 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| Low Power, Wide Supply Range, Low Cost Unity-Gain Difference Amplifiers AD8276/AD8277 FEATURES Wide input range beyond supplies Rugged input overvoltage protection Low supply current: 200 A maximum per channel Low power dissipation: 0.5 mW at VS = 2.5 V Bandwidth: 550 kHz CMRR: 86 dB minimum, dc to 10 kHz Low offset voltage drift: 2 V/C maximum (B Grade) Low gain drift: 1 ppm/C maximum (B Grade) Enhanced slew rate: 1.1 V/s Wide power supply range: Single supply: 2 V to 36 V Dual supplies: 2 V to 18 V FUNCTIONAL BLOCK DIAGRAM +VS 7 AD8276 -IN 2 40k 40k 5 SENSE 6 OUT +IN 3 40k 40k 1 REF 07692-001 4 -VS Figure 1. AD8276 +VS 11 APPLICATIONS Voltage measurement and monitoring Current measurement and monitoring Differential output instrumentation amplifier Portable, battery-powered equipment Test and measurement -INA 2 40k AD8277 40k 12 SENSEA 13 OUTA +INA 3 40k 40k 14 REFA GENERAL DESCRIPTION The AD8276/AD8277 are general-purpose, unity-gain difference amplifiers intended for precision signal conditioning in power critical applications that require both high performance and low power. They provide exceptional common-mode rejection ratio (86 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 amplifiers extends to almost double the supply voltage, making these amplifiers 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 amps. The AD8276/AD8277 are unity-gain stable. While they are optimized for use as difference amplifiers, they can also be connected in high precision, single-ended configurations with G = -1, +1, +2. The AD8276/AD8277 provide an integrated precision solution that has smaller size, lower cost, and better performance than a discrete alternative. The AD8276/AD8277 operate on single supplies (2.0 V to 36 V) or dual supplies (2 V to 18 V). The maximum quiescent supply current is 200 A per channel, which is ideal for batteryoperated and portable systems. -INB 6 40k 40k 10 SENSEB 9 OUTB +INB 5 40k 40k 8 REFB 07692-052 4 -VS Figure 2. AD8277 Table 1. Difference Amplifiers by Category Low Distortion AD8270 AD8271 AD8273 AD8274 AMP03 1 High Voltage AD628 AD629 Current Sensing1 AD8202 (U) AD8203 (U) AD8205 (B) AD8206 (B) AD8216 (B) Low Power AD8276 AD8277 AD8278 U = unidirectional, B = bidirectional. The AD8276 is available in the space-saving 8-lead MSOP and SOIC packages, and the AD8277 is offered in a 14-lead SOIC package. Both are specified for performance over the industrial temperature range of -40C to +85C and are fully RoHS compliant. Rev. A 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 (c)2009 Analog Devices, Inc. All rights reserved. AD8276/AD8277 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...................................................................... 5 Maximum Power Dissipation ..................................................... 5 Short-Circuit Current .................................................................. 5 ESD Caution .................................................................................. 5 Pin Configurations and Function Descriptions ........................... 6 Typical Performance Characteristics ............................................. 8 Theory of Operation ...................................................................... 14 Circuit Information.................................................................... 14 Driving the AD8276/AD8277 .................................................. 14 Input Voltage Range ................................................................... 14 Power Supplies ............................................................................ 15 Applications Information .............................................................. 16 Configurations ............................................................................ 16 Differential Output .................................................................... 16 Current Source............................................................................ 17 Voltage and Current Monitoring.............................................. 17 Instrumentation Amplifier........................................................ 18 RTD .............................................................................................. 18 Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 20 REVISION HISTORY 7/09--Rev. 0 to Rev. A Added AD8277 ................................................................... Universal Changes to Features Section............................................................ 1 Changes to General Description Section ...................................... 1 Added Figure 2; Renumbered Sequentially .................................. 1 Changes to Specifications Section .................................................. 3 Changes to Figure 3 and Table 5 ..................................................... 5 Added Figure 5 and Table 7; Renumbered Sequentially ............. 7 Changes to Figure 10 ........................................................................ 8 Changes to Figure 34 ...................................................................... 12 Added Figure 36.............................................................................. 13 Changes to Input Voltage Range Section .................................... 14 Changes to Power Supplies Section and Added Figure 40........ 15 Added to Figure 40 ......................................................................... 15 Changes to Differential Output Section ...................................... 16 Added Figure 47 and Changes to Current Source Section ....... 17 Added Voltage and Current Monitoring Section and Figure 49..... 17 Moved Instrumentation Amplifier Section and Added RTD Section ........................................................................................................ 18 Changes to Ordering Guide .......................................................... 20 5/09--Revision 0: Initial Version Rev. A | Page 2 of 20 AD8276/AD8277 SPECIFICATIONS VS = 5 V to 15 V, VREF = 0 V, TA = 25C, RL = 10 k connected to ground, G = 1 difference amplifier configuration, unless otherwise noted. Table 2. G=1 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% Channel Separation 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 1 2 Conditions Min Grade B Typ Max 100 200 200 2 5 Min Grade A Typ Max 100 500 500 5 10 Unit V V V/C V/V dB V k k kHz V/s TA = -40C to +85C TA = -40C to +85C VS = 5 V to 18 V VS = 15 V, VCM = 27 V, RS = 0 0.5 2 86 -2(VS + 0.1) 80 40 550 1.1 +2(VS - 1.5) 80 -2(VS + 0.1) 80 40 550 1.1 +2(VS - 1.5) 0.9 10 V step on output, CL = 100 pF f = 1 kHz 0.9 15 16 15 16 130 130 0.005 0.02 1 5 s s dB % ppm/C ppm 0.01 TA = -40C to +85C VOUT = 20 V p-p VS = 15 V, RL = 10 k, TA = -40C to +85C 0.05 5 10 -VS + 0.2 15 200 +VS - 0.2 -VS + 0.2 15 200 2 65 +VS - 0.2 V mA pF V p-p nV/Hz A A V C f = 0.1 Hz to 10 Hz f = 1 kHz 2 65 70 200 250 18 +125 70 200 250 18 +125 TA = -40C to +85C 2 -40 2 -40 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 18 through Figure 21 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 22 and Figure 24 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. Rev. A | Page 3 of 20 AD8276/AD8277 VS = +2.7 V to <5 V, VREF = midsupply, TA = 25C, RL = 10 k connected to midsupply, G = 1 difference amplifier configuration, unless otherwise noted. Table 3. G=1 Parameter INPUT CHARACTERISTICS System Offset 1 vs. Temperature Average Temperature Coefficient vs. Power Supply Common-Mode Rejection Ratio (RTI) Conditions Min Grade B Typ 100 TA = -40C to +85C TA = -40C to +85C VS = 5 V to 18 V VS = 2.7 V, VCM = 0 V to 2.4 V, RS = 0 VS = 5 V, VCM = -10 V to +7 V, RS = 0 0.5 Max 200 200 2 5 80 80 -2(VS + 0.1) 80 40 450 1.0 5 130 0.02 1 0.01 0.05 5 Min Grade A Typ Max 100 500 500 5 10 Unit V V V/C V/V dB dB V k k kHz V/s s dB % ppm/C 2 86 86 -2(VS + 0.1) 80 40 450 1.0 Input Voltage Range 2 Impedance 3 Differential Common Mode DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% Channel Separation 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 1 2 +2(VS - 1.5) +2(VS - 1.5) 8 V step on output, CL = 100 pF, VS = 10 V f = 1 kHz 5 130 0.005 TA = -40C to +85C RL = 10 k , TA = -40C to +85C -VS + 0.1 10 200 +VS - 0.15 -VS + 0.1 10 200 2 65 +VS - 0.15 V mA pF V p-p nV/Hz f = 0.1 Hz to 10 Hz f = 1 kHz TA = -40C to +85C 2.0 2 65 200 36 2.0 200 36 A V -40 +125 -40 +125 C 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 18 through Figure 21 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 23 and Figure 24 for details. Rev. A | Page 4 of 20 AD8276/AD8277 ABSOLUTE MAXIMUM RATINGS 2.0 Table 4. 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) Rating 18 V -VS + 40 V +VS - 40 V -65C to +150C -40C to +85C 150C MAXIMUM POWER DISSIPATION (W) 1.6 14-LEAD SOIC JA = 105C/W TJ MAX = 150C 1.2 8-LEAD SOIC JA = 121C/W 0.8 8-LEAD MSOP JA = 135C/W 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. 0.4 -25 0 25 50 75 100 125 AMBIENT TEMERATURE (C) Figure 3. Maximum Power Dissipation vs. Ambient Temperature SHORT-CIRCUIT CURRENT The AD8276/AD8277 have built-in, short-circuit protection that limits the output current (see Figure 25 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 3 and Figure 25, 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. THERMAL RESISTANCE The JA values in Table 5 assume a 4-layer JEDEC standard board with zero airflow. Table 5. Package Type 8-Lead MSOP 8-Lead SOIC 14-Lead SOIC JA 135 121 105 Unit C/W C/W C/W ESD CAUTION MAXIMUM POWER DISSIPATION The maximum safe power dissipation for the AD8276/AD8277 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150C, 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 150C for an extended period may result in a loss of functionality. Rev. A | Page 5 of 20 07692-002 0 -50 AD8276/AD8277 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS REF 1 -IN 2 +IN 3 -VS 4 8 AD8276 TOP VIEW (Not to Scale) NC +VS OUT 07692-003 REF 1 -IN 2 7 6 5 AD8276 8 7 6 5 NC +VS OUT 07692-004 SENSE TOP VIEW +IN 3 (Not to Scale) -VS 4 SENSE NC = NO CONNECT NC = NO CONNECT Figure 4. AD8276 8-Lead MSOP Pin Configuration Figure 5. AD8276 8-Lead SOIC Pin Configuration Table 6. AD8276 Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 Mnemonic REF -IN +IN -VS SENSE OUT +VS NC Description Reference Voltage Input. Inverting Input. Noninverting Input. Negative Supply. Sense Terminal. Output. Positive Supply. No Connect. Rev. A | Page 6 of 20 AD8276/AD8277 NC 1 -INA 2 +INA 3 -VS 4 14 REFA 13 OUTA AD8277 12 SENSEA TOP VIEW 11 +VS (Not to Scale) +INB 5 10 SENSEB -INB 6 NC 7 9 8 OUTB 07692-053 REFB NC = NO CONNECT Figure 6. AD8277 14-Lead SOIC Pin Configuration Table 7. AD8277 Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Mnemonic NC -INA +INA -VS +INB -INB NC REFB OUTB SENSEB +VS SENSEA OUTA REFA Description No Connect. Channel A Inverting Input. Channel A Noninverting Input. Negative Supply. Channel B Noninverting Input. Channel B Inverting Input. No Connect. Channel B Reference Voltage Input. Channel B Output. Channel B Sense Terminal. Positive Supply. Channel A Sense Terminal. Channel A Output. Channel A Reference Voltage Input. Rev. A | Page 7 of 20 AD8276/AD8277 TYPICAL PERFORMANCE CHARACTERISTICS VS = 15 V, TA = 25C, RL = 10 k connected to ground, G = 1 difference amplifier configuration, unless otherwise noted. 600 500 SYSTEM OFFSET (V) NUMBER OF HITS N = 2042 MEAN = -2.28 SD = 32.7 80 60 40 20 0 -20 -40 -60 400 300 200 100 -80 07692-008 07692-010 07692-009 -200 -100 0 100 200 300 07692-005 0 -300 SYSTEM OFFSET VOLTAGE (V) -100 -50 -35 -20 -5 10 25 40 55 70 85 TEMPERATURE (C) Figure 7. Distribution of Typical System Offset Voltage N = 2040 MEAN = -0.87 SD = 16.2 Figure 10. System Offset vs. Temperature, Normalized at 25C 20 15 10 400 NUMBER OF HITS GAIN ERROR (V/V) 300 5 0 -5 -10 -15 -20 -25 REPRESENTATIVE DATA -30 -50 -35 -20 -5 10 200 100 -60 -30 0 CMRR (V/V) 30 60 90 07692-006 0 -90 25 40 55 70 85 90 TEMPERATURE (C) Figure 8. Distribution of Typical Common-Mode Rejection 4 Figure 11. Gain Error vs. Temperature, Normalized at 25C 10 2 0 VS = 15V -10 GAIN (dB) 0 CMRR (V/V) -2 -20 VS = +2.7V -4 -30 -6 REPRESENTATIVE DATA -8 -50 -35 -20 -5 10 -40 07692-007 25 40 55 70 85 90 -50 100 1k 10k 100k 1M 10M TEMPERATURE (C) FREQUENCY (Hz) Figure 9. CMRR vs. Temperature, Normalized at 25C Figure 12. Gain vs. Frequency, VS = 15 V, +2.7 V Rev. A | Page 8 of 20 AD8276/AD8277 120 VS = 15V 8 6 COMMON-MODE VOLTAGE (V) VREF = MIDSUPPLY 100 VS = 5V 4 2 0 -2 -4 -6 -0.5 VS = 2.7V 80 CMRR (dB) 60 40 20 07692-011 1 10 100 1k 10k 100k 1M 0.5 1.5 2.5 3.5 4.5 5.5 FREQUENCY (Hz) OUTPUT VOLTAGE (V) Figure 13. CMRR vs. Frequency Figure 16. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = Midsupply 8 VS = 5V VREF = 0V 120 80 PSRR (dB) COMMON-MODE VOLTAGE (V) 100 6 4 -PSRR 60 +PSRR 40 2 VS = 2.7V 0 20 -2 07692-012 1 10 100 1k 10k 100k 1M 0.5 1.5 2.5 3.5 4.5 5.5 FREQUENCY (Hz) OUTPUT VOLTAGE (V) Figure 14. PSRR vs. Frequency 30 VS = 15V COMMON-MODE VOLTAGE (V) Figure 17. Input Common-Mode Voltage vs. Output Voltage, 5 V and 2.7 V Supplies, VREF = 0 V +VS -0.1 20 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES -0.2 -0.3 -0.4 TA = -40C TA = +25C TA = +85C TA = +125C 10 0 VS = 5V -10 +0.4 +0.3 +0.2 +0.1 -20 07692-013 -15 -10 -5 0 5 10 15 20 2 4 6 8 10 12 14 16 18 OUTPUT VOLTAGE (V) SUPPLY VOLTAGE (VS) Figure 15. Input Common-Mode Voltage vs. Output Voltage, 15 V and 5 V Supplies Figure 18. Output Voltage Swing vs. Supply Voltage Per Channel and Temperature, RL = 10 k Rev. A | Page 9 of 20 07692-016 -30 -20 -VS 07692-015 0 -4 -0.5 07692-014 0 AD8276/AD8277 +VS -0.2 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES 180 -0.4 -0.6 SUPPLY CURRENT (A) 170 -0.8 -1.0 -1.2 TA = -40C TA = +25C TA = +85C TA = +125C 160 150 +1.2 +1.0 +0.8 +0.6 +0.4 +0.2 -VS 140 130 07692-017 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18 SUPPLY VOLTAGE (VS) SUPPLY VOLTAGE (V) Figure 19. Output Voltage Swing vs. Supply Voltage Per Channel and Temperature, RL = 2 k +VS Figure 22. Supply Current Per Channel vs. Dual Supply Voltage, VIN = 0 V 180 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES -4 SUPPLY CURRENT (A) 170 -8 TA = -40C TA = +25C TA = +85C TA = +125C +8 160 150 140 +4 130 07692-018 10k LOAD RESISTANCE () 100k 0 5 10 15 20 25 30 35 40 SUPPLY VOLTAGE (V) Figure 20. Output Voltage Swing vs. RL and Temperature, VS = 15 V +VS -0.5 OUTPUT VOLTAGE SWING (V) REFERRED TO SUPPLY VOLTAGES Figure 23. Supply Current Per Channel vs. Single-Supply Voltage, VIN = 0 V, VREF = 0 V 250 VREF = MIDSUPPLY -1.0 -1.5 -2.0 TA = -40C TA = +25C TA = +85C TA = +125C SUPPLY CURRENT (A) 200 150 VS = 15V 100 VS = +2.7V 50 +2.0 +1.5 +1.0 +0.5 07692-019 0 1 2 3 4 5 6 7 8 9 10 -30 -10 10 30 50 70 90 110 130 OUTPUT CURRENT (mA) TEMPERATURE (C) Figure 21. Output Voltage Swing vs. IOUT and Temperature, VS = 15 V Figure 24. Supply Current Per Channel vs. Temperature Rev. A | Page 10 of 20 07692-022 -VS 0 -50 07692-021 -VS 1k 120 07692-020 120 AD8276/AD8277 30 25 SHORT-CIRCUIT CURRENT (mA) 20 15 10 5 0 -5 -10 -15 -30 -10 10 30 50 70 90 110 130 07692-023 ISHORT+ 5V/DIV 11.24 s TO 0.01% 13.84s TO 0.001% 0.002%/DIV ISHORT- 07692-026 40s/DIV TIME (s) -20 -50 TEMPERATURE (C) Figure 25. Short-Circuit Current Per Channel vs. Temperature 1.4 1.2 1.0 SLEW RATE (V/s) Figure 28. Large-Signal Pulse Response and Settling Time, 10 V Step, VS = 15 V -SR +SR 1V/DIV 4.34 s TO 0.01% 5.12s TO 0.001% 0.8 0.6 0.4 0.2 0 -50 0.002%/DIV -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) Figure 26. Slew Rate vs. Temperature, VIN = 20 V p-p, 1 kHz 8 6 NONLINEARITY (2ppm/DIV) 07692-024 TIME (s) Figure 29. Large-Signal Pulse Response and Settling Time, 2 V Step, VS = 2.7 V 4 2 0 -2 -4 -6 -8 -10 07692-028 2V/DIV -8 -6 -4 -2 0 2 4 6 8 10 OUTPUT VOLTAGE (V) Figure 27. Gain Nonlinearity, VS = 15 V, RL 2 k 07692-025 10s/DIV Figure 30. Large-Signal Step Response Rev. A | Page 11 of 20 07692-027 40s/DIV AD8276/AD8277 30 VS = 15V 25 OUTPUT VOLTAGE (V p-p) 40 35 30 OVERSHOOT (%) 2V 5V 20 25 20 15 10 15V 18V 15 VS = 5V 10 5 5 0 100 07692-029 1k 10k FREQUENCY (Hz) 100k 1M 150 200 250 300 350 400 CAPACITIVE LOAD (pF) Figure 31. Maximum Output Voltage vs. Frequency, VS = 15 V, 5 V 5.0 4.5 4.0 OUTPUT VOLTAGE (V p-p) Figure 34. Small-Signal Overshoot vs. Capacitive Load, RL 2 k 1k VS = 5V 3.5 3.0 2.5 2.0 1.5 1.0 0.5 07692-030 NOISE (nV/ Hz) VS = 2.7V 100 1k 10k FREQUENCY (Hz) 100k 1M 1 10 100 FREQUENCY (Hz) 1k 10k 100k Figure 32. Maximum Output Voltage vs. Frequency, VS = 5 V, 2.7 V Figure 35. Voltage Noise Density vs. Frequency 20mV/DIV CL = 100pF CL = 200pF CL = 300pF 07692-050 07692-035 CL = 470pF 40s/DIV 1V/DIV 1s/DIV Figure 33. Small-Signal Step Response for Various Capacitive Loads Figure 36. 0.1 Hz to 10 Hz Voltage Noise Rev. A | Page 12 of 20 07692-034 0 100 10 0.1 07692-051 0 100 AD8276/AD8277 160 140 CHANNEL SEPARATION (dB) NO LOAD 10k LOAD 120 100 80 60 40 20 0 2k LOAD 1k LOAD 1 10 100 1k 10k 100k FREQUENCY (Hz) Figure 37. Channel Separation Rev. A | Page 13 of 20 07692-055 AD8276/AD8277 THEORY OF OPERATION CIRCUIT INFORMATION Each channel of the AD8276/AD8277 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 AD8276/AD8277 provides the designer with several benefits over a discrete design, including smaller size, lower cost, and better ac and dc performance. +VS 7 AC 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 AD8276/ AD8277. For example, the positive and negative input terminals of the AD8276/AD8277 op amps are intentionally not pinned out. By not connecting these nodes to the traces on the PCB, the capacitance remains low, resulting in improved loop stability and excellent common-mode rejection over frequency. DRIVING THE AD8276/AD8277 AD8276 40k 5 IN- 2 40k SENSE 6 OUT IN+ 3 40k 40k 1 REF 07692-031 4 Care should be taken to drive the AD8276/AD8277 with a low impedance source: for example, another amplifier. Source resistance of even a few kilohms (k) can unbalance the resistor ratios and, therefore, significantly degrade the gain accuracy and common-mode rejection of the AD8276/AD8277. Because all configurations present several kilohms of input resistance, the AD8276/AD8277 do not require a high current drive from the source and so are easy to drive. -VS INPUT VOLTAGE RANGE The AD8276/AD8277 are 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 39 shows an example of how the voltage division works in a difference amplifier configuration. For the AD8276/AD8277 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+ R4 VIN- VIN+ R3 R1 R2 R2 (V ) R1 + R2 IN+ 07692-033 Figure 38. 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 39, the output voltage is found to be R2 1 + R4 - V IN - R4 VOUT = V IN + R1 + R2 R3 R3 This equation demonstrates that the gain accuracy and commonmode rejection ratio of the AD8276/AD8277 is determined primarily by the matching of resistor ratios. Even a 0.1% mismatch in one resistor degrades the CMRR to 66 dB for a G = 1 difference amplifier. The difference amplifier output voltage equation can be reduced to VOUT R4 (VIN + - VI N - ) = R3 as long as the following ratio of the resistors is tightly matched: R2 R4 = R1 R3 Figure 39. Voltage Division in the Difference Amplifier Configuration The resistors on the AD8276/AD8277 are laser trimmed to match accurately. As a result, the AD8276/AD8277 provide superior performance over a discrete solution, enabling better CMRR, gain accuracy, and gain drift, even over a wide temperature range. The AD8276/AD8277 have 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. A | Page 14 of 20 AD8276/AD8277 POWER SUPPLIES The AD8276/AD8277 operate extremely well over a very wide range of supply voltages. They 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 AD8276/AD8277 are typically specified at single- and dualsupplies, but they 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 R1 (V ) R1 + R2 REF 07692-032 R1 V REF < + VS - 1.5 V R1 + R2 For example, when operating on a +VS = 2 V single supply and VREF = 0 V, it can be seen from Figure 40 that the input terminals of the op amp 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 0.5 V, barely allowing the required 1.5 V headroom. This setup does not allow any practical voltage swing on the non inverting input. Therefore, the user needs to increase the supply voltage or decrease VREF to restore proper operation. VREF Figure 40. Ensure Sufficient Voltage Headroom on the Internal Op Amp Inputs Use a stable dc voltage to power the AD8276/AD8277. Noise on the supply pins can adversely affect performance. Place a bypass capacitor of 0.1 F between each supply pin and ground, as close as possible to each supply pin. Use a tantalum capacitor of 10 F 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. A | Page 15 of 20 AD8276/AD8277 APPLICATIONS INFORMATION CONFIGURATIONS The AD8276/AD8277 can be configured in several ways (see Figure 42 to Figure 46). All of these configurations have excellent gain accuracy and gain drift because they rely on the internal matched resistors. Note that Figure 43 shows the AD8276/AD8277 as difference amplifiers with a midsupply reference voltage at the noninverting input. This allows the AD8276/AD8277 to be used as a level shifter, which is appropriate in single-supply applications that are referenced to midsupply. 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 41. INCORRECT CORRECT IN IN 2 40k 40k 5 6 OUT 1 40k 3 40k 07692-040 VOUT = -VIN Figure 44. Inverting Amplifier, Gain = -1 2 40k 40k 5 6 OUT 3 40k 40k 1 07692-041 VOUT = VIN AD8276 REF V + V AD8276 REF Figure 45. Noninverting Amplifier, Gain = 1 2 40k 40k 5 6 OUT OP1177 07692-037 - 1 40k IN 3 40k 07692-042 Figure 41. Driving the Reference Pin VOUT = 2VIN 2 40k 40k Figure 46. Noninverting Amplifier, Gain = 2 -IN 5 6 OUT DIFFERENTIAL OUTPUT Certain systems require a differential signal for better performance, such as the inputs to differential analog-to-digital converters. Figure 47 shows how the AD8276/AD8277 can be used to convert a single-ended output from an AD8226 instrumentation amplifier into a differential signal. The internal matched resistors of the AD8276 at the inverting input maximize gain accuracy while generating a differential signal. The resistors at the noninverting input can be used as a divider to set and track the common-mode voltage accurately to midsupply, especially when running on a single supply or in an environment where the supply fluctuates. The resistors at the noninverting input can also be shorted and set to any appropriate bias voltage. Note that the VBIAS = VCM node indicated in Figure 47 is internal to the AD8276 because it is not pinned out. +IN -IN +IN 3 40k 40k 1 07692-038 VOUT = VIN+ - VIN- Figure 42. Difference Amplifier, Gain = 1 -IN 2 40k 40k 5 6 OUT +IN 3 40k 40k 1 VREF = MIDSUPPLY 07692-039 VOUT = VIN+ - VIN- Figure 43. Difference Amplifier, Gain = 1, Referenced to Midsupply AD8226 VREF VS + +OUT R R AD8276 R R VBIAS = VCM VS- -OUT Figure 47. Differential Output With Supply Tracking on Common-Mode Voltage Reference Rev. A | Page 16 of 20 07692-043 AD8276/AD8277 The differential output voltage and common-mode voltage of the AD8226 is shown in the following equations: VDIFF_OUT = V+OUT - V-OUT = GainAD8226 x (V+IN - V-IN) VCM = (VS+ - VS-)/2 = VBIAS V+ V+ 1 2 3 4 5 V- REF 10 9 8 7 6 2 40k 3 40k 40k 6 2N3904 R1 RLOAD IO = 2.5V(1/40k + 1/R1) R1 = R2 07692-046 -2.5V 7 40k 5 R2 Refer to the AD8226 data sheet for additional information. +VS 11 ADR821 1 AD8276 4 AD8277 -IN 2 40k 40k 12 Figure 49. Constant Current Source 13 +OUT VOLTAGE AND CURRENT MONITORING Voltage and current monitoring is critical in the following applications: power line metering, power line protection, motor control applications, and battery monitoring. The AD8276/ AD8277 can be used to monitor voltages and currents in a system, as shown in Figure 50. As the signals monitored by the AD8276/AD8277 rise above or drop below critical levels, a circuit event can be triggered to correct the situation or raise a warning. AD8276 +IN 3 40k 40k 14 6 40k 40k 10 9 -OUT 5 40k 40k 8 07692-056 4 I1 R -VS Figure 48. AD8277 Differential Output Configuration The two difference amplifiers of the AD8277 can be configured to provide a differential output, as shown in Figure 48. This differential output configuration is suitable for various applications, such as strain gage excitation and single-ended-to-differential conversion. The differential output voltage has a gain of 2 as shown in the following equation: VDIFF_OUT = V+OUT - V-OUT = 2 x (V+IN - V-IN) AD8276 I3 IC R AD8276 V1 R 8:1 OP1177 ADC AD8276 V3 R CURRENT SOURCE The AD8276 difference amplifier can be implemented as part of a voltage-to-current converter or a precision constant current source as shown in Figure 49. Using an integrated precision solution such as the AD8276 provides several advantages over a discrete solution, including space-saving, improved gain accuracy, and temperature drift. The internal resistors are tightly matched to minimize error and temperature drift. If the external resistors, R1 and R2, are not well-matched, they become a significant source of error in the system, so precision resistors are recommended to maintain performance. The ADR821 provides a precision voltage reference and integrated op amp that also reduces error in the signal chain. The AD8276 has rail-to-rail output capability that allows higher current outputs. AD8276 VC R 07692-057 Figure 50.Voltage and Current Monitoring in 3-Phase Power Line Protection Using the AD8276 Figure 50 shows an example of how the AD8276 can be used to monitor voltage and current on a 3-phase power supply. I1 through I3 are the currents to be monitored, and V1 through V3 are the voltages to be monitored on each phase. IC and VC are the common or zero lines. Couplers or transformers interface the power lines to the front-end circuitry and provide attenuation, isolation, and protection. On the current monitoring side, current transformers (CTs) step down the power-line current and isolate the front-end circuitry from the high voltage and high current lines. Across the inputs of each difference amplifier is a shunt resistor that converts the coupled current into a voltage. The value of the Rev. A | Page 17 of 20 AD8276/AD8277 resistor is determined by the characteristics of the coupler or transformer and desired input voltage ranges to the AD8276. On the voltage monitoring side, potential transformers (PTs) are used to provide coupling and galvanic isolation. The PTs present a load to the power line and also step down the voltage to a measureable level. The AD8276 helps to build a robust system because it allows input voltages that are almost double its supply voltage, while providing additional input protection in the form of the integrated ESD diodes. Not only does the AD8276 monitor the voltage and currents on the power lines, it is able to reject very high common-mode voltages that may appear at the inputs. The AD8276 also performs the differential-to-single-ended conversion on the input voltages. The 80 k differential input impedance that the AD8276 presents is high enough that it should not load the input signals. ISH RSH Table 8. Low Power Op Amps Op Amp (A1, A2) AD8506 AD8607 AD8617 AD8667 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 AD8276 difference amplifiers cancel out common-mode errors from the input op amps, if they track each other. The differential gain accuracy of the inamp 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. AD8276 VOUT = ISH x RSH 07692-058 RTD Resistive temperature detectors (RTDs) are often measured remotely in industrial control systems. The wire lengths needed to connect the RTD to a controller add significant cost and resistance errors to the measurement. The AD8276 difference amplifier is effective in measuring errors caused by wire resistance in remote 3-wire RTD systems, allowing the user to cancel out the errors introduced by the wires. Its excellent gain drift provides accurate measurements and stable performance over a wide temperature range. IEX RL1 Figure 51. AD8276 Monitoring Current Through a Shunt Resistor Figure 51 shows how the AD8276 can be used to monitor the current through a small shunt resistor. This is useful in power critical applications such as motor control (current sense) and battery monitoring. INSTRUMENTATION AMPLIFIER The AD8276/AD8277 can be used as building blocks for a low power, low cost instrumentation amplifier. An instrumentation amplifier provides high impedance inputs and delivers high common-mode rejection. Combining the AD8276 with an Analog Devices, Inc. low power amplifier (see Table 8) creates a precise, power efficient voltage measurement solution suitable for power critical systems. -IN A1 RF 40k RG 40k RF A2 +IN 40k REF VOUT = (1 + 2RF/RG) (VIN+ - VIN-) VOUT 40k RT RL2 VOUT - ADC REF Figure 53. 3-Wire RTD Cable Resistance Error Measurement AD8276 07692-045 Figure 52. Low Power Precision Instrumentation Amplifier Rev. A | Page 18 of 20 07692-059 RL3 AD8276 AD8276/AD8277 OUTLINE DIMENSIONS 3.20 3.00 2.80 3.20 3.00 2.80 PIN 1 8 5 1 5.15 4.90 4.65 4 0.65 BSC 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 MAX 8 0 0.80 0.60 0.40 0.23 0.08 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 54. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 8 1 5 4 6.20 (0.2441) 5.80 (0.2284) 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 1.75 (0.0688) 1.35 (0.0532) 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) 45 0.51 (0.0201) 0.31 (0.0122) 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 55. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) Rev. A | Page 19 of 20 012407-A AD8276/AD8277 Figure 56. 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches) ORDERING GUIDE Model AD8276ARZ 1 AD8276ARZ-R71 AD8276ARZ-RL1 AD8276BRZ1 AD8276BRZ-R71 AD8276BRZ-RL1 AD8276ARMZ1 AD8276ARMZ-R71 AD8276ARMZ-RL1 AD8276BRMZ1 AD8276BRMZ-R71 AD8276BRMZ-RL1 AD8277ARZ1 AD8277ARZ-R71 AD8277ARZ-RL1 AD8277BRZ1 AD8277BRZ-R71 AD8277BRZ-RL1 1 Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C 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 14-Lead SOIC_N 14-Lead SOIC_N, 7" Tape and Reel 14-Lead SOIC_N, 13" Tape and Reel 14-Lead SOIC_N 14-Lead SOIC_N, 7" Tape and Reel 14-Lead SOIC_N, 7" Tape and Reel 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 R-14 R-14 R-14 R-14 R-14 R-14 Branding H1P H1P H1P H1Q H1Q H1Q Z = RoHS Compliant Part. (c)2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07692-0-7/09(A) Rev. A | Page 20 of 20 |
Price & Availability of AD8276ARZ-R7
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |