Choosing the Correct digiPOT for Your Application Analog Devices offers a wide range of digital potentiometer (digiPOT) options, including different memory technologies, single and dual supply, a variety of digital interfaces, high resolution devices, and the industry’s broadest end-to-end resistance options. What Is a digiPOT? A digiPOT is a digitally controlled device that can be used to adjust voltage or current and offers the same analog functions as a mechanical potentiometer or rheostat. This allows an automatic calibration process that is more accurate, more robust, and faster, with smaller voltage glitches. digiPOTs are often used for digital trimming and calibration of analog signals and are typically controlled by digital protocols, such as I2C and SPI, as well as more basic up/down and push-button protocols. A DIGITAL BLOCK Figure 1. 3-terminal digiPOT. ANALOG INPUTS/OUTPUTS W Architecture A digiPOT is a 3-terminal device (see Figure 1), with an internal architecture that is comprised of an array of resistances and switches. Each digiPOT consists of passive resistors in series between Terminals A and B. The wiper terminal, W, is digitally programmable to access any one of the 2n tap points on the resistor string. The resistance between Terminals A and B, RAB, is commonly called the end-to-end resistance. ADI offers a wide range of end-to-end resistor options spanning from 1 kΩ to 1 MΩ. The resistance between Terminals A and W, RAW, and the resistance between Terminals B and W, RWB, are complementary. That is, if RAW increases, then RWB will decrease in the same proportion. There is no restriction on the voltage polarity applied to Terminals A, B, or W. Voltage across the Terminals A to B, W to A, and W to B can be at either polarity— the only requirement is to ensure that the signal does not exceed the power supply rails. Similarly, there is no limitation in the current flow direction; the only restriction is that the maximum current does not exceed the current density specification, typically on the order of a few mA. B analog.com/digiPOTs Which digiPOT to Use? Typical Applications When choosing the correct digital potentiometer for your application, the key parameters to consider are • Wheatstone bridge calibration I. Resistor configuration V. End-to-end resistance II. Digital interface VI.Resolution III. Internal memory VII. Performance IV.Supply voltage VIII.Package • Op amp gain control (see Figure 5) • Analog filter tuning A A A digiPOT can be configured as a potentiometer or as a rheostat. Potentiometer Mode In this configuration, there are three terminals available: A, B, and W (see Figure 2). The digiPOT operates as a voltage divider, and the wiper terminal voltage is proportional to the voltage applied between the A and B terminals and the resistance at RAW and RWB. In Figure 3, a reference voltage is connected to Terminal A, and Terminal B is grounded. The voltage at the wiper pin can be calculated as VOUT = CODE 2n VOUT A W I. Resistor Configuration VIN W × VREF R W B RHEOSTAT B Figure 4. Rheostat. Figure 5. Noninverting amplifier. II. Digital Interface ADI’s large digiPOT portfolio supports a wide range of digital interfaces: • SPI — ADI offers SPI-compatible interfaces that can be operated at speeds up to 50 MHz clock rate. • I2C — ADI offers I2C-compatible interfaces that support standard and fast mode, up to a 400 kHz clock rate. Address pins are typically available, which allow the user to configure the slave address so that multiple devices can be operated on the same bus. • Push-Button — the user can interact directly with the system by just adding two push-button switches. Press the UP button to increment the resistance and DOWN to decrement resistance (see Figure 6). Typical Applications • DAC • LCD VCOM adjustment • Analog signal attenuation VREF • Up/Down — this is a simple interface, which can be operated by any host controller or discrete logic or manually with a rotary encoder or push buttons. With a single edge, resistance can be increased or decreased. A VDD W B UP BUTTON PU Figure 2. Potentiometer. Figure 3. DAC mode. R R PD DOWN BUTTON Rheostat Mode The digiPOT can operate as a digitally controlled rheostat where only two terminals are used. The unused terminal can be left floating or tied to the W terminal, as shown in Figure 4. The nominal end-to-end resistance (RAB) of the digiPOT has 2n contact points accessible by the wiper terminal, and the resulting resistance can be measured either across the wiper and B terminals (RWB) or across the wiper and A terminals (RAW). Figure 6. Push-button interface. III. Internal Memory The minimum wiper resistance is at the wiper’s first connection at the B terminal for zero scale. This B terminal connection has a minimum wiper contact resistance, RW, of typically 70 Ω. ADI’s wide portfolio supports four different options of integrated memory, allowing the user the flexibility to select the ideal digiPOT for the end application. Internal memory allows the user to set the wiper’s power-on reset (POR) position to a user programmed value. The wiper position can be reprogrammed multiple times but always returns to the programmed position on power-up. This function is ideal for calibration or for applications that require a fast power-on time. The rheostat resistance can be calculated by • Volatile memory only: digiPOT typically powers up to midscale. RAW = 2n – CODE 2n × RAB + RW or RWB = CODE 2n × RAB + RW • One-time programmable (OTP): allows user to program the wiper power-up position once — ideal for factory calibration. • Multitime programmable (MTP): ADI has product offerings that support 2×, 20×, or 50× programmable wiper memory. • EEPROM: ADI’s integrated EEPROM offers endurance up to 1M programming cycles and data retention of 50 years at 125°C. IV. Supply Voltage VII. Key Performance Parameters Before selecting a digiPOT for an application, it is important to understand the maximum signal voltage that will be applied to the A, B, or W terminals. The positive, VDD, and negative, VSS (or GND for a unipolar digiPOT), power supplies define the voltage signal boundary conditions. Signals that exceed VDD or VSS are typically clamped by internal forwardbiased diodes. Resistor Tolerance Error — digiPOT resistor tolerance error is the absolute end-to-end resistance error. This error is typically ±20% and can be a critical parameter if matching to an external discrete resistor or sensor in an open-loop application. Reducing the Impact of Resistor Tolerance Error • ADI offers digiPOTs, for example, the AD5272 and AD5292, with industry-leading maximum ±1% variable resistor performance. These devices enable designers to digitally program accurate resistor values, simplifying the process of determining the system error budget (see Figure 9). ADI’s large portfolio supports a wide range of supply options: • Single supply: 2.3 V to 33 V (see Figure 7) • Dual supply: ±2.25 V to ±16.5 V (see Figure 8) • Low resistor tolerance, for example, the AD5110, with a ±1% typical and ±8% maximum resistor tolerance. VIN +VDD A VIN W VOUT 0V • Products such as the AD5259 and AD5235 have the resistor tolerance error stored in the EEPROM memory. This allows the user to calculate the actual end-to-end resistance to an accuracy of 0.01%. VOUT VOFFSET 0V B VOFFSET • The new patented linear gain setting mode allows controlling the potentiometer as two independent rheostats, RAW and RWB, connected in a single point, W terminal (see Figure 10). This mode is ideal in equations where the output depends on the ratio of two resistors, G = R1/R2, for example, in an inverting amplifier. This mode can be found in the AD5141, offering a maximum ratio error below ±1%. Figure 7. AC signal, single-supply mode. VIN A +VDD +VDD VIN 0V W –VSS VOUT 0V VOUT –VSS B 4 +IN RDAC Figure 8. AC signal, dual-supply mode. RG IN-AMP –IN V. End-to-End Resistance VREF GAIN = 1 + ADI offers a wide range of end-to-end resistor options, from 1 kΩ to 1 MΩ. This simplifies the task of achieving the optimum impedance, power dissipation, bandwidth, and noise performance combination. Resistance (𝛀) 1k 2.5k 5k Resolution (Taps) 32 • 128 1024 10k 20k 25k 50k 80k 100k 200k 250k 1M • • • • • • • • • • • • • • • • • • • • • • • 2 1 0 0 200 400 600 800 1000 DECIMAL CODE ENABLE RDAC REGISTER AW A A RAW RAW RAW = RAB – RWB W Table 1. Quick Reference Resistance Options • RG DISABLE ADI has offerings ranging from 5-bit to 10-bit resolution offering LSB step sizes as low as 4 Ω. If more resolution is required, then a cascade, serial, or parallel combination of digiPOTs can be implemented (see Table 1). 256 49.400 3 Figure 9. Instrumentation amplifier. VI. Resolution 64 VOUT ERROR (%) +VDD VOFFSET RDAC REGISTER WB B RAB = RAW + RWB RWB RDAC REGISTER WB W B RWB Figure 10. Linear gain setting mode. • • • digiPOT Temperature Coefficient — ADI’s digiPOTs leverage proprietary thin film resistor technology, leading to the lowest temperature coefficient performance available on the market (for example, AD5292): • 5 ppm/°C in potentiometer mode • 35 ppm/°C in rheostat mode Bandwidth — the digiPOT architecture is comprised of resistors and switches (see Figure 11). The resistance of the resistors in the path of a particular code, combined with the switch parasitic, pin, and board capacitances, creates an RC low-pass filter, which determines the maximum ac frequency that can be passed through the digiPOT before it is attenuated by more than –3 dB. Choosing a low end-to-end resistor option will support a higher –3 dB bandwidth (see Table 2). Applications AUDIO_INPUT PUSH-UP BUTTON PU PD PUSH-DOWN BUTTON A W – B + Table 2. Typical –3 dB Bandwidth vs. Resistor Option Resistance 1 kΩ 5 kΩ 10 kΩ 50 kΩ 100 kΩ 1 MΩ Frequency 5 MHz 2 MHz 1 MHz 120 kHz 70 kHz 6 kHz Figure 13. Audio volume control with an amplifier and push-button interface. VIN SA RL VDD +15V A RL SW SERIAL INTERFACE AD5292 A W RS VOUT B W SB RS GND –15V Figure 14. Logarithmic pro audio volume control. RL B VSS RL Figure 11. Internal architecture. THD — an ac signal applied to the terminals of a digiPOT will cause variation in the internal switch, RON, leading to some nonsymmetrical attenuation and, therefore, signal distortion (see Figure 12). Choosing a high end-to-end resistor option reduces the contribution of the internal switches’ resistance vs. the total resistance, leading to better THD performance. Table 3 shows some typical THD performance values. VIN VOUT Figure 15. Variable low-pass Sallen-Key filter. Table 3. Typical THD Performance of the AD5292 Resistance 20 kΩ 50 kΩ 100 kΩ THD –93 dB –101 dB –106 dB SIGNAL DISTORTION INPUT SIGNAL PMOS VOUT VIN SERIAL INTERFACE NMOS ATTENUATION IDEAL OUTPUT SIGNAL REAL OUTPUT SIGNAL Figure 16. Programmable voltage source with current booster. Figure 12. Total harmonic distortion. VIII. Packages ADI digiPOTs are available in a wide range of packages: • SC70 • MSOP • LFCSP • TSSOP • SOT-23 • SOIC Reference circuit designs are engineered and tested for quick and easy system integration to help solve today’s relevant design challenges. Visit the circuit library where you can find digiPOT circuit designs at www.analog.com/circuits. Nonvolatile Memory Digital Potentiometers Part Number Resolution (Number of Wiper Steps) One Time Programmable Memory (OTP) AD5273 64 AD5171 64 AD5172 256 AD5173 256 Multitime Programmable Memory (MTP) AD5271 AD5291 AD5170 AD5274 AD5270 AD5174 AD5292 AD5272 AD5175 EEPROM AD5114 New AD5115 New AD5112 New AD5113 New AD5116 New AD5258 AD5110 New AD5111 New AD5121 New AD5259 AD5141 New AD5231 AD5251 AD5122A New AD5122 New AD5232 AD5252 AD5142A New AD5142 New AD5235 ADN2850 AD5233 AD5253 AD5123 New AD5124 New AD5254 AD5143 New AD5144A New AD5144 New TP = times programmable *Linear gain setting mode † 256 256 256 256 1024 1024 1024 1024 1024 32 32 64 64 64 64 128 128 128 256 256 1024 64 128 128 256 256 256 256 1024 1024 64 64 128 128 256 256 256 256 Number of Channels 1 2 1 1 2 4 Maximum Terminal Voltage Range (V) Interface Nominal Resistance (k𝛀) Absolute Tempco (ppm/°C) Package Leads Price @ 1k ($U.S.) 5.5 5.5 5.5 5.5 I2C I2C I2C I2C 1, 10, 50, 100 5, 10, 50, 100 2.5, 10, 50, 100 2.5, 10, 50, 100 300 35 35 35 8-lead SOT-23 8-lead SOT-23 10-lead MSOP 10-lead MSOP 0.69 0.72 1.32 1.32 1 kΩ option has high bandwidth Tempco is 5 ppm/°C in potentiometer mode Tempco is 15 ppm/°C in potentiometer mode Additional address pins (AD0 and AD1) ±2.75, +5.5 ±16.5, +33 5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±16.5, +33 ±2.75, +5.5 ±2.75, +5.5 SPI SPI I2C I2C SPI SPI SPI I2C I2C 20, 100 20, 50, 100 2.5, 10, 50, 100 20, 100 20, 50, 100 10 20, 50, 100 20, 50, 100 10 35 35 35 35 35 35 35 35 35 10-lead LFCSP, 10-lead MSOP 14-lead TSSOP 10-lead MSOP 10-lead LFCSP, 10-lead MSOP 10-lead LFCSP, 10-lead MSOP 10-lead LFCSP, 10-lead MSOP 14-lead TSSOP 10-lead LFCSP, 10-lead MSOP 10-lead LFCSP, 10-lead MSOP 0.95 2.29 1.00 0.95 1.59 1.45 2.62 1.59 1.45 1% R-tol, 50 TP,† internal fuse programming supply High voltage, 1% R-tol, 20 TP,† internal fuse programming supply, low THD 2-TP† 1% R-tol, 50 TP,† internal fuse programming supply 1% R-tol, 50 TP,† internal fuse programming supply 50 TP,† internal fuse programming supply High voltage, 1% R-tol, 20 TP,† internal fuse programming supply, low THD 1% R-tol, 50 TP,† internal fuse programming supply 50 TP,† internal fuse programming supply 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 ±2.75, +5.5 5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 ±2.75, +5.5 I2C Up/down I2C Up/down Push-button I2C I2C Up/down SPI/I2C I2C SPI/I2C SPI I2C I2C SPI SPI I2C I2C SPI SPI SPI SPI I2C I2C SPI/I2C I2C I2C I2C SPI/I2C 10, 80 10, 80 5, 10, 80 5, 10, 80 5, 10, 80 1, 10, 50, 100 10, 80 10, 80 10, 100 5, 10, 50, 100 10, 100 10, 50, 100 1, 10, 50, 100 10, 100 10, 100 10, 50, 100 1, 10, 50, 100 10, 100 10, 100 25, 250 25, 250 10, 50, 100 1, 10, 50, 100 10, 100 10, 100 1, 10, 50, 100 10, 100 10, 100 10, 100 35 35 35 35 35 300 35 35 35 300 35 600 600 35 35 300 300 35 35 35 35 600 300 35 35 300 35 35 35 8-lead LFCSP 8-lead LFCSP 8-lead LFCSP 8-lead LFCSP 8-lead LFCSP 10-lead MSOP 8-lead LFCSP 8-lead LFCSP 16-lead LFCSP 10-lead LFCSP, 10-lead MSOP 16-lead LFCSP 16-lead TSSOP 14-lead TSSOP 16-lead LFCSP, 16-lead TSSOP 16-lead LFCSP, 16-lead TSSOP 16-lead TSSOP 14-lead TSSOP 16-lead LFCSP, 16-lead TSSOP 16-lead LFCSP, 16-lead TSSOP 16-lead TSSOP 16-lead LFCSP, 16-lead TSSOP 24-lead TSSOP 20-lead TSSOP 16-lead LFCSP 24-lead LFCSP, 20-lead TSSOP 20-lead TSSOP 16-lead LFCSP 20-lead TSSOP 24-lead LFCSP, 20-lead TSSOP 0.60 0.60 0.68 0.68 0.66 0.59 0.76 0.76 0.70 0.9 0.90 1.97 1.97 1.45 1.45 2.40 1.61 1.65 1.65 3.52 3.52 2.50 2.49 2.45 2.50 2.58 2.85 2.90 2.90 8% R-tol; 2.3 V supply operation, low power consumption 8% R-tol; 2.3 V supply operation, low power consumption 8% R-tol; 2.3 V supply operation, low power consumption 8% R-tol; tempco is 5 ppm/°C in potentiometer mode 8% R-tol; 2.3 V supply operation, low power consumption % R-tol error stored in NVM 8% R-tol; 2.3 V supply operation, low power consumption 8% R-tol; 2.3 V supply operation, low power consumption LGST,* 8% R-tol; 2.3 V supply operation % R-tol error stored in NVM LGST,* 8% R-tol; 2.3 V supply operation 28 bytes of user-programmable NVM % R-tol error stored in NVM, 12 bytes of user-programmable NVM LGST,* 8% R-tol; 2.3 V supply operation LGST,* 8% R-tol; 2.3 V supply operation 14 bytes of user-programmable NVM % R-tol error stored in NVM, 12 bytes of user-programmable NVM LGST,* 8% R-tol; 2.3 V supply operation LGST,* 8% R-tol; 2.3 V supply operation % R-tol error stored in NVM, 26 bytes of user-programmable NVM % R-tol error stored in NVM, 26 bytes of user-programmable NVM 11 bytes of user-programmable NVM % R-tol error stored in NVM, 12 bytes of user-programmable NVM LGST,* 8% R-tol; 2.3 V supply operation LGST,* 8% R-tol; 2.3 V supply operation % R-tol error stored in NVM, 12 bytes of user-programmable NVM LGST,* 8% R-tol; 2.3 V supply operation LGST,* 8% R-tol; 2.3 V supply operation LGST,* 8% R-tol; 2.3 V supply operation Comments BR09271-.5-10/14(B) ©2014 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. Printed in the U.S.A. Volatile Digital Potentiometers Part Number Resolution (Number of Wiper Steps) Number of Channels Maximum Terminal Voltage Range (V) Interface Nominal Resistance (k𝛀) Absolute Tempco (ppm/°C) Package Leads Price @ 1k ($U.S.) Comments analog.com/digiPOTs AD5228 32 5.5 Push-button 10, 50, 100 35 8-lead TSOT 0.34 Manual with built-in debouncer AD5201 33 ±2.75, +5.5 SPI 10, 50 500 10-lead MSOP 0.50 Low wiper resistance AD5227 64 5.5 Up/down 10, 50, 100 35 8-lead TSOT 0.36 Tempco is 10 ppm/°C in potentiometer mode AD5246 128 5.5 I2C 5, 10, 50, 100 35 6-lead SC70 0.45 Ultracompact, rheostat only AD5247 128 5.5 I2C 5, 10, 50, 100 35 6-lead SC70 0.45 Ultracompact AD5220 128 5.5 Up/down 10, 50, 100 800 8-lead MSOP, 8-lead SOIC 0.90 AD7376 128 ±16.5, +33 SPI 10, 50, 100 300 14-lead TSSOP, 16-lead SOIC 2.86 AD5160 256 5.5 SPI 5, 10, 50, 100 35 8-lead SOT-23 0.64 AD5165 256 5.5 SPI 100 35 8-lead TSOT 0.58 AD5245 256 5.5 I2C 5, 10, 50, 100 35 8-lead SOT-23 0.64 AD5161 256 5.5 SPI 5, 10, 50, 100 35 10-lead MSOP 0.65 AD5241 256 ±2.75, +5.5 I2C 10, 100, 1000 30 14-lead TSSOP, 14-lead SOIC 0.93 AD5200 256 ±2.75, +5.5 SPI 10, 50 500 10-lead MSOP 0.89 AD8400 256 5.5 SPI 1, 10, 50, 100 500 8-lead SOIC 1.13 AD5260 256 ±5.5, +16.5 SPI 20, 50, 200 35 14-lead TSSOP 1.80 AD5280 256 ±5.5, +16.5 I2C 20, 50, 200 35 14-lead TSSOP 1.80 AD5290 256 ±16.5, +33 SPI 10, 50, 100 35 10-lead MSOP 1.97 High voltage AD5293 1024 ±16.5, +33 SPI 20, 50, 100 35 14-lead TSSOP 2.55 High voltage, 1% R-tol, low THD 0.80 1 High voltage Low power: 0.05 μA 1 kΩ option has high bandwidth AD5222 128 ±2.75, +5.5 Up/down 10, 50, 100, 1000 35 14-lead TSSOP, 14-lead SOIC AD5162 256 5.5 SPI 2.5, 10, 50, 100 35 10-lead MSOP 1.00 AD5207 256 ±2.75, +5.5 SPI 10, 50, 100 500 14-lead TSSOP 1.06 AD8402 replacement AD8402 256 5.5 SPI 1, 10, 50, 100 500 14-lead TSSOP, 14-lead SOIC 1.68 1 kΩ option has high bandwidth 1 rheostat, 1 potentiometer AD5262 256 ±5.5, +16.5 SPI 20, 50, 200 35 16-lead TSSOP 1.97 AD5243 256 5.5 I2C 2.5, 10, 50, 100 35 10-lead MSOP 1.00 Rheostat/potentiometer AD5248 256 5.5 I2C 2.5, 10, 50, 100 35 10-lead MSOP 1.00 Rheostats only AD5242 256 ±2.75, +5.5 I2C 10, 100, 1000 30 16-lead TSSOP, 16-lead SOIC 1.27 AD5282 256 ±5.5, +16.5 I2C 20, 50, 200 35 16-lead TSSOP 1.97 AD5203 64 5.5 SPI 10, 100 700 24-lead TSSOP, 24-lead SOIC 1.47 AD5204 256 ±2.75, +5.5 SPI 10, 50, 100 700 32-lead LFCSP, 24-lead TSSOP, 24-lead SOIC 1.52 Preset to midscale/zero-scale pin AD8403 256 5.5 SPI 1, 10, 50, 100 500 24-lead TSSOP, 24-lead SOIC 2.79 1 kΩ option has high bandwidth AD5263 256 ±7.5, +16.5 SPI/I2C 20, 50, 200 30 24-lead TSSOP 2.58 Additional I2C address pins (AD0 and AD1) AD5206 256 ±2.75, +5.5 SPI 10, 50, 100 700 24-lead TSSOP, 24-lead SOIC 1.94 Preset to midscale/zero-scale pin 2 4 6 Analog Devices, Inc. Worldwide Headquarters Analog Devices, Inc. One Technology Way P.O. Box 9106 Norwood, MA 02062-9106 U.S.A. Tel: 781.329.4700 (800.262.5643, U.S.A. only) Fax: 781.461.3113 Analog Devices, Inc. Europe Headquarters Analog Devices, Inc. Wilhelm-Wagenfeld-Str. 6 80807 Munich Germany Tel: 49.89.76903.0 Fax: 49.89.76903.157 Analog Devices, Inc. Japan Headquarters Analog Devices, KK New Pier Takeshiba South Tower Building 1-16-1 Kaigan, Minato-ku, Tokyo, 105-6891 Japan Tel: 813.5402.8200 Fax: 813.5402.1064 Analog Devices, Inc. Asia Pacific Headquarters Analog Devices 5F, Sandhill Plaza 2290 Zuchongzhi Road Zhangjiang Hi-Tech Park Pudong New District Shanghai, China 201203 Tel: 86.21.2320.8000 Fax: 86.21.2320.8222