0 | Page 2 of 16 AD5227 ELECTRICAL CHARACTERISTICS 10 kΩ, 50 kΩ, 100 kΩ versions: VDD = 3 V ± 10% or 5 V ± 10%, VA = VDD, VB = 0 V, −40°C < TA < +105°C, unless otherwise noted. Table 2. Parameter DC CHARACTERISTICS RHEOSTAT MODE Resistor Differential Nonlinearity2 Resistor Integral Nonlinearity2 Nominal Resistor Tolerance3 Resistance Temperature Coefficient Wiper Resistance Symbol Conditions Min Typ1 Max Unit R-DNL R-INL ∆RAB/RAB (∆RAB/RAB)/∆T × 106 RW RWB, A = no connect RWB, A = no connect −0.5 −1 −20 ±0.15 ±0.3 +0.5 +1 +20 LSB LSB % ppm/°C Ω Ω DC CHARACTERISTICS POTENTIOMETER DIVIDER MODE Resolution N Integral Nonlinearity3 INL Differential Nonlinearity3, 4 DNL Voltage Divider Temperature Coefficient (∆VW/VW)/∆T × 106 Full-Scale Error VWFSE Zero-Scale Error VWZSE RESISTOR TERMINALS Voltage Range5 VA, B, W Capacitance A, B6 CA, B Capacitance W6 Common-Mode Leakage DIGITAL INPUTS (CS, CLK, U/D) Input Logic High Input Logic Low Input Current Input Capacitance6 POWER SUPPLIES Power Supply Range Supply Current Power Dissipation7 Power Supply Sensitivity DYNAMIC CHARACTERISTICS6, 8, 9 Bandwidth –3 dB CW ICM VIH VIL II CI VDD IDD PDISS PSSR Total Harmonic Distortion BW_10 k BW_50 k BW_100 k THD Adjustment Settling Time tS Resistor Noise Voltage eN_WB 35 100 50 VDD = 2.7 V VDD = 5.5 V −1 −0.5 Midscale ≥+31 steps from midscale ≤−32 steps from midscale With respect to GND f = 1 MHz, measured to GND f = 1 MHz, measured to GND VA = VB = VW −1 0 ±0.1 ±0.1 5 −0.5 0.5 0 200 6 +1 +0.5 0 +1 VDD Bits LSB LSB ppm/°C LSB LSB 140 V pF 150 pF 1 nA 2.4 0 VIN = 0 V or 5 V 5.5 0.8 ±1 V V µA pF 5.5 3 V µA 17 µW 0.05 %/% 5 2.7 VIH = 5 V or VIL = 0 V, VDD = 5 V VIH = 5 V or VIL = 0 V, VDD = 5 V VDD = 5 V ± 10% 0.4 RAB = 10 kΩ, midscale RAB = 50 kΩ, midscale RAB = 100 kΩ, midscale VA = 1 V rms, RAB = 10 kΩ, VB = 0 V dc, f = 1 kHz VA = 5 V ± 1 LSB error band, VB = 0, measured at VW RWB = 5 kΩ, f = 1 kHz 460 100 50 0.05 kHz kHz kHz % 1 µs 14 nV/√Hz Footnotes on the next page. Rev. 0 | Page 3 of 16 0.01 AD5227 Parameter Symbol INTERFACE TIMING CHARACTERISTICS (applies to all parts6, 10) Clock Frequency fCLK Input Clock Pulse Width tCH, tCL tCSS CS to CLK Setup Time tCSH CS Rise to CLK Hold Time tUDS U/D to Clock Fall Setup Time Conditions Min Clock level high or low 10 10 10 10 Typ1 Max 50 1 Unit MHz ns ns ns ns Typicals represent average readings at 25°C, VDD = 5 V. Resistor position nonlinearity error, R-INL, is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. 3 NL and DNL are measured at VW with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. VA = VDD and VB = 0 V. 4 DNL specification limits of ±1 LSB maximum are guaranteed monotonic operating conditions. 5 Resistor Terminals A, B, W have no limitations on polarity with respect to each other. 6 Guaranteed by design and not subject to production test. 7 PDISS is calculated from (IDD × VDD). CMOS logic level inputs result in minimum power dissipation. 8 Bandwidth, noise, and settling time are dependent on the terminal resistance value chosen. The lowest R value results in the fastest settling time and highest bandwidth. The highest R value results in the minimum overall power consumption. 9 All dynamic characteristics use VDD = V. 10 All input control voltages are specified with tR = tF = 1 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. Switching characteristics are measured using VDD = 5 V. 2 INTERFACE TIMING DIAGRAMS CS = LOW U/D = HIGH 04419-0-004 CLK RWB Figure 2. Increment RWB CS = LOW U/D = 0 CLK 04419-0-005 RWB Figure 3. Decrement RWB 1 CS 0 tCSS tCH tCSH tCL 1 CLK 0 tUDS 1 U/D 0 04419-0-006 tS RWB Figure 4. Detailed Timing Diagram(Only RWB Decrement Shown) Rev. 0 | Page 4 of 16 AD5227 ABSOLUTE MAXIMUM RATINGS Table 3. Parameter VDD to GND VA, VB, VW to GND Digital Input Voltage to GND (CS, CLK, U/D) Maximum Current IWB, IWA Pulsed IWB Continuous (RWB ≤ 5 kΩ, A open)1 IWA Continuous (RWA ≤ 5 kΩ, B open)1 IAB Continuous (RAB = 10 kΩ/50 kΩ/100 kΩ)1 Operating Temperature Range Maximum Junction Temperature (TJmax) Storage Temperature Lead Temperature (Soldering, 10 s – 30 s) Thermal Resistance2 θJA Rating −0.3 V, +7 V 0 V, VDD 0 V, VDD ±20 mA ±1 mA ±1 mA ±500 µA/ ±100 µA/±50 µA −40°C to +105°C 150°C −65°C to +150°C 245°C 230°C/W Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 1 Maximum terminal current is bounded by the maximum applied voltage across any two of the A, B, and W terminals at a given resistance, the maximum current handling of the switches, and the maximum power dissipation of the package. VDD = 5 V. 2 Package power dissipation = (TJmax – TA) / θJA. ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. 0 | Page 5 of 16 AD5227 CLK 1 U/D 2 AD5227 TOP VIEW A 3 (Not to Scale) GND 4 8 VDD 7 CS 6 B 5 W 04419-0-003 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 5. SOT-23-8 Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 Mnemonic CLK 2 3 4 5 6 7 8 U/D A GND W B CS VDD Description Clock Input. Each clock pulse executes the step-up or step-down of the resistance. The direction is determined by the state of the U/D pin. CLK is a negative-edge trigger. Logic high signal can be higher than VDD, but lower than 5.5 V. Up/Down Selections. Logic 1 selects up and Logic 0 selects down. U can be higher than VDD, but lower than 5.5 V. Resistor Terminal A. GND ≤ VA ≤ VDD. Common Ground. Wiper Terminal W. GND ≤ VW ≤ VDD. Resistor Terminal B. GND ≤ VB ≤ VDD. Chip Select. Active Low. Logic high signal can be higher than VDD, but lower than 5.5 V. Positive Power Supply, 2.7 V to 5.5 V. Rev. 0 | Page 6 of 16 AD5227 TYPICAL PERFORMANCE CHARACTERISTICS 0.25 0.25 –40°C +25°C +85°C +105°C VDD = 5.5V 0.05 0 –0.05 –0.10 –0.15 –0.20 0 8 16 24 32 40 CODE (Decimal) 48 56 0.10 0.05 0 –0.05 –0.10 –0.15 –0.20 –0.25 64 0 Figure 6. R-INL vs. Code vs. Temperature, VDD = 5 V 48 56 64 –0.1 –0.2 0.10 –0.3 FSE (LSB) 0.05 0 –0.05 –0.4 VDD = 5.5V –0.5 –0.6 –0.10 VDD = 2.7V –0.15 0 8 16 24 32 40 CODE (Decimal) 48 56 04419-0-013 –0.7 04419-0-008 RHEOSTAT MODE DNL (LSB) 0.15 –0.20 –0.8 –0.9 –40 64 Figure 7. R-DNL vs. Code vs. Temperature, VDD = 5 V –20 0 20 40 60 TEMPERATURE (°C) 80 100 Figure 10. Full-Scale Error vs. Temperature 0.25 1.0 –40°C +25°C +85°C +105°C VDD = 5.5V 0.20 0.15 0.9 0.8 VDD = 2.7V 0.7 0.05 0.6 ZSE (LSB) 0.10 0 –0.05 0.5 0.3 –0.15 0.2 –0.20 0 8 16 24 32 40 CODE (Decimal) 48 56 VDD = 5.5V 0.4 –0.10 04419-0-010 POTENTIOMETER MODE INL (LSB) 24 32 40 CODE (Decimal) 0 –40°C +25°C +85°C +105°C VDD = 5.5V 0.20 –0.25 16 Figure 9. DNL vs. Code vs. Temperature, VDD = 5 V 0.25 –0.25 8 04419-0-014 –0.25 0.15 04419-0-012 0.10 04419-0-007 RHEOSTAT MODE INL (LSB) 0.15 –40°C +25°C +85°C +105°C VDD = 5.5V 0.20 POTENTIOMETER MODE DNL (LSB) 0.20 0.1 0 –40 64 Figure 8. INL vs. Code, VDD = 5 V –20 0 20 40 60 TEMPERATURE (°C) 80 Figure 11. Zero-Scale Error vs. Temperature Rev. 0 | Page 7 of 16 100 AD5227 20 1 10kΩ 50kΩ 100kΩ VDD = 5.5V –20 0 20 40 60 TEMPERATURE (°C) 80 10 5 0 –5 –10 –15 –20 100 0 8 16 24 32 40 CODE (Decimal) 48 20 VDD = 5.5V NOMINAL RESISTANCE, RAB (kΩ) RAB = 100kΩ 04419-0-016 RAB = 50kΩ RAB = 10kΩ 0 20 40 60 TEMPERATURE (°C) 80 POTENTIOMETER MODE TEMPCO (ppm/°C) 1 –20 64 10kΩ 50kΩ 100kΩ VDD = 5.5V 15 10 5 0 –5 –10 –15 –20 100 0 8 16 24 32 40 CODE (Decimal) 48 56 64 Figure 16. Potentiometer Mode Tempco ∆RWB/∆T vs. Code Figure 13. Nominal Resistance vs. Temperature 120 6 REF LEVEL 0dB /DIV 6.0dB MARKER 461 441.868Hz MAG (A/R) –8.957dB TA = 25°C VDD = 5.5V VA = 50mV rms VDD = 2.7V 0 100 32 STEPS –6 16 STEPS 80 –12 8 STEPS –18 60 dB 4 STEPS VDD = 5.5V –24 2 STEPS –30 40 1 STEP –36 0 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 –42 04419-0-042 20 04419-0-017 WIPER RESISTANCE, RW (Ω) 56 Figure 15. Rheostat Mode Tempco ∆RWB/∆T vs. Code Figure 12. Supply Current vs. Temperature 0.1 –40 04419-0-018 RHEOSTAT MODE TEMPCO (ppm/°C) 15 04419-0-019 0.1 –40 04419-0-015 SUPPLY CURRENT (µA) VDD = 5.5V –48 100 –54 1k START 1 000.000Hz 10k 1M 100k STOP 1 000 000.000Hz Figure 14. Wiper Resistance vs. Temperature Figure 17. Gain vs. Frequency vs. Code, RAB = 10 kΩ Rev. 0 | Page 8 of 16 AD5227 REF LEVEL 0dB /DIV 6.0dB MARKER 100 885.289Hz MAG (A/R) –9.060dB TA = 25°C VDD = 5.5V VA = 50mV rms 0 32 STEPS –6 150 16 STEPS –12 IDD (µA) 8 STEPS –18 dB 200 4 STEPS –24 100 2 STEPS VDD = 5V –30 1 STEP 50 –36 04419-0-024 6 04419-0-043 –42 –48 –54 1k 10k 100k 1M FREQUENCY (Hz) 1M 100k START 1 000.000Hz VDD = 3V 0 10k STOP 1 000 000.000Hz Figure 18. Gain vs. Frequency vs. Code, RAB = 50 kΩ REF LEVEL 0dB /DIV 6.0dB MARKER 52 246.435Hz MAG (A/R) –9.139dB 32 STEPS –6 1.2 TA = 25°C VDD = 5.5V VA = 50mV rms 0 8 STEPS –18 A = OPEN TA = 25°C 1.0 16 STEPS –12 4 STEPS –24 2 STEPS –30 1 STEP –36 RAB = 10kΩ 0.8 0.6 0.4 RAB = 50kΩ 0.2 –42 RAB = 100kΩ 04419-0-044 –48 –54 1k 10k START 1 000.000Hz 0 0 8 16 1M 100k 04419-0-025 dB Figure 21. IDD vs. CLK Frequency THEORETICAL IWB_MAX (mA) 6 10M 24 32 40 CODE (Decimal) 48 56 64 STOP 1 000 000.000Hz Figure 19. Gain vs. Frequency vs. Code, RAB = 100 kΩ Figure 22. Maximum IWB vs. Code 0 VB = 0V STEP = MIDSCALE, VA = VDD, VB = 0V VA 1 PSRR (dB) –20 STEP N+1 VW STEP N VDD = 3V DC ±10% p-p AC –40 VDD = 5V VA = 5V VB = 0V –60 100 1k 10k FREQUENCY (Hz) 100k 04419-0-023 VDD = 5V DC ±10% p-p AC 04419-0-022 2 CH1 2.00V 1M CH2 50.0mV M 400ns A CH2 T 0.00000s Figure 23. Step Change Settling Time Figure 20. PSRR Rev. 0 | Page 9 of 16 60.0mV AD5227 THEORY OF OPERATION The AD5227 is a 64-position 3-terminal digitally controlled potentiometer device. It presets to a midscale at system poweron. When CS is enabled, changing the resistance settings is achieved by clocking the CLK pin. It is negative-edge triggered, and the direction of stepping is determined by the state of the U/D input. When the wiper reaches the maximum or the minimum setting, additional CLK pulses do not change the wiper setting. The end-to-end resistance, RAB, has 64 contact points accessed by the wiper terminal, plus the B terminal contact, assuming that RWB is used (see Figure 25). Clocking the CLK input steps, RWB by one step. The direction is determined by the state of U/D pin. The change of RWB can be determined by the number of clock pulses, provided that the AD5227 has not reached its maximum or minimum scale. ∆RWB can, therefore, be approximated as VDD R ⎛ ⎞ ∆RWB = ±⎜ CP × AB + RW ⎟ 64 ⎝ ⎠ AD5227 6-BIT UP/DOWN CONTROL LOGIC CLK A where: W CP is the number of clock pulses. RAB is the end-to-end resistance. RW is the wiper resistance contributed by the on-resistance of the internal switch. B GND WIPER REGISTER 04419-0-026 POR MIDSCALE Since in the lowest end of the resistor string a finite wiper resistance is present, care should be taken to limit the current flow between W and B in this state to a maximum pulse current of no more than 20 mA. Otherwise, degradation or possible destruction of the internal switches can occur. Figure 24. Functional Block Diagram A RS RS RS W RW RDAC UP/DOWN CTRL AND DECODE R ∆RWA = ±⎛⎜ (64 − CP ) AB + RW ⎞⎟ 64 ⎝ ⎠ RS B RS = RAB/64 04419-0-027 D0 D1 D2 D3 D4 D5 Similar to the mechanical potentiometer, the resistance of the RDAC between the Wiper W and Terminal A also produces a digitally controlled complementary resistance, RWA. When these terminals are used, the B terminal can be opened or shorted to W. Similarly, ∆RWA can be approximated as Equations 1 and 2 do not apply when CP = 0. Figure 25. AD5227 Equivalent RDAC Circuit PROGRAMMING THE DIGITAL POTENTIOMETERS Rheostat Operation If only the W-to-B or W-to-A terminals are used as variable resistors, the unused terminal can be opened or shorted with W. This operation is called rheostat mode and is shown in Figure 26. A W B Potentiometer Mode Operation If all three terminals are used, the operation is called potentiometer mode. The most common configuration is the voltage divider operation as shown in Figure 27. A W B The typical distribution of the resistance tolerance from device to device is process lot dependent. It is possible to have ±20% tolerance. W B VI 04419-0-028 A (2) A VC W Figure 26. Rheostat Mode Configuration B 04419-0-029 CS U/D (1) Figure 27. Potentiometer Mode Configuration Rev. 0 | Page 10 of 16 AD5227 ∆VWB = + CP V A U/D = 1 64 (3) ∆VWB = − CP V A U/D = 0 64 (4) Unlike rheostat mode operation where the absolute tolerance is high, potentiometer mode operation yields an almost ratiometric function of CP/64 with a relatively small error contributed by the RW term. The tolerance effect is, therefore, almost canceled. Although the thin film step resistor, RS, and CMOS switches resistance, RW, have very different temperature coefficients, the ratiometric adjustment also reduces the overall temperature coefficient to 5 ppm/°C except at low value codes where RW dominates. TERMINAL VOLTAGE OPERATION RANGE The AD5227 is designed with internal ESD protection diodes (Figure 29), but the diodes also set the boundary of the terminal operating voltages. Voltage present on Terminal A, B, or W that exceeds VDD by more than 0.5 V is clamped by the diode and, therefore, elevates VDD. There is no polarity constraint between VAB, VWA, and VWB, but they cannot be higher than VDD-to-GND. POWER-UP AND POWER-DOWN SEQUENCES Because of the ESD protection diodes, it is important to power on VDD before applying any voltage to Terminals A, B, and W. Otherwise, the diodes are forward-biased such that VDD can be powered unintentionally and can affect the rest of the system circuit. Similarly, VDD should be powered down last. The ideal power-on sequence is in the following order: GND, VDD, VA/B/W, and digital inputs. VDD A W Potentiometer mode operation includes an op amp gain configuration among others. The A, W, and B terminals can be input or output terminals and have no polarity constraint provided that |VAB|, |VWA|, and |VWB| do not exceed VDD-to-GND. B GND 04419-0-031 The change of VWB is known provided that the AD5227 has not reached the maximum or minimum scale. If one ignores the effect of the wiper resistance, the transfer functions can be simplified as Figure 29. Maximum Terminal Voltages Set by VDD and GND DIGITAL INTERFACE LAYOUT AND POWER SUPPLY BIASING The AD5227 contains a 3-wire serial input interface. The three inputs are clock (CLK), chip select (CS), and up/down control (U/D). These inputs can be controlled digitally for optimum speed and flexibility It is a good practice to use compact, minimum lead length layout design. The leads to the input should be as direct as possible with a minimum conductor length. Ground paths should have low resistance and low inductance. It is also good practice to bypass the power supplies with quality capacitors. Low ESR (equivalent series resistance) 1 µF to 10 µF tantalum or electrolytic capacitors should be applied at the supplies to minimize any transient disturbance and filter low frequency ripple. When CS is pulled low, a clock pulse increments or decrements the up/down counter. The direction is determined by the state of the U/D pin. When a specific state of the U/D remains, the device continues to change in the same direction under consecutive clocks until it comes to the end of the resistance setting. All digital inputs, CS, CLK, and U/D pins, are protected with a series input resistor and a parallel Zener ESD structure as shown in Figure 28. LOGIC AD5227 04419-0-030 1kΩ Figure 30 illustrates the basic supply bypassing configuration for the AD5227. The ground pin of the AD5227 is a digital ground reference that should be joined to the common ground at a single point to minimize the digital ground bounce. VDD Figure 28. Equivalent ESD Protection Digital Pins + C2 10µF C1 0.1µF VDD 04419-0-032 GND Figure 30. Power Supply Bypassing Rev. 0 | Page 11 of 16 AD5227 APPLICATIONS MANUAL CONTROL WITH TOGGLE AND PUSHBUTTON SWITCHES ADJUSTABLE LED DRIVER The AD5227’s simple interface allows it to be used with mechanical switches for simple manual operation. The states of the CS and U/D can be selected by toggle switches and the CLK input can be controlled by a pushbutton switch. Because of the numerous bounces due to contact closure, the pushbutton switch should be debounced by flip-flops or by the ADM812 as shown in Figure 31. The AD5227 can be used in many electronics-level adjustments such as LED drivers for LCD panel backlight control. Figure 33 shows an adjustable LED driver. The AD5227 sets the voltage across the white LED D1 for the brightness control. Since U2 handles up to 250 mA, a typical white LED with VF of 3.5 V requires a resistor, R1, to limit the U2 current. This circuit is simple but not power-efficient, therefore the U2 shutdown pin can be toggled with a PWM signal to conserve power. 5V AD5227 5V CS C1 1µF U/D C2 0.1µF VCC VDD CLK RESET 04419-0-033 MR INCREMENT ADM812 GND V+ U1 AD5227 A CS CLK U/D – U2 AD8591 R1 SD 6Ω W + 10kΩ WHITE LED D1 V– B GND Figure 31. Manual Push Button Up/Down Control 04419-0-035 UP/DOWN C3 0.1µF PWM MANUAL CONTROL WITH ROTARY ENCODER Figure 32 shows another way of using AD5227 to emulate mechanical potentiometer in a rotary knob operation. The rotary encoder U1 has a C ground terminal and two out-ofphase signals, A and B. When U1 is turned clockwise, a pulse generated from the B terminal leads a pulse generated from the A terminal and vice versa. Signals A and B of U1 pass through a quadrature decoder U2 that translates the phase difference between A and B of U1 into compatible inputs for U3 AD5227. Therefore, when B leads A (clockwise), U2 provides the AD5227 with a logic high U/D signal, and vice versa. U2 also filters noise, jitter, and other transients as well as debouncing the contact bounces generated by U1. Figure 33. Low Cost Adjustable LED Driver ADJUSTABLE CURRENT SOURCE FOR LED DRIVER Since LED brightness is a function of current rather than forward voltage, an adjustable current source is preferred over a voltage source as shown in Figure 34. VIN 5V VOUT ARM-1.5 5V SD GND W CLK PWM B U/D 10kΩ A RSET 0.1Ω R1 418kΩ QUADRATURE DECODER R2 10kΩ U3 2 3 4 LS7084 RBIAS CLK VDD U/D VSS X4/X1 A 5V DIGITAL POTENTIOMETER A1 U2 B C A VDD CS GND R3 10kΩ 1 U1 ROTARY ENCODER AD5227 ADP3333 5V R1 10kΩ U2 U1 B AD5227 8 1 7 2 6 3 A1 5 4 CLK VDD U/D CS GND V+ U3 7 AD8591 B1 6 W1 5 V– B1 + VL D1 ID W1 04419-0-034 RE11CT-V1Y12-EF2CS Figure 32. Manual Rotary Control – 8 04419-0-036 5V Figure 34. Adjustable Current Source for LED Driver The load current can be found as the VWB of the AD5227 divided by RSET. ID = Rev. 0 | Page 12 of 16 VWB RSET (5) AD5227 ADJUSTABLE HIGH POWER LED DRIVER Figure 35 shows a circuit that can drive three to four high power LEDs. ADP1610 is an adjustable boost regulator that provides the voltage headroom and current for the LEDs. The AD5227 and the op amp form an average gain of 12 feedback network that servos the RSET voltage and ADP1610’s FB pin 1.2 V band gap reference voltage. As the loop is set, the voltage across RSET is regulated around 0.1 V and adjusted by the digital potentiometer. I LED = VRSET AUTOMATIC LCD PANEL BACKLIGHT CONTROL With the addition of a photocell sensor, an automatic brightness control can be achieved. As shown in Figure 36, the resistance of the photocell changes linearly but inversely with the light output. The brighter the light output, the lower the photocell resistance and vice versa. The AD5227 sets the voltage level that is gained up by U2 to drive N1 to a desirable brightness. With the photocell acting as the variable feedback resistor, the change in the light output changes the R2 resistance, therefore causing U2 to drive N1 accordingly to regulate the output. This simple low cost implementation of the LED controller can compensate for the temperature and aging effects typically found in high power LEDs. Similarly, for power efficiency, a PWM signal can be applied at the gate of N2 to switch the LED on and off without any noticeable effect. 5V 5V R2 R1 1kΩ D1 PHOTOCELL 5V C1 1µF (6) C2 0.1µF RSET RSET should be small enough to conserve power but large enough to limit maximum LED current. R3 should also be used in parallel with AD5227 to limit the LED current within an achievable range. A wider current adjustment range is possible by lowering the R2 to R1 ratio, as well as changing R3 accordingly. V+ U1 AD5227 VDD A N1 – U2 AD8591 2N7002 W + 10kΩ CLK C3 0.1µF 5V CS WHITE LED V– SD B U/D GND 04419-0-038 The U1 ADP3333ARM-1.5 is a 1.5 V LDO that is lifted above or lowered below 0 V. When VWB of the AD5227 is at minimum, there is no current through D1, so the GND pin of U1 would be at –1.5 V if U3 were biased with the dual supplies. As a result, some of the U2 low resistance steps have no effect on the output until the U1 GND pin is lifted above 0 V. When VWB of the AD5227 is at its maximum, VOUT becomes VL + VAB, so the U1 supply voltage must be biased with adequate headroom. Similarly, a PWM signal can be applied at the U1 shutdown pin for power efficiency. This circuit works well for a single LED. PWM Figure 36. Automatic LCD Panel Backlight Control 6-BIT CONTROLLER 5V R4 13.5kΩ U2 IN L1 10µF ADP1610 PWM SD 1.2V FB COMP RC 100kΩ CC 390pF SS VOUT SW D1 C3 10µF RT GND D2 CSS 10nF D3 C8 5V 0.1µF D4 U3 V+ The AD5227 can form a simple 6-bit controller with a clock generator, a comparator, and some output components. Figure 37 shows a generic 6-bit controller with a comparator that first compares the sampling output with the reference level and outputs either a high or low level to the AD5227 U/D pin. The AD5227 then changes step at every clock cycle in the direction indicated by the U/D state. Although this circuit is not as elegant as the one shown in Figure 36, it is self-contained, very easy to design, and can adapt to various applications. AD5227 VDD AD8541 U1 RSET 0.25Ω – V– CLK U1 AD5227 L1–SLF6025-100M1R0 D1–MBR0520LT1 R2 1.1kΩ U1 5V + W B A – U3 U/D B CS R1 100Ω GND AD8531 OUTPUT + OP AMP R3 200Ω 04419-0-037 10kΩ – + Figure 35. Adjustable Current Source for LEDs in Series SAMPLING_OUTPUT U2 COMPARATOR REF Figure 37. 6-Bit Controller Rev. 0 | Page 13 of 16 04419-0-039 C2 10µF AD5227 CONSTANT BIAS WITH SUPPLY TO RETAIN RESISTANCE SETTING 3.50 Users who consider EEMEM potentiometers but cannot justify the additional cost and programming for their designs can consider constantly biasing the AD5227 with the supply to retain the resistance setting as shown in Figure 38. The AD5227 is designed specifically with low power to allow power conservation even in battery-operated systems. As shown in Figure 39, a similar low power digital potentiometer is biased with a 3.4 V 450 mA/hour Li-Ion cell phone battery. The measurement shows that the device drains negligible power. Constantly biasing the potentiometer is a practical approach because most portable devices do not require detachable batteries for charging. Although the resistance setting of the AD5227 is lost when the battery needs to be replaced, this event occurs so infrequently that the inconvenience is minimal for most applications. 3.48 TA = 25°C VDD SW1 U1 U2 AD5227 VDD COMPONENT X COMPONENT Y GND GND + GND – GND 04419-0-040 BATTERY OR SYSTEM POWER VDD U3 VDD Figure 38. Constant Bias AD5227 for Resistance Retention Rev. 0 | Page 14 of 16 3.47 3.46 3.45 3.44 3.43 3.42 04419-0-041 BATTERY VOLTAGE (V) 3.49 3.41 3.40 0 2 4 6 DAYS 8 10 Figure 39. Battery Consumption Measurement 12 AD5227 OUTLINE DIMENSIONS 2.90 BSC 8 7 6 5 1 2 3 4 2.80 BSC 1.60 BSC PIN 1 0.65 BSC 0.90 0.87 0.84 1.95 BSC 1.00 MAX 0.10 MAX 0.38 0.22 0.20 0.08 8° 4° 0° SEATING PLANE 0.60 0.45 0.30 COMPLIANT TO JEDEC STANDARDS MO-193BA Figure 40. 8-Lead Small Outline Transistor Package TSOT-8 [Thin SOT-23-8] (UJ-8) Dimensions shown in millimeters ORDERING GUIDE Model AD5227BUJZ10-RL72 AD5227BUJZ10-R22 AD5227BUJZ50-RL72 AD5227BUJZ50-R22 AD5227BUJZ100-RL72 AD5227BUJZ100-R22 AD5227EVAL RAB 1kΩ) 10 10 50 50 100 100 10 Temperature Range −40°C to +105°C −40°C to +105°C −40°C to +105°C −40°C to +105°C −40°C to +105°C −40°C to +105°C Package Code UJ UJ UJ UJ UJ UJ Package Description TSOT-8 TSOT-8 TSOT-8 TSOT-8 TSOT-8 TSOT-8 Evaluation Board 1 Full Container Quantity 3000 250 3000 250 3000 250 1 Branding D3G D3G D3H D3H D3J D3J The end-to-end resistance RAB is available in 10 kΩ, 50 kΩ, and 100 kΩ versions. The final three characters of the part number determine the nominal resistance value, for example, 10 kΩ = 10. 2 Z = Pb-free part. Rev. 0 | Page 15 of 16 AD5227 NOTES © 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04419–0–3/04(0) Rev. 0 | Page 16 of 16