Low Power, Wide Supply Range, Low Cost Difference Amplifier, G = ½, 2 AD8278 FEATURES APPLICATIONS Voltage measurement and monitoring Current measurement and monitoring Instrumentation amplifier building block Portable, battery-powered equipment Test and measurement FUNCTIONAL BLOCK DIAGRAM +VS 7 AD8278 –IN 2 +IN 3 40kΩ 20kΩ 40kΩ 20kΩ 5 SENSE 6 OUT 1 REF 4 –VS 08308-001 Wide input range beyond supplies Rugged input overvoltage protection Low supply current: 200 μA maximum Low power dissipation: 0.5 mW at VS = 2.5 V Bandwidth: 1 MHz (G = ½) CMRR: 80 dB minimum, dc to 20 kHz (G = ½) Low offset voltage drift: ±2 μV/°C maximum (B Grade) Low gain drift: 1 ppm/°C maximum (B Grade) Enhanced slew rate: 1.4 V/μs Wide power supply range: Single supply: 2 V to 36 V Dual supplies: ±2 V to ±18 V 8-lead SOIC and MSOP packages Figure 1. Table 1. Difference Amplifiers by Category Low Distortion AD8270 AD8271 AD8273 AD8274 AMP03 1 High Voltage AD628 AD629 Current Sensing 1 AD8202 (U) AD8203 (U) AD8205 (B) AD8206 (B) AD8216 (B) Low Power AD8276 AD8277 U = unidirectional, B = bidirectional. GENERAL DESCRIPTION The AD8278 is a general-purpose difference amplifier intended for precision signal conditioning in power critical applications that require both high performance and low power. The AD8278 provides exceptional common-mode rejection ratio (80 dB) and high bandwidth while amplifying signals well beyond the supply rails. The on-chip resistors are laser-trimmed for excellent gain accuracy and high CMRR. They also have extremely low gain drift vs. temperature. The common-mode range of the amplifier extends to almost triple the supply voltage (for G = ½), making it ideal for singlesupply applications that require a high common-mode voltage range. The internal resistors and ESD circuitry at the inputs also provide overvoltage protection to the op amp. The AD8278 can be used as a difference amplifier with G = ½ or G = 2. It can also be connected in a high precision, singleended configuration for non-inverting and inverting gains of −½, −2, +3, +2, +1½, +1, or +½. The AD8278 provides an integrated precision solution that has a smaller size, lower cost, and better performance than a discrete alternative. The AD8278 operates on single supplies (2.0 V to 36 V) or dual supplies (±2 V to ±18 V). The maximum quiescent supply current is 200 μA, which makes it ideal for battery-operated and portable systems. The AD8278 is available in the space-saving 8-lead MSOP and SOIC packages. It is specified for performance over the industrial temperature range of −40°C to +85°C and is fully RoHS compliant. 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: 781.461.3113 ©2009 Analog Devices, Inc. All rights reserved. AD8278 TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characteristics ..............................................9 Applications ....................................................................................... 1 Theory of Operation ...................................................................... 16 Functional Block Diagram .............................................................. 1 Circuit Information.................................................................... 16 General Description ......................................................................... 1 Driving the AD8278................................................................... 16 Revision History ............................................................................... 2 Input Voltage Range ................................................................... 16 Specifications..................................................................................... 3 Power Supplies ............................................................................ 17 Absolute Maximum Ratings............................................................ 7 Applications Information .............................................................. 18 Thermal Resistance ...................................................................... 7 Configurations ............................................................................ 18 Maximum Power Dissipation ..................................................... 7 Instrumentation Amplifier........................................................ 19 Short-Circuit Current .................................................................. 7 Outline Dimensions ....................................................................... 20 ESD Caution .................................................................................. 7 Ordering Guide .......................................................................... 21 Pin Configurations and Function Descriptions ........................... 8 REVISION HISTORY 7/09—Revision 0: Initial Version Rev. 0 | Page 2 of 24 AD8278 SPECIFICATIONS VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted. Table 2. G=½ Parameter INPUT CHARACTERISTICS System Offset1 vs. Temperature Average Temperature Coefficient vs. Power Supply Common-Mode Rejection Ratio (RTI) Input Voltage Range2 Impedance3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% Settling Time to 0.001% GAIN Gain Error Gain Drift Gain Nonlinearity OUTPUT CHARACTERISTICS Output Voltage Swing4 Short-Circuit Current Limit Capacitive Load Drive NOISE5 Output Voltage Noise POWER SUPPLY Supply Current6 vs. Temperature Operating Voltage Range7 TEMPERATURE RANGE Operating Range Conditions Grade B Typ Max Min 50 250 250 μV μV 0.3 1 2.5 2 5 5 μV/°C μV/V +3(VS − 1.5) 74 −3(VS + 0.1) 120 30 1 1.4 10 V step on output, CL = 100 pF 1.1 dB +3(VS − 1.5) V 120 30 kΩ kΩ 1 1.4 MHz V/μs 9 10 0.005 TA = −40°C to +85°C VOUT = 20 V p-p VS = ±15 V, RL = 10 kΩ TA = −40°C to +85°C −VS + 0.2 0.02 1 5 +VS − 0.2 0.01 −VS + 0.2 ±15 200 f = 0.1 Hz to 10 Hz f = 1 kHz Unit 100 100 80 −3(VS + 0.1) 1.1 Grade A Typ Max 50 TA = −40°C to +85°C TA = −40°C to +85°C VS = ±5 V to ±18 V VS = ±15 V, VCM = ±27 V, RS = 0 Ω Min 1.4 47 9 10 μs μs 0.05 5 10 % ppm/°C ppm +VS − 0.2 V mA pF ±15 200 1.4 47 50 50 μV p-p nV/√Hz μA μA V °C ±2 200 250 ±18 ±2 200 250 ±18 −40 +125 −40 +125 TA = −40°C to +85°C 1 Includes input bias and offset current errors, RTO (referred to output) The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of Operation for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 20 through Figure 23 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 24 and Figure 26 for details. 7 Unbalanced dual supplies can be used, such as −VS = −0.5 V and +VS = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference voltage. 2 Rev. 0 | Page 3 of 24 AD8278 VS = ±5 V to ±15 V, VREF = 0 V, TA = 25°C, RL = 10 kΩ connected to ground, G = 2 difference amplifier configuration, unless otherwise noted. Table 3. G=2 Parameter INPUT CHARACTERISTICS System Offset 1 vs. Temperature Average Temperature Coefficient vs. Power Supply Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% Settling Time to 0.001% GAIN Gain Error Gain Drift Gain Nonlinearity OUTPUT CHARACTERISTICS Output Voltage Swing 4 Short-Circuit Current Limit Capacitive Load Drive NOISE 5 Output Voltage Noise POWER SUPPLY Supply Current 6 vs. Temperature Operating Voltage Range 7 TEMPERATURE RANGE Operating Range Conditions Grade B Typ Max Min 100 500 500 μV μV 0.6 2 5 2 5 10 μV/°C μV/V +1.5(VS − 1.5) dB V 80 +1.5(VS − 1.5) −1.5(VS + 0.1) 120 30 550 1.4 10 V step on output, CL = 100 pF 1.1 120 30 kΩ kΩ 550 1.4 kHz V/μs 10 11 TA = −40°C to +85°C 0.005 0.02 1 VOUT = 20 V p-p 5 VS = ±15 V, RL = 10 kΩ TA = −40°C to +85°C −VS + 0.2 +VS − 0.2 0.01 −VS + 0.2 ±15 350 f = 0.1 Hz to 10 Hz f = 1 kHz 2.8 90 10 11 μs μs 0.05 5 10 % ppm/° C ppm +VS − 0.2 V ±15 350 2.8 90 95 mA pF 95 μV p-p nV/√Hz μA μA V °C ±2 200 250 ±18 ±2 200 250 ±18 −40 +125 −40 +125 TA = −40°C to +85°C Unit 200 200 86 −1.5(VS + 0.1) 1.1 Grade A Typ Max 100 TA = −40°C to +85°C TA = −40°C to +85°C VS = ±5 V to ±18 V VS = ±15 V, VCM = ±27 V, RS = 0 Ω Min 1 Includes input bias and offset current errors, RTO (referred to output). The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of Operation for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 20 through Figure 23 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 24 and Figure 26 for details. 7 Unbalanced dual supplies can be used, such as −VS = −0.5 V and +VS = +2 V. The positive supply rail must be at least 2 V above the negative supply and reference voltage. 2 Rev. 0 | Page 4 of 24 AD8278 VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = ½ difference amplifier configuration, unless otherwise noted. Table 4. G=½ Parameter INPUT CHARACTERISTICS System Offset 1 vs. Temperature Average Temperature Coefficient vs. Power Supply Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% GAIN Gain Error Gain Drift OUTPUT CHARACTERISTICS Output Swing 4 Short-Circuit Current Limit Capacitive Load Drive NOISE 5 Output Voltage Noise POWER SUPPLY Supply Current 6 Operating Voltage Range TEMPERATURE RANGE Operating Range Conditions Grade B Typ Max Min 75 250 250 μV μV 0.3 1 2.5 2 5 5 μV/°C μV/V 74 80 −3(VS + 0.1) +3(VS − 1.5) 74 −3(VS + 0.1) +3(VS − 1.5) dB V 120 30 kΩ kΩ 870 1.3 870 1.3 kHz V/μs 7 7 μs 0.005 −VS + 0.1 0.02 1 +VS − 0.15 0.01 −VS + 0.1 ±10 200 1.4 47 TA = −40°C to +85°C dB 120 30 TA = −40°C to +85°C f = 0.1 Hz to 10 Hz f = 1 kHz Unit 150 150 80 2 V step on output, CL = 100 pF, VS = 2.7 V RL = 10 kΩ , TA = −40°C to +85°C Grade A Typ Max 75 TA = −40°C to +85°C TA = −40°C to +85°C VS = ±5 V to ±18 V VS = 2.7 V, VCM = 0 V to 2.4 V, RS = 0 Ω VS = ±5 V, VCM = −10 V to +7 V, RS = 0 Ω Min 0.05 5 % ppm/°C +VS − 0.15 V mA pF ±10 200 1.4 47 50 50 μV p-p nV/√Hz 2.0 200 36 2.0 200 36 μA V −40 +125 −40 +125 °C 1 Includes input bias and offset current errors, RTO (referred to output). The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of Operation section for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 20 through Figure 23 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 25 and Figure 26 for details. 2 Rev. 0 | Page 5 of 24 AD8278 VS = +2.7 V to <±5 V, VREF = midsupply, TA = 25°C, RL = 10 kΩ connected to midsupply, G = 2 difference amplifier configuration, unless otherwise noted. Table 5. G=2 Parameter INPUT CHARACTERISTICS System Offset 1 vs. Temperature Average Temperature Coefficient vs. Power Supply Common-Mode Rejection Ratio (RTI) Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% GAIN Gain Error Gain Drift OUTPUT CHARACTERISTICS Output Swing 4 Short-Circuit Current Limit Capacitive Load Drive NOISE 5 Output Voltage Noise POWER SUPPLY Supply Current 6 Operating Voltage Range TEMPERATURE RANGE Operating Range Conditions Grade B Typ Max Min 150 500 500 μV μV 0.6 2 5 3 5 10 μV/°C μV/V 80 86 −1.5(VS + 0.1) dB 80 +1.5(VS − 1.5) −1.5(VS + 0.1) dB +1.5(VS − 1.5) V 120 30 120 30 kΩ kΩ 450 1.3 450 1.3 kHz V/μs 9 9 μs 0.005 TA = −40°C to +85°C −VS + 0.1 0.02 1 +VS − 0.15 0.01 −VS + 0.1 ±10 200 f = 0.1 Hz to 10 Hz f = 1 kHz Unit 300 300 86 2 V step on output, CL = 100 pF, VS = 2.7 V RL = 10 kΩ, TA = −40°C to +85°C Grade A Typ Max 150 TA = −40°C to +85°C TA = −40°C to +85°C VS = ±5 V to ±18 V VS = 2.7 V, VCM = 0 V to 2.4 V, RS = 0 Ω VS = ±5 V, VCM = −10 V to +7 V, RS = 0 Ω Min 2.8 94 TA = −40°C to +85°C 0.05 5 % ppm/°C +VS − 0.15 V mA pF ±10 200 2.8 94 100 100 μV p-p nV/√Hz 2.0 200 36 2.0 220 36 μA V −40 +125 −40 +125 °C 1 Includes input bias and offset current errors, RTO (referred to output). The input voltage range may also be limited by absolute maximum input voltage or by the output swing. See the Input Voltage Range section in the Theory of Operation section for details. 3 Internal resistors are trimmed to be ratio matched and have ±20% absolute accuracy. 4 Output voltage swing varies with supply voltage and temperature. See Figure 20 through Figure 23 for details. 5 Includes amplifier voltage and current noise, as well as noise from internal resistors. 6 Supply current varies with supply voltage and temperature. See Figure 25 and Figure 26 for details. 2 Rev. 0 | Page 6 of 24 AD8278 ABSOLUTE MAXIMUM RATINGS 2.0 Table 6. THERMAL RESISTANCE SOIC θJA = 121°C/W 1.2 0.8 MSOP θJA = 135°C/W 0.4 0 –50 –25 0 25 50 75 100 125 AMBIENT TEMERATURE (°C) Figure 2. Maximum Power Dissipation vs. Ambient Temperature SHORT-CIRCUIT CURRENT The AD8278 has built-in, short-circuit protection that limits the output current (see Figure 27 for more information). While the short-circuit condition itself does not damage the part, the heat generated by the condition can cause the part to exceed its maximum junction temperature, with corresponding negative effects on reliability. Figure 2 and Figure 27, combined with knowledge of the supply voltages and ambient temperature of the part can be used to determine whether a short circuit will cause the part to exceed its maximum junction temperature. The θJA values in Table 7 assume a 4-layer JEDEC standard board with zero airflow. Table 7. Thermal Resistance θJA 135 121 1.6 08308-002 Rating ±18 V −VS + 40 V +VS − 40 V −65°C to +150°C −40°C to +85°C 150°C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; 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. Package Type 8-Lead MSOP 8-Lead SOIC MAXIMUM POWER DISSIPATION (W) TJ MAX = 150°C Parameter Supply Voltage Maximum Voltage at Any Input Pin Minimum Voltage at Any Input Pin Storage Temperature Range Specified Temperature Range Package Glass Transition Temperature (TG) Unit °C/W °C/W MAXIMUM POWER DISSIPATION The maximum safe power dissipation for the AD8278 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150°C, which is the glass transition temperature, the properties of the plastic change. Even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the parametric performance of the amplifiers. Exceeding a temperature of 150°C for an extended period may result in a loss of functionality. ESD CAUTION Rev. 0 | Page 7 of 24 AD8278 8 NC REF 1 AD8278 7 –IN 2 TOP VIEW (Not to Scale) +VS 6 OUT 5 SENSE –IN 2 +IN 3 –VS 4 NC = NO CONNECT NC 7 +VS 6 OUT 5 SENSE Figure 4. SOIC Pin Configuration Table 8. Pin Function Descriptions Mnemonic REF −IN +IN −VS SENSE OUT +VS NC 8 NC = NO CONNECT Figure 3. MSOP Pin Configuration Pin No. 1 2 3 4 5 6 7 8 AD8278 TOP VIEW +IN 3 (Not to Scale) –VS 4 08308-003 REF 1 08308-004 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS Description Reference Voltage Input. Inverting Input. Noninverting Input. Negative Supply. Sense Terminal. Output. Positive Supply. No Connect. Rev. 0 | Page 8 of 24 AD8278 TYPICAL PERFORMANCE CHARACTERISTICS VS = ±15 V, TA = 25°C, RL = 10 kΩ connected to ground, G = ½ difference amplifier configuration, unless otherwise noted. 600 80 N = 3840 MEAN = –16.8 SD = 41.7673 60 500 SYSTEM OFFSET (µV) NUMBER OF HITS 40 400 300 200 20 0 –20 –40 –60 100 –150 –100 –50 0 50 100 REPRESENTATIVE DATA –100 –50 –35 –20 –5 10 08308-005 0 150 SYSTEM OFFSET VOLTAGE (µV) Figure 5. Distribution of Typical System Offset Voltage, G = 2 800 40 55 70 85 Figure 8. System Offset vs. Temperature, Normalized at 25°, G = ½ 20 N = 3837 MEAN = 7.78 SD = 13.569 700 25 TEMPERATURE (°C) 08308-008 –80 15 10 GAIN ERROR (µV/V) NUMBER OF HITS 600 500 400 300 5 0 –5 –10 –15 200 –20 100 –20 0 20 40 60 REPRESENTATIVE DATA –30 –50 –35 –20 –5 10 CMRR (µV/V) Figure 6. Distribution of Typical Common-Mode Rejection, G = 2 40 55 70 85 Figure 9. Gain Error vs. Temperature, Normalized at 25°C, G = ½ 30 5 20 COMMON-MODE VOLTAGE (V) 10 0 –5 –10 –15 VS = ±15V 10 0 VS = ±5V –10 –20 REPRESENTATIVE DATA –20 –50 –35 –20 –5 10 25 40 55 70 85 TEMPERATURE (°C) –30 –20 08308-007 CMRR (µV/V) 25 TEMPERATURE (°C) –15 –10 –5 0 5 10 15 20 OUTPUT VOLTAGE (V) Figure 7. CMRR vs. Temperature, Normalized at 25°C, G = ½ Figure 10. Input Common-Mode Voltage vs. Output Voltage, ±15 V and ±5 V Supplies, G = ½ Rev. 0 | Page 9 of 24 08308-010 –40 08308-006 –60 08308-009 –25 0 AD8278 10 5 VREF = MIDSUPPLY VS = 5V VS = 5V 6 4 2 0 VS = 2.7V –2 –4 –6 2.5 3.5 4.5 5.5 1 12 –1 1.5 2.5 3.5 4.5 5.5 Figure 14. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = Midsupply, G = 2 6 VREF = 0V VS = 5V 5 COMMON-MODE VOLTAGE (V) VS = 5V 8 6 4 2 VS = 2.7V 0 0.5 OUTPUT VOLTAGE (V) VREF = 0V 10 –2 4 3 2 1 VS = 2.7V 0 1.5 2.5 3.5 4.5 5.5 OUTPUT VOLTAGE (V) –2 –0.5 08308-012 0.5 0.5 1.5 2.5 3.5 4.5 5.5 OUTPUT VOLTAGE (V) Figure 12. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = 0 V, G = ½ Figure 15. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = 0 V, G = 2 30 18 VS = ±15V 08308-015 –1 –4 12 20 6 GAIN = 2 0 0 GAIN (dB) 10 VS = ±5V –10 –6 GAIN = ½ –12 –18 –24 –20 –30 –20 –15 –10 –5 0 5 10 15 20 OUTPUT VOLTAGE (V) Figure 13. Input Common-Mode Voltage vs. Output Voltage, ±15 V and ±5 V Supplies, G = 2 –36 100 1k 10k 100k 1M FREQUENCY (Hz) Figure 16. Gain vs. Frequency, ±15 V Supplies Rev. 0 | Page 10 of 24 10M 08308-016 –30 08308-013 COMMON-MODE VOLTAGE (V) VS = 2.7V 0 –3 –0.5 Figure 11. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = Midsupply, G = ½ COMMON-MODE VOLTAGE (V) 2 08308-014 1.5 08308-011 0.5 OUTPUT VOLTAGE (V) –6 –0.5 3 –2 –8 –10 –0.5 VREF = MIDSUPPLY 4 COMMON-MODE VOLTAGE (V) COMMON-MODE VOLTAGE (V) 8 AD8278 18 +VS –0.1 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 12 GAIN = 2 6 GAIN = ½ –6 –12 –18 –24 –30 TA = –40°C TA = +25°C TA = +85°C TA = +125°C +0.4 +0.3 +0.2 100k 1M 10M –VS 2 4 6 8 10 12 14 18 16 SUPPLY VOLTAGE (±VS) 08308-020 10k 08308-017 1k FREQUENCY (Hz) Figure 20. Output Voltage Swing vs. Supply Voltage and Temperature, RL = 10 kΩ Figure 17. Gain vs. Frequency, +2.7 V Single Supply 120 +VS –0.2 100 GAIN = ½ 80 60 40 0 1 10 100 1k 10k 100k 1M FREQUENCY (Hz) –0.6 –0.8 –1.0 TA = –40°C TA = +25°C TA = +85°C TA = +125°C –1.2 +1.2 +1.0 +0.8 +0.6 +0.4 +0.2 –VS 08308-018 20 –0.4 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±VS) 08308-021 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES GAIN = 2 CMRR (dB) –0.4 +0.1 –36 100 Figure 21. Output Voltage Swing vs. Supply Voltage and Temperature, RL = 2 kΩ Figure 18. CMRR vs. Frequency +VS OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 120 100 –PSRR 80 60 +PSRR 40 20 0 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M 08308-019 PSRR (dB) –0.3 Figure 19. PSRR vs. Frequency –4 –8 TA = –40°C TA = +25°C TA = +85°C TA = +125°C +8 +4 –VS 1k 10k 100k LOAD RESISTANCE (Ω) Figure 22. Output Voltage Swing vs. RL and Temperature, VS = ±15 V Rev. 0 | Page 11 of 24 08308-022 GAIN (dB) 0 –0.2 AD8278 +VS 250 VREF = MIDSUPPLY 200 –1.0 SUPPLY CURRENT (µA) OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES –0.5 –1.5 –2.0 TA = –40°C TA = +25°C TA = +85°C TA = +125°C +2.0 +1.5 150 VS = ±15V 100 VS = +2.7V 50 +1.0 0 1 2 3 4 5 6 7 8 9 10 OUTPUT CURRENT (mA) 0 –50 08308-023 –VS –30 –10 10 30 50 70 90 110 130 110 130 TEMPERATURE (°C) Figure 23. Output Voltage Swing vs. IOUT and Temperature, VS = ±15 V 08308-026 +0.5 Figure 26. Supply Current vs. Temperature 180 30 25 SHORT-CIRCUIT CURRENT (mA) SUPPLY CURRENT (µA) 170 160 150 140 130 20 15 ISHORT+ 10 5 0 –5 –10 ISHORT– 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (±V) –20 –50 08308-024 120 –30 –10 10 Figure 24. Supply Current vs. Dual-Supply Voltage, VIN = 0 V 50 70 90 Figure 27. Short-Circuit Current vs. Temperature 180 2.0 –SLEW RATE 1.8 170 1.6 160 SLEW RATE (V/µs) SUPPLY CURRENT (µA) 30 TEMPERATURE (°C) 08308-027 –15 150 140 1.4 +SLEW RATE 1.2 1.0 0.8 0.6 0.4 130 5 10 15 20 25 SUPPLY VOLTAGE (V) 30 35 40 Figure 25. Supply Current vs. Single-Supply Voltage, VIN = 0 V, VREF = 0 V Rev. 0 | Page 12 of 24 0 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) Figure 28. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz 08308-028 0 08308-025 0.2 120 AD8278 8 4 1V/DIV 2 3.64µs TO 0.01% 4.12µs TO 0.001% 0 –2 0.002%/DIV –4 –6 4µs/DIV –4 –3 –2 –1 0 1 2 3 4 5 OUTPUT VOLTAGE (V) TIME (µs) 08308-029 –8 –5 Figure 29. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = ½ 08308-032 NONLINEARITY (2ppm/DIV) 6 Figure 32. Large-Signal Pulse Response and Settling Time, 2 V Step, VS = 2.7 V, G = ½ 8 4 5V/DIV 2 7.6µs TO 0.01% 9.68µs TO 0.001% 0 –2 0.002%/DIV –6 40µs/DIV –8 –6 –4 –2 0 2 4 6 8 10 OUTPUT VOLTAGE (V) TIME (µs) 08308-030 –8 –10 08308-033 –4 Figure 33. Large-Signal Pulse Response and Settling Time, 10 V Step, VS = ±15 V, G = 2 Figure 30. Gain Nonlinearity, VS = ±15 V, RL ≥ 2 kΩ, G = 2 5V/DIV 1V/DIV 6.24µs TO 0.01% 7.92µs TO 0.001% 4.34µs TO 0.01% 5.12µs TO 0.001% 0.002%/DIV 0.002%/DIV TIME (µs) 4µs/DIV 08308-031 40µs/DIV TIME (µs) Figure 31. Large-Signal Pulse Response and Settling Time, 10 V Step, VS = ±15 V, G = ½ Rev. 0 | Page 13 of 24 08308-034 NONLINEARITY (2ppm/DIV) 6 Figure 34. Large-Signal Pulse Response and Settling Time, 2 V Step, VS = 2.7 V AD8278 5.0 4.5 VS = ±5V 2V/DIV OUTPUT VOLTAGE (V p-p) 4.0 3.5 3.0 VS = ±2.5V 2.5 2.0 1.5 1.0 10µs/DIV 0 100 1k 10k 100k 1M FREQUENCY (Hz) 08308-038 08308-035 0.5 Figure 38. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V 5V/DIV 20mV/DIV Figure 35. Large-Signal Step Response, G = ½ 08308-036 RL = 200pF RL = 147pF RL = 247pF 10µs/DIV 40µs/DIV Figure 36. Large-Signal Step Response, G = 2 08308-039 NO LOAD Figure 39. Small-Signal Step Response for Various Capacitive Loads, G = ½ 30 VS = ±15V 20 20mV/DIV 15 10 VS = ±5V RL = 100pF RL = 200pF 5 RL = 247pF RL = 347pF 1k 10k FREQUENCY (Hz) 100k 1M 40µs/DIV 08308-037 0 100 Figure 37. Maximum Output Voltage vs. Frequency, VS = ±15 V, ±5 V 08308-040 OUTPUT VOLTAGE (V p-p) 25 Figure 40. Small-Signal Step Response for Various Capacitive Loads, G = 2 Rev. 0 | Page 14 of 24 AD8278 50 1k 45 40 ±2V ±5V NOISE (nV/ Hz) OVERSHOOT (%) 35 30 25 ±15V 20 ±18V 15 GAIN = 2 100 GAIN = ½ 10 0 50 100 150 200 250 CAPACITIVE LOAD (pF) 10 0.1 1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 41. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = ½ Figure 43. Voltage Noise Density vs. Frequency 35 GAIN = 2 30 ±2V 20 15 1µV/DIV OVERSHOOT (%) 25 ±5V GAIN = ½ ±15V 10 ±18V 0 50 100 150 200 250 CAPACITIVE LOAD (pF) 300 350 Figure 42. Small-Signal Overshoot vs. Capacitive Load, RL ≥ 2 kΩ, G = 2 Rev. 0 | Page 15 of 24 1s/DIV Figure 44. 0.1 Hz to 10 Hz Voltage Noise 08308-044 0 08308-042 5 08308-043 0 08308-041 5 AD8278 THEORY OF OPERATION CIRCUIT INFORMATION AC Performance The AD8278 consists of a low power, low noise op amp and four laser-trimmed on-chip resistors. These resistors can be externally connected to make a variety of amplifier configurations, including difference, noninverting, and inverting configurations. Taking advantage of the integrated resistors of the AD8278 provides the designer with several benefits over a discrete design, including smaller size, lower cost, and better ac and dc performance. Component sizes and trace lengths are much smaller in an IC than on a PCB, so the corresponding parasitic elements are also smaller. This results in better ac performance of the AD8278. For example, the positive and negative input terminals of the AD8278 op amp are intentionally not pinned out. By not connecting these nodes to the traces on the PCB, their capacitance remains low and balanced, resulting in improved loop stability and excellent common-mode rejection over frequency. +VS DRIVING THE AD8278 7 AD8278 20kΩ 20kΩ 40kΩ 5 SENSE 6 OUT 1 REF 4 –VS Care should be taken to drive the AD8278 with a low impedance source: for example, another amplifier. Source resistance of even a few kilohms (kΩ) can unbalance the resistor ratios and, therefore, significantly degrade the gain accuracy and commonmode rejection of the AD8278. Because all configurations present several kilohms (kΩ) of input resistance, the AD8278 does not require a high current drive from the source and so is easy to drive. INPUT VOLTAGE RANGE Figure 45. Functional Block Diagram DC Performance Much of the dc performance of op amp circuits depends on the accuracy of the surrounding resistors. Using superposition to analyze a typical difference amplifier circuit, as is shown in Figure 46, the output voltage is found to be ⎛ R2 ⎞⎛ ⎟ 1 + R4 ⎞⎟ − V IN − ⎛⎜ R4 ⎞⎟ VOUT = V IN + ⎜ ⎜ R1 + R2 ⎟⎜⎝ R3 ⎠ ⎝ R3 ⎠ ⎝ ⎠ The AD8278 is able to measure input voltages beyond the supply rails. The internal resistors divide down the voltage before it reaches the internal op amp, and provide protection to the op amp inputs. Figure 46 shows an example of how the voltage division works in a difference amplifier configuration. For the AD8278 to measure correctly, the input voltages at the input nodes of the internal op amp must stay below 1.5 V of the positive supply rail and can exceed the negative supply rail by 0.1 V. Refer to the Power Supplies section for more details. R2 (V ) R1 + R2 IN+ This equation demonstrates that the gain accuracy and commonmode rejection ratio of the AD8278 is determined primarily by the matching of resistor ratios. Even a 0.1% mismatch in one resistor degrades the CMRR to 69 dB for a G = 2 difference amplifier. R4 VIN– VIN+ R3 R1 R2 The difference amplifier output voltage equation can be reduced to VOUT R2 (V ) R1 + R2 IN+ R4 (VIN + − VIN − ) = R3 08308-046 +IN 3 40kΩ 08308-045 –IN 2 Figure 46. Voltage Division in the Difference Amplifier Configuration as long as the following ratio of the resistors is tightly matched: R2 R4 = R1 R3 The resistors on the AD8278 are laser trimmed to match accurately. As a result, the AD8278 provides superior performance over a discrete solution, enabling better CMRR, gain accuracy, and gain drift, even over a wide temperature range. The AD8278 has integrated ESD diodes at the inputs that provide overvoltage protection. This feature simplifies system design by eliminating the need for additional external protection circuitry, and enables a more robust system. The voltages at any of the inputs of the parts can safely range from +VS − 40 V up to −VS + 40 V. For example, on ±10 V supplies, input voltages can go as high as ±30 V. Care should be taken to not exceed the +VS − 40 V to −VS + 40 V input limits to avoid risking damage to the parts. Rev. 0 | Page 16 of 24 AD8278 The AD8278 operates extremely well over a very wide range of supply voltages. It can operate on a single supply as low as 2 V and as high as 36 V, under appropriate setup conditions. For best performance, the user must exercise care that the setup conditions ensure that the internal op amp is biased correctly. The internal input terminals of the op amp must have sufficient voltage headroom to operate properly. Proper operation of the part requires at least 1.5 V between the positive supply rail and the op amp input terminals. This relationship is expressed in the following equation: The AD8278 is typically specified at single- and dual-supplies, but it can be used with unbalanced supplies as well; for example, −VS = −5 V, +VS = 20 V. The difference between the two supplies must be kept below 36 V. The positive supply rail must be at least 2 V above the negative supply and reference voltage. R1 (V ) R1 + R2 REF R4 R3 R1 R2 VREF R1 (V ) R1 + R2 REF R1 V REF < + VS − 1.5 V R1 + R2 08308-046 POWER SUPPLIES Figure 47. Ensure Sufficient Voltage Headroom on the Internal Op Amp Inputs For example, when operating on a +VS= 2 V single supply and VREF = 0 V, it can be seen from Figure 47 that the op amps input terminals are biased at 0 V, allowing more than the required 1.5 V headroom. However, if VREF = 1 V under the same conditions, the input terminals of the op amp are biased at 0.66 V (G = ½). Now the op amp does not have the required 1.5 V headroom and can not function. Therefore, the user needs to increase the supply voltage or decrease VREF to restore proper operation. Use a stable dc voltage to power the AD8278. Noise on the supply pins can adversely affect performance. Place a bypass capacitor of 0.1 μF between each supply pin and ground, as close as possible to each supply pin. Use a tantalum capacitor of 10 μF between each supply and ground. It can be farther away from the supply pins and, typically, it can be shared by other precision integrated circuits. Rev. 0 | Page 17 of 24 AD8278 APPLICATIONS INFORMATION –IN The AD8278 can be configured in several ways, as a difference amplifier or a single-ended amplifier (see Figure 48 to Figure 54). All of these configurations have excellent gain accuracy and gain drift because they rely on the internal matched resistors. Note that Figure 50 shows the AD8278 as a difference amplifier with a midsupply reference voltage at the noninverting input. This allows the AD8278 to be used as a level shifter, which is appropriate in single-supply applications that are referenced to midsupply. Table 9 lists several single-ended amplifier configurations that are not illustrated. 5 20kΩ +IN 1 20kΩ 20kΩ IN 2 40kΩ 40kΩ 5 OUT 6 20kΩ 3 40kΩ VOUT = –½VIN Figure 52. Inverting Amplifier, Gain = −½ 1 2 40kΩ 5 OUT 1 20kΩ IN 2 OUT 6 20kΩ 6 Figure 48. Difference Amplifier, Gain = ½ 5 20kΩ 20kΩ OUT VOUT = ½(VIN+ − VIN−) –IN VREF = MIDSUPPLY Figure 51. Difference Amplifier, Gain = 2, Referenced to Midsupply 08308-047 3 40kΩ 3 VOUT = 2(VIN+ − VIN−) + VREF 5 6 +IN 40kΩ 08308-051 20kΩ OUT 3 40kΩ 08308-052 2 40kΩ 2 6 1 –IN 40kΩ 08308-050 CONFIGURATIONS VOUT = 1.5VIN Figure 53. Noninverting Amplifier, Gain = 1.5 40kΩ 3 5 20kΩ 40kΩ 08308-048 +IN 1 20kΩ VOUT = 2(VIN+ − VIN−) 2 6 OUT Figure 49. Difference Amplifier, Gain = 2 2 40kΩ 20kΩ IN 5 6 OUT 1 20kΩ 40kΩ 3 08308-053 –IN VOUT = 2VIN Figure 54. Noninverting Amplifier, Gain = 2 3 40kΩ 20kΩ VOUT = ½(VIN+ − VIN−) + VREF 1 VREF = MIDSUPPLY 08308-049 +IN Figure 50. Difference Amplifier, Gain = ½, Referenced to Midsupply Table 9. Difference and Single-Ended Amplifier Configurations Amplifier Configuration Difference Amplifier Difference Amplifier Single-Ended Inverting Amplifier Single-Ended Inverting Amplifier Single-Ended Non Inverting Amplifier Single-Ended Non Inverting Amplifier Single-Ended Non Inverting Amplifier Single-Ended Non Inverting Amplifier Single-Ended Non Inverting Amplifier Single-Ended Non Inverting Amplifier Signal Gain +½ +2 −½ −2 +3⁄2 +3 +½ +1 +1 +2 Pin 1 (REF) GND IN+ GND GND IN IN GND IN GND IN Rev. 0 | Page 18 of 24 Pin 2 (VIN−) IN− OUT IN OUT GND OUT GND GND OUT OUT Pin 3 (VIN+) IN+ GND GND GND IN IN IN GND IN GND Pin 5 (SENSE) OUT IN− OUT IN OUT GND OUT OUT GND GND AD8278 –IN As with the other inputs, the reference must be driven with a low impedance source to maintain the internal resistor ratio. An example using the low power, low noise OP1177 as a reference is shown in Figure 55. 40kΩ RF 20kΩ RG RF 40kΩ +IN REF AD8278 VOUT = (1 + 2RF/RG) (VIN+ – VIN–) × 2 Figure 56. Low Power Precision Instrumentation Amplifier REF V AD8278 REF A2 AD8278 VOUT 20kΩ CORRECT 08308-056 INCORRECT A1 V Table 10. Low Power Op Amps + Op Amp (A1, A2) AD8506 AD8607 AD8617 AD8667 – 08308-054 OP1177 Figure 55. Driving the Reference Pin INSTRUMENTATION AMPLIFIER The AD8278 can be used as a building block for a low power, low cost instrumentation amplifier. An instrumentation amplifier provides high impedance inputs and delivers high commonmode rejection. Combining the AD8278 with an Analog Devices, Inc., low power amplifier (see Table 10) creates a precise, power efficient voltage measurement solution suitable for power critical systems. Features Dual micropower op amp Precision dual micropower op amp Low cost CMOS micropower op amp Dual precision CMOS micropower op amp It is preferable to use dual op amps for the high impedance inputs, because they have better matched performance and track each other over temperature. The AD8278 difference amplifier cancels out common-mode errors from the input op amps, if they track each other. The differential gain accuracy of the in-amp is proportional to how well the input feedback resistors (RF) match each other. The CMRR of the in-amp increases as the differential gain is increased (1 + 2RF/RG), but a higher gain also reduces the common-mode voltage range. Note that dual supplies must be used for proper operation of this configuration. Refer to A Designer’s Guide to Instrumentation Amplifiers for more design ideas and considerations. Rev. 0 | Page 19 of 24 AD8278 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 5 1 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) COPLANARITY 0.10 SEATING PLANE 0.50 (0.0196) 0.25 (0.0099) 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-012-A A CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 57. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 3.20 3.00 2.80 8 3.20 3.00 2.80 1 5 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 COPLANARITY 0.10 45° 0.23 0.08 8° 0° SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 58. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. 0 | Page 20 of 24 0.80 0.60 0.40 012407-A 8 4.00 (0.1574) 3.80 (0.1497) AD8278 ORDERING GUIDE Model AD8278ARZ 1 AD8278ARZ-R71 AD8278ARZ-RL1 AD8278BRZ1 AD8278BRZ-R71 AD8278BRZ-RL1 AD8278ARMZ1 AD8278ARMZ-R71 AD8278ARMZ-RL1 AD8278BRMZ1 AD8278BRMZ-R71 AD8278BRMZ-RL1 1 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Package Description 8-Lead SOIC_N 8-Lead SOIC_N, 7" Tape and Reel 8-Lead SOIC_N, 13" Tape and Reel 8-Lead SOIC_N 8-Lead SOIC_N, 7" Tape and Reel 8-Lead SOIC_N, 13" Tape and Reel 8-Lead MSOP 8-Lead MSOP, 7" Tape and Reel 8-Lead MSOP, 13" Tape and Reel 8-Lead MSOP 8-Lead MSOP, 7" Tape and Reel 8-Lead MSOP, 13" Tape and Reel Z = RoHS Compliant Part. Rev. 0 | Page 21 of 24 Package Option R-8 R-8 R-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 RM-8 RM-8 RM-8 Branding Y21 Y21 Y21 Y22 Y22 Y22 AD8278 NOTES Rev. 0 | Page 22 of 24 AD8278 NOTES Rev. 0 | Page 23 of 24 AD8278 NOTES ©2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08308-0-7/09(0) Rev. 0 | Page 24 of 24