 |
|
| 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: |
| Precision Dual-Channel, Difference Amplifier AD8270 FEATURES With no external resistors Difference amplifier: gains of 0.5, 1, or 2 Single ended amplifiers: over 40 different gains Set reference voltage at midsupply Excellent ac specifications 15 MHz bandwidth 30 V/s slew rate High accuracy dc performance 0.08% maximum gain error 10 ppm/C maximum gain drift 80 dB minimum CMRR (G = 2) Two channels in small 4 mm x 4 mm LFCSP Supply current: 2.5 mA per channel Supply range: 2.5 V to 18 V FUNCTIONAL BLOCK DIAGRAM 16 +VS 15 OUTA 14 OUTB 13 -VS -IN1A 1 -IN2A 2 +IN2A 3 +IN1A 4 10k 10k 10k 10k 10k 10k 10k 12 -IN1B 11 -IN2B 10 +IN2B 9 +IN1B _ + _ + 10k 10k 10k AD8270 20k 20k REF2A 6 20k REF2B 7 20k REF1B 8 Instrumentation amplifier building blocks Level translators Automatic test equipment High performance audio Sine/Cosine encoders Figure 1. GENERAL DESCRIPTION The AD8270 is a low distortion, dual-channel amplifier with internal gain setting resistors. With no external components, it can be configured as a high performance difference amplifier with gains of 0.5, 1, or 2. It can also be configured in over 40 singleended configurations, with gains ranging from -2 to +3. The AD8270 is the first dual-difference amplifier in the small 4 mm x 4 mm LFCSP. It requires the same board area as a typical single-difference amplifier. The smaller package allows a 2x increase in channel density and a lower cost per channel, all with no compromise in performance. The AD8270 operates on both single and dual supplies and requires only 2.5 mA maximum supply current for each amplifier. It is specified over the industrial temperature range of -40C to +85C and is fully RoHS compliant. Table 1. Difference Amplifiers by Category High Speed AD8270 AD8273 AMP03 High Voltage AD628 AD629 Single-Supply Unidirectional AD8202 AD8203 Single-Supply Bidirectional AD8205 AD8206 AD8216 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 (c)2008 Analog Devices, Inc. All rights reserved. 06979-001 APPLICATIONS REF1A 5 AD8270 TABLE OF CONTENTS Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Difference Amplifier Configurations ........................................ 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...................................................................... 5 Maximum Power Dissipation ..................................................... 5 ESD Caution.................................................................................. 5 Pin Configuration and Function Descriptions............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 13 Circuit Information.................................................................... 13 Driving the AD8270................................................................... 13 Package Considerations............................................................. 13 Power Supplies............................................................................ 13 Input Voltage Range................................................................... 14 Applications Information .............................................................. 15 Difference Amplifier Configurations ...................................... 15 Single-Ended Configurations ................................................... 15 Differential Output .................................................................... 17 Driving an ADC ......................................................................... 18 Driving Cabling .......................................................................... 18 Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 19 REVISION HISTORY 1/08--Revision 0: Initial Version Rev. 0 | Page 2 of 20 AD8270 SPECIFICATIONS DIFFERENCE AMPLIFIER CONFIGURATIONS VS = 15 V, VREF = 0 V, TA = 25C, RLOAD = 2 k, specifications referred to input, unless otherwise noted. Table 2. Parameter DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% Settling Time to 0.001% NOISE/DISTORTION Harmonic Distortion Voltage Noise 1 GAIN Gain Error Gain Drift INPUT CHARACTERISTICS Offset 2 Average Temperature Drift Common-Mode Rejection Ratio Power Supply Rejection Ratio Input Voltage Range 3 Common-Mode Resistance 4 Bias Current OUTPUT CHARACTERISTICS Output Swing Short-Circuit Current Limit POWER SUPPLY Supply Current (per Amplifier) TA = -40C to +85C 1 2 3 Conditions Min G = 0.5 Typ Max 20 30 700 750 84 2 52 0.08 10 1500 Min G=1 Typ Max 15 30 700 750 145 1.5 38 0.08 10 1000 Min G=2 Typ Max 10 30 700 750 95 1 26 0.08 10 750 Unit MHz V/s ns ns dB V p-p nV/Hz % ppm/C V V/C dB V/V V k nA V V mA mA mA mA 10 V step on output 10 V step on output f = 1 kHz, VOUT = 10 V p-p, RLOAD = 600 f = 0.1 Hz to 10 Hz f = 1 kHz 800 900 800 900 800 900 TA = -40C to +85C 1 450 3 86 2 -15.4 7.5 1 300 2 92 2 -15.4 10 1 225 1.5 98 2 -15.4 7.5 TA = -40C to +85C DC to 1 kHz 70 76 10 +15.4 500 80 10 +15.4 500 10 +15.4 500 TA = -40C to +85C Sourcing Sinking -13.8 -13.7 100 60 2.3 +13.8 +13.7 -13.8 -13.7 100 60 +13.8 +13.7 -13.8 -13.7 100 60 +13.8 +13.7 2.5 3 2.3 2.5 3 2.3 2.5 3 Includes amplifier voltage and current noise, as well as noise of internal resistors. Includes input bias and offset errors. At voltages beyond the rails, internal ESD diodes begin to turn on. In some configurations, the input voltage range may be limited by the internal op amp (see the Input Voltage Range section for details). 4 Internal resistors are trimmed to be ratio matched but have 20% absolute accuracy. Common-mode resistance was calculated with both inputs in parallel. Commonmode impedance at only one input is 2x the resistance listed. Rev. 0 | Page 3 of 20 AD8270 VS = 5 V, VREF = 0 V, TA = 25C, RLOAD = 2 k, specifications referred to input, unless otherwise noted. Table 3. Parameter DYNAMIC PERFORMANCE Bandwidth Slew Rate Settling Time to 0.01% Settling Time to 0.001% NOISE/DISTORTION Harmonic Distortion Voltage Noise 1 GAIN Gain Error Gain Drift INPUT CHARACTERISTICS Offset 2 Average Temperature Drift Common-Mode Rejection Ratio Power Supply Rejection Ratio Input Voltage Range 3 Common-Mode Resistance 4 Bias Current OUTPUT CHARACTERISTICS Output Swing Short-Circuit Current Limit POWER SUPPLY Supply Current (per Amplifier) TA = -40C to +85C 1 2 3 Conditions Min G = 0.5 Typ Max 20 30 550 600 101 2 52 0.08 10 1500 Min G=1 Typ Max 15 30 550 600 141 1.5 38 0.08 10 1000 Min G=2 Typ Max 10 30 550 600 112 1 26 0.08 10 750 Unit MHz V/s ns ns dB V p-p nV/Hz % ppm/C V V/C dB dB V k nA V V mA mA mA mA 5 V step on output 5 V step on output f = 1 kHz, VOUT = 5 V p-p, RLOAD = 600 f = 0.1 Hz to 10 Hz f = 1 kHz 650 750 650 750 650 750 TA = -40C to +85C 1 450 3 86 2 -5.4 7.5 1 300 2 92 2 -5.4 10 1 225 1.5 98 2 -5.4 7.5 TA = -40C to +85C DC to 1 kHz 70 76 10 +5.4 500 80 10 +5.4 500 10 +5.4 500 TA = -40C to +85C Sourcing Sinking -4 -3.9 100 60 2.3 +4 +3.9 -4 -3.9 100 60 +4 +3.9 -4 -3.9 100 60 +4 +3.9 2.5 3 2.3 2.5 3 2.3 2.5 3 Includes amplifier voltage and current noise, as well as noise of internal resistors. Includes input bias and offset errors. At voltages beyond the rails, internal ESD diodes begin to turn on. In some configurations, the input voltage range may be limited by the internal op amp (see the Input Voltage Range section for details). 4 Internal resistors are trimmed to be ratio matched but have 20% absolute accuracy. Common-mode resistance was calculated with both inputs in parallel. Commonmode impedance at only one input is 2x the resistance listed. Rev. 0 | Page 4 of 20 AD8270 ABSOLUTE MAXIMUM RATINGS Table 4. Parameter Supply Voltage Output Short-Circuit Current Input Voltage Range Storage Temperature Range Specified Temperature Range Package Glass Transition Temperature (TG) ESD (Human Body Model) ESD (Charge Device Model) ESD (Machine Model) Rating 18 V See derating curve in Figure 2 VS -65C to +130C -40C to +85C 130C 1 kV 1 kV 0.1 kV MAXIMUM POWER DISSIPATION The maximum safe power dissipation for the AD8270 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 130C, which is the glass transition temperature, the plastic changes its properties. 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 130C for an extended period of time can result in a loss of functionality. The AD8270 has built-in, short-circuit protection that limits the output current to approximately 100 mA (see Figure 19 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. 3.2 TJ MAXIMUM = 130C 2.8 2.4 2.0 1.6 1.2 0.8 0.4 06979-003 MAXIMUM POWER DISSIPATION (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. PAD SOLDERED JA = 57C/W THERMAL RESISTANCE Table 5. Thermal Resistance Thermal Pad 16-Lead LFCSP with Thermal Pad Soldered to Board 16-Lead LFCSP with Thermal Pad Not Soldered to Board JA 57 96 Unit C/W C/W PAD NOT SOLDERED JA = 96C/W 0 -50 -25 The JA values in Table 5 assume a 4-layer JEDEC standard board with zero airflow. If the thermal pad is soldered to the board, it is also assumed it is connected to a plane. JC at the exposed pad is 9.7C/W. 0 25 50 75 AMBIENT TEMPERATURE (C) 100 125 Figure 2. Maximum Power Dissipation vs. Ambient Temperature ESD CAUTION Rev. 0 | Page 5 of 20 AD8270 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 16 +VS 15 OUTA 14 OUTB 13 -VS 12 -IN1B 11 -IN2B 10 +IN2B 9 +IN1B -IN1A 1 -IN2A 2 +IN2A 3 +IN1A 4 PIN 1 INDICATOR TOP VIEW (Not to Scale) AD8270 REF1B 8 REF2B 7 REF1A 5 REF2A 6 Figure 3. Pin Configuration Table 6. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic -IN1A -IN2A +IN2A +IN1A REF1A REF2A REF2B REF1B +IN1B +IN2B -IN2B -IN1B -VS OUTB OUTA +VS Description 10 k Resistor Connected to Negative Terminal of Op Amp A. 10 k Resistor Connected to Negative Terminal of Op Amp A. 10 k Resistor Connected to Positive Terminal of Op Amp A. 10 k Resistor Connected to Positive Terminal of Op Amp A. 20 k Resistor Connected to Positive Terminal of Op Amp A. Most configurations use this pin as a reference voltage input. 20 k Resistor Connected to Positive Terminal of Op Amp A. Most configurations use this pin as a reference voltage input. 20 k Resistor Connected to Positive Terminal of Op Amp B. Most configurations use this pin as a reference voltage input. 20 k Resistor Connected to Positive Terminal of Op Amp B. Most configurations use this pin as a reference voltage input. 10 k Resistor Connected to Positive Terminal of Op Amp B. 10 k Resistor Connected to Positive Terminal of Op Amp B. 10 k Resistor Connected to Negative Terminal of Op Amp B. 10 k Resistor Connected to Negative Terminal of Op Amp B. Negative Supply. Op Amp B Output. Op Amp A Output. Positive Supply. Rev. 0 | Page 6 of 20 06979-002 AD8270 TYPICAL PERFORMANCE CHARACTERISTICS VS = 15 V, TA = 25C, difference amplifier configuration, unless otherwise noted. 160 140 120 NUMBER OF UNITS 20 COMMON-MODE INPUT VOLTAGE (V) N: 1043 MEAN: -0.003 SD: 0.28 (0, +15) 15 10 5 0 -5 -10 -15 (0, -15) 06979-004 (-7.5, +7.5) (+7.5, +7.5) 100 80 60 40 20 0 (-7.5, -7.5) (+7.5, -7.5) -0.9 -0.6 -0.3 0 0.3 0.6 SYSTEM OFFSET VOLTAGE (mV) 0.9 -5 0 OUTPUT VOLTAGE (V) 5 10 Figure 4. Typical Distribution of System Offset Voltage, G = 1 Figure 7. Common-Mode Input Voltage vs. Output Voltage, Gain = 0.5, 15 V Supplies 6 (0, +5) COMMON-MODE INPUT VOLTAGE (V) 180 150 NUMBER OF UNITS N: 984 MEAN: -1.01 SD: 27 4 (-2.5, +2.5) (-1.25, -1.25) (0, +2.5) (+2.5, +2.5) (+1.25, +1.25) 2 120 90 60 30 0 -150 VS = 2.5 0 VS = 5 -2 (-1.25, -1.25) (-2.5, -2.5) (0, -2.5) (+1.25, -1.25) (+2.5, -2.5) -4 06979-005 -100 -50 0 CMRR (V/V) 50 100 150 -2 -1 0 1 OUTPUT VOLTAGE (V) 2 3 Figure 5. Typical Distribution of CMRR, G = 1 Figure 8. Common-Mode Input Voltage vs. Output Voltage, Gain = 0.5, 5 V and 2.5 V Supplies 20 (0, +15) 400 350 300 COMMON-MODE INPUT VOLTAGE (V) N: 1043 MEAN: -0.015 SD: 0.0068 15 10 5 0 -5 -10 -15 (0, -15) 06979-009 (-14.3, +7.85) (+14.3, +7.85) NUMBER OF UNITS 250 200 150 100 50 06979-006 (-14.3, -7.85) (+14.3, -7.85) 0 -0.04 -0.02 0 GAIN ERROR (%) 0.02 0.04 -20 -20 -15 -10 -5 0 5 OUTPUT VOLTAGE (V) 10 15 20 Figure 6. Typical Distribution of Gain Error, G = 1 Figure 9. Common-Mode Input Voltage vs. Output Voltage, Gain = 1, 15 V Supplies Rev. 0 | Page 7 of 20 06979-008 -6 -3 (0, -5) 06979-007 -20 -10 AD8270 6 (0, +5) (+4.3, +2.85) (0, +2.5) 2 (-1.6, +1.7) VS = 2.5 0 (+1.6, +1.7) VS = 5 140 GAIN = 2, 0.5 120 100 80 60 40 20 0 10 COMMON-MODE INPUT VOLTAGE (V) 4 (-4.3, +2.85) -2 (-1.6, -1.7) (0, -2.5) (+1.6, -1.7) -2.85) -4 (-4.3, +2.85) (0, -5) (+4.3, -2.85) 06979-010 -4 -3 -2 -1 0 1 2 OUTPUT VOLTAGE (V) 3 4 5 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 10. Common-Mode Input Voltage vs. Output Voltage, Gain = 1, 5 V and 2.5 V Supplies 20 (0, +15) Figure 13. Positive PSRR vs. Frequency 140 GAIN = 2, 0.5 120 COMMON-MODE INPUT VOLTAGE (V) 15 (-14.3, +11.4) 10 5 0 -5 -10 -15 (0, -15) 06979-011 (+14.3, +11.4) NEGATIVE PSRR (dB) 100 80 60 40 20 0 10 GAIN = 1 (-14.3, -11.4) (+14.3, -11.4) -15 -10 -5 0 5 OUTPUT VOLTAGE (V) 10 15 20 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 11. Common-Mode Input Voltage vs. Output Voltage, Gain = 2, 15 V Supplies 6 32 (0, +5) (-4, +4) 4 (-1.6, +2.1) 2 VS = 2.5 0 VS = 5 (0, +2.5) (+1.6, +2.1) (+4, +4) 28 Figure 14. Negative PSRR vs. Frequency VS = 15V COMMON-MODE INPUT VOLTAGE (V) OUTPUT VOLTAGE SWING (V p-p) 24 20 16 12 8 4 VS = 5V -2 (-1.6, -2.1) -4 (-4, -4) -6 -5 (0, -5) 06979-012 (0, -2.5) (+1.6, -2.1) (+4, -4) -4 -3 -2 -1 0 1 2 OUTPUT VOLTAGE (V) 3 4 5 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 12. Common-Mode Input Voltage vs. Output Voltage, Gain = 2, 5 V and 2.5 V Supplies Figure 15. Output Voltage Swing vs. Large Signal Frequency Response Rev. 0 | Page 8 of 20 06979-017 0 100 06979-016 -20 -20 06979-015 -6 -5 POSITIVE PSRR (dB) GAIN = 1 AD8270 10 GAIN = 2 120 100 SHORT-CIRCUIT CURRENT (mA) 80 60 40 20 0 -20 -40 -60 -80 -100 06979-018 ISHORT+ 5 GAIN = 1 0 GAIN (dB) -5 GAIN = 0.5 -10 ISHORT- -15 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M -20 0 20 40 60 80 100 120 TEMPERATURE (C) Figure 16. Gain vs. Frequency 100 90 80 70 GAIN = 2, 0.5 Figure 19. Short-Circuit Current vs. Temperature +VS +125C OUTPUT VOLTAGE SWING (V) GAIN = 1 +VS - 2 -40C +25C +85C +VS - 4 CMRR (dB) 60 50 40 30 20 10 06979-019 0 +125C +85C +25C -VS + 2 -VS + 4 -40C 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 1k RLOAD () 10k Figure 17. CMRR vs. Frequency 0 CROSSTALK (G = 1) -20 -40 -60 -80 -100 -120 -140 10 Figure 20. Output Voltage Swing vs. RLOAD +VS -40C +25C OUTPUT VOLTAGE SWING (V) +VS - 3 CHANNEL SEPARATION (dB) +VS - 6 +125C +85C 0 +125C +85C +25C -VS + 3 -VS -40C 06979-023 -VS + 6 06979-013 100 1k FREQUENCY (Hz) 10k 100k 0 20 40 60 80 100 CURRENT (mA) Figure 18. Channel Separation vs. Frequency Figure 21. Output Voltage Swing vs. Current (IOUT) Rev. 0 | Page 9 of 20 06979-022 0 10 -VS 200 06979-021 -20 100 -120 -40 AD8270 VS = 15V 100pF 160 140 0pF 18pF 120 OVERSHOOT (%) VS = 2.5V VS = 5V VS = 10V 50mV/DIV 100 80 60 40 20 VS = 15V VS = 18V 06979-024 1s/DIV 0 10 20 30 40 50 60 70 CAPACITIVE LOAD (pF) 80 90 100 Figure 22. Small Signal Step Response, Gain = 0.5 Figure 25. Small Signal Overshoot with Capacitive Load, Gain = 0.5 80 70 60 OVERSHOOT (%) VS = 15V 220pF 0pF 33pF VS = 10V VS = 5V VS = 2.5V 50mV/DIV 50 40 30 20 VS = 18V VS = 15V 10 06979-025 06979-031 06979-032 1s/DIV 0 0 50 100 150 CAPACITIVE LOAD (pF) 200 Figure 23. Small Signal Step Response, Gain = 1 Figure 26. Small Signal Overshoot with Capacitive Load, Gain = 1 80 70 VS = 15V 470pF 0pF 100pF 60 OVERSHOOT (%) 50ms/DIV 50 VS = 10V 40 30 20 10 VS = 18V VS = 15V 0 0 50 100 150 200 250 300 350 CAPACITIVE LOAD (pF) 400 450 VS = 5V VS = 2.5V 1s/DIV Figure 24. Small Signal Step Response, Gain = 2 06979-026 Figure 27. Small Signal Overshoot with Capacitive Load, Gain = 2 Rev. 0 | Page 10 of 20 06979-030 0 AD8270 VS = 15V VIN = 5V 45 40 OUTPUT SLEW RATE (V/s) 35 30 25 20 15 10 5 06979-033 +SR -SR 1V/DIV 1s/DIV Figure 28. Large Signal Pulse Response Gain = 0.5 1k Figure 31. Output Slew Rate vs. Temperature VS = 15V VIN = 5V VOLTAGE NOISE (nV/Hz) GAIN = 2 100 GAIN = 1 2V/DIV 06979-034 GAIN = 0.5 1 10 100 1k FREQUENCY (Hz) 10k 100k 06979-041 1s/DIV 10 Figure 29. Large Signal Pulse Response Gain = 1 Figure 32. Voltage Noise Spectral Density vs. Frequency, Referred to Output VS = 15V VIN = 5V GAIN = 2 GAIN = 1 5V/DIV GAIN = 1/2 1s/DIV Figure 30. Large Signal Pulse Response, Gain = 2 06979-035 1V/DIV 1s/DIV Figure 33. 0.1 Hz to 10 Hz Voltage Noise, Referred to Output Rev. 0 | Page 11 of 20 06979-042 06979-036 0 -45 -35 -25 -15 -5 5 15 25 35 45 55 65 75 85 95 105 115 125 TEMPERATURE (C) AD8270 210 180 N: 1043 MEAN: 4.6 SD: 134.5 NUMBER OF UNITS 150 120 90 60 30 0 06979-014 OFFSET (10V/DIV) -600 -400 -200 0 VOSI (V) 200 400 600 0 1 2 3 4 5 6 TIME (s) 7 8 9 10 Figure 34. Typical Distribution of Op Amp Voltage Offset 100 N: 1043 MEAN: 321.6 SD: 6.9 Figure 37. Change in Op Amp Offset Voltage vs. Warm-Up Time 80 NUMBER OF UNITS 60 40 20 50pA/DIV 1s/DIV 06979-028 310 315 320 325 IBIAS (nA) 330 335 340 06979-020 0 Figure 35. Typical Distribution of Op Amp Bias Current 160 140 N: 1043 MEAN: 0.31 SD: 2.59 Figure 38. 0.1 Hz to 10 Hz Current Noise of Internal Op Amp 10 NUMBER OF UNITS 120 100 80 60 40 20 06979-027 CURRENT NOISE (pA/Hz) 1 -9 -6 -3 0 3 IOFFSET (nA) 6 9 12 1 10 100 1k FREQUENCY (Hz) 10k 100k Figure 36. Typical Distribution of Op Amp Offset Current Figure 39. Current Noise Spectral Density of Internal Op Amp Rev. 0 | Page 12 of 20 06979-029 0 0.1 06979-044 AD8270 THEORY OF OPERATION 15 OUTA 14 OUTB 16 +VS 13 -VS Size The AD8270 fits two op amps and 14 resistors in a 4 mm x 4 mm package. DRIVING THE AD8270 -IN1A 1 -IN2A 2 +IN2A 3 +IN1A 4 10k 10k 10k 10k 10k 10k 10k 12 -IN1B 11 -IN2B 10 +IN2B 9 +IN1B _ + _ + 10k 10k 10k AD8270 The AD8270 is easy to drive, with all configurations presenting at least several kilohms (k) of input resistance. The AD8270 should be driven with a low impedance source: for example, another amplifier. The gain accuracy and common-mode rejection of the AD8270 depend on the matching of its resistors. Even source resistance of a few ohms can have a substantial effect on these specifications. 20k 20k 20k 20k PACKAGE CONSIDERATIONS The AD8270 is packaged in a 4 mm x 4 mm LFCSP. Beware of blindly copying the footprint from another 4 mm x 4 mm LFCSP part; it may not have the same thermal pad size and leads. Refer to the Outline Dimensions section to verify that the PCB symbol has the correct dimensions. The 4 mm x 4 mm LFCSP of the AD8270 comes with a thermal pad. This pad is connected internally to -VS. Connecting to this pad is not necessary for electrical performance; the pad can be left unconnected or can be connected to the negative supply rail. Connecting the pad to the negative supply rail is recommended in high vibration applications or when good heat dissipation is required (for example, with high ambient temperatures or when driving heavy loads). For best heat dissipation performance, the negative supply rail should be a plane in the board. See the Absolute Maximum Ratings section for thermal coefficients with and without the pad soldered. Space between the leads and thermal pad should be as wide as possible to minimize the risk of contaminants affecting performance. A thorough washing of the board is recommended after the soldering process, especially if high accuracy performance is required at high temperatures. 06979-059 Figure 40. Functional Block Diagram CIRCUIT INFORMATION The AD8270 has two channels, each consisting of a high precision, low distortion op amp and seven trimmed resistors. These resistors can be connected to make a wide variety of amplifier configurations: difference, noninverting, inverting, and more. The resistors on the chip can be connected in parallel for a wider range of options. Using the on-chip resistors of the AD8270 provides the designer several advantages over a discrete design. DC Performance Much of the dc performance of op amp circuits depends on the accuracy of the surrounding resistors. The resistors on the AD8270 are laid out to be tightly matched. The resistors of each part are laser trimmed and tested for their matching accuracy. Because of this trimming and testing, the AD8270 can guarantee high accuracy for specifications such as gain drift, common-mode rejection, and gain error. AC Performance Because feature size is much smaller in an integrated circuit than on a PCB board, the corresponding parasitics are smaller, as well. The smaller feature size helps the ac performance of the AD8270. For example, the positive and negative input terminals of the AD8270 op amp are not pinned out intentionally. By not connecting these nodes to the traces on the PCB board, the capacitance remains low, resulting in both improved loop stability and common-mode rejection over frequency. REF1B 8 REF2B 7 REF1A 5 REF2A 6 POWER SUPPLIES A stable dc voltage should be used to power the AD8270. Noise on the supply pins can adversely affect performance. A bypass capacitor of 0.1 F should be placed between each supply pin and ground, as close as possible to each supply pin. A tantalum capacitor of 10 F should also be used 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. The AD8270 is specified at 15 V and 5 V, but it can be used with unbalanced supplies, as well. For example, -VS = 0 V, +VS = 20 V. The difference between the two supplies must be kept below 36 V. Production Costs Because one part, rather than several, is placed on the PCB board, the board can be built more quickly. Rev. 0 | Page 13 of 20 AD8270 INPUT VOLTAGE RANGE The AD8270 has a true rail-to-rail input range for the majority of applications. Because most AD8270 configurations divide down the voltage before they reach the internal op amp, the op amp sees only a fraction of the input voltage. Figure 41 shows an example of how the voltage division works in the difference amplifier configuration. R2 (V ) R1 + R2 +IN R4 R3 R1 R2 R2 (V ) R1 + R2 +IN 06979-061 The internal op amp voltage range may be relevant in the following applications, and calculating the voltage at the internal op amp is advised. * * * Difference amplifier configurations using supply voltages of less than 4.5 V Difference amplifier configurations with a reference voltage near the rail Single-ended amplifier configurations For correct operation, the input voltages at the internal op amp must stay within 1.5 V of either supply rail. Voltages beyond the supply rails should not be applied to the part. The part contains ESD diodes at the input pins, which conduct if voltages beyond the rails are applied. Currents greater than 5 mA can damage these diodes and the part. For a similar part that can operate with voltages beyond the rails, see the AD8273 data sheet. Figure 41. Voltage Division in the Difference Amplifier Configuration Rev. 0 | Page 14 of 20 AD8270 APPLICATIONS INFORMATION DIFFERENCE AMPLIFIER CONFIGURATIONS The AD8270 can be placed in difference amplifier configurations with gains of 0.5, 1, and 2. Figure 42 through Figure 44 show the difference amplifier configurations, referenced to ground. The AD8270 can also be referred to a combination of reference voltages. For example, the reference could be set at 2.5 V, using just 5 V and GND. Some of the possible configurations are shown in Figure 45 through Figure 47. The layout for Channel A is shown in Figure 42 through Figure 47. The layout for Channel B is symmetrical. Table 7 shows the pin connections for Channel A and Channel B. 16 1 10k 10k 10k 10k 20k 20k 5 6 15 SINGLE-ENDED CONFIGURATIONS The AD8270 can be configured for a wide variety of singleended configurations with gains ranging from -2 to +3. Table 8 shows a subset of the possible configurations. Many signal gains have more than one configuration choice, which allows freedom in choosing the op amp closed-loop gain. In general, for designs that need to be stable with a large capacitive load on the output, choose a configuration with high loop gain. Otherwise, choose a configuration with low loop gain, because these configurations typically have lower noise, lower offset, and higher bandwidth. 16 1 10k 10k 10k 10k 20k 20k 15 5k -IN = +IN 10k 5k -IN = +IN 10k 10k 5k 06979-056 10k 10k -IN +IN 2 3 4 -IN 10k 5k GND 06979-053 2 3 4 +IN 5 6 +VS + -VS 2 GND -VS +VS Figure 42. Gain = 0.5 Difference Amplifier, Referenced to Ground 16 15 Figure 45. Gain = 0.5 Difference Amplifier, Referenced to Midsupply 16 15 10k -IN = +IN 10k 10k 10k GND 06979-054 10k -IN = +IN 10k 10k 10k +VS + -VS 2 -IN NC NC +IN 1 2 3 4 10k 10k 10k 10k 10k -IN NC NC +IN 1 2 3 4 10k 10k 10k 10k 10k 20k 20k 5 6 20k 20k 5 6 GND NC = NO CONNECT -VS +VS NC = NO CONNECT Figure 43. Gain = 1 Difference Amplifier, Referenced to Ground 16 1 2 3 10k 10k 10k 10k 20k 20k 5 6 15 Figure 46. Gain = 1 Difference Amplifier, Referenced to Midsupply 16 1 2 3 10k 10k 10k 10k 20k 20k 15 10k -IN = +IN 5k 5k 10k -IN = +IN 5k 5k 10k +VS + -VS 06979-058 10k 10k -IN +IN -IN +IN 10k GND 06979-055 4 4 5 6 GND -VS +VS 2 Figure 44. Gain = 2 Difference Amplifier, Referenced to Ground Figure 47. Gain = 2 Difference Amplifier, Referenced to Midsupply Table 7. Pin Connections for Difference Amplifier Configurations Gain and Reference Gain of 0.5, Referenced to Ground Gain of 0.5, Referenced to Midsupply Gain of 1, Referenced to Ground Gain of 1, Referenced to Midsupply Gain of 2, Referenced to Ground Gain of 2, Referenced to Midsupply Pin 1 OUT OUT -IN -IN -IN -IN Pin 2 -IN -IN NC NC -IN -IN Channel A Pin 3 Pin 4 +IN GND +IN -VS NC +IN NC +IN +IN +IN +IN +IN Pin 5 GND +VS GND -VS GND -VS Pin 6 GND +VS GND +VS GND +VS Pin 12 OUT OUT -IN -IN -IN -IN Pin 11 -IN -IN NC NC -IN -IN Channel B Pin 10 Pin 9 +IN GND +IN -VS NC +IN NC +IN +IN +IN +IN +IN Pin 8 GND +VS GND -VS GND -VS Pin 7 GND +VS GND +VS GND +VS Rev. 0 | Page 15 of 20 06979-057 AD8270 Table 8. Selected Single-Ended Configurations Electrical Performance Signal Gain -2 -1.5 -1.4 -1.25 -1 -0.8 -0.667 -0.6 -0.5 -0.333 -0.25 -0.2 -0.125 +0.1 +0.2 +0.25 +0.3 +0.333 +0.375 +0.4 +0.5 +0.5 +0.6 +0.6 +0.625 +0.667 +0.7 +0.75 +0.75 +0.8 +0.9 +1 +1 +1 +1.125 +1.2 +1.2 +1.25 +1.333 +1.5 +1.5 +1.6 +1.667 +1.8 +2 +2.25 +2.4 +2.5 +3 Op Amp Closed-Loop Gain 3 3 3 3 3 3 2 2 2 2 1.5 1.5 1.5 1.5 2 1.5 1.5 2 1.5 2 3 1.5 3 1.5 1.5 2 1.5 3 1.5 2 1.5 1.5 1.5 3 1.5 3 1.5 1.5 2 3 1.5 2 2 3 2 3 3 3 3 Input Resistance 5 k 4.8 k 5 k 5.333 k 5 k 5.556 k 8 k 8.333 k 8.889 k 7.5 k 8 k 8.333 k 8.889 k 8.333 k 10 k 24 k 25 k 24 k 26.67 k 25 k 24 k 15 k 25 k 16.67 k 16 k 15 k 16.67 k 26.67 k 13.33 k 16.67 k 16.67 k 15 k >1 G >1 G 26.67 k 16.67 k 25 k 24 k 15 k 13.33 k >1 G 25 k 24 k 16.67 k >1 G 26.67 k 25 k 24 k >1 G 10 k - Pin 1 IN IN IN IN IN IN IN IN IN IN OUT OUT OUT OUT IN OUT OUT GND OUT GND GND OUT GND OUT OUT GND OUT GND OUT GND OUT OUT OUT IN OUT GND OUT OUT GND GND OUT GND GND GND GND GND GND GND GND Rev. 0 | Page 16 of 20 Pin Connections 10 k - Pin 2 IN IN IN IN IN IN NC NC NC NC IN IN IN IN NC GND GND NC GND NC GND GND GND GND IN NC IN GND GND NC GND GND IN IN GND GND GND GND NC GND GND NC NC GND NC GND GND GND GND 10 k + Pin 3 GND GND GND GND GND IN GND GND GND GND GND GND GND IN GND GND GND GND GND GND GND GND GND IN NC GND IN GND GND IN GND IN IN IN NC IN IN IN IN GND IN IN IN GND IN NC IN IN IN 10 k + Pin 4 GND GND GND NC GND GND GND GND NC GND GND GND NC GND IN GND GND GND NC GND GND GND GND GND IN GND IN NC IN GND IN IN IN IN IN GND IN IN IN IN IN IN IN IN IN IN IN IN IN 20 k + Pin 5 GND GND NC GND IN NC GND NC GND IN GND NC GND NC NC GND NC GND GND NC GND IN NC NC IN IN NC GND GND NC NC GND IN IN IN NC NC IN GND GND IN NC IN NC IN IN NC IN IN 20 k + Pin 6 GND IN IN IN IN GND IN IN IN IN IN IN IN GND IN IN IN IN IN IN IN IN IN GND GND IN GND IN IN GND IN GND IN IN GND GND GND GND GND IN IN GND GND IN IN GND GND GND IN AD8270 The AD8270 Specifications section and Typical Performance Characteristics section show the performance of the part primarily when it is in the difference amplifier configuration. To get a good estimate of the performance of the part in a single-ended configuration, refer to the difference amplifier configuration with the corresponding closed-loop gain (see Table 9). Table 9. Closed-Loop Gain of the Difference Amplifiers Difference Amplifier Gain 0.5 1 2 Closed-Loop Gain 1.5 2 3 +OUT 16 15 -OUT 14 13 V+IN - V-IN = V+OUT - V-OUT VOCM = V+OUT + V-OUT 10k 10k 10k 10k 12 11 10 9 1 10k 10k 10k 10k _ 10k 10k _ + -IN +IN 2 3 4 +IN -IN +IN +OUT VOCM -OUT + = -IN AD8270 20k 20k 20k 20k 5 6 7 8 OCM Figure 48. Differential Output, G = 1, Common-Mode Output Voltage Set with Reference Voltage +OUT 16 15 Gain of 1 Configuration The AD8270 is designed to be stable for loop gains of 1.5 and greater. Because a typical voltage follower configuration has a loop gain of 1, it may be unstable. Several stable G = 1 configurations are listed in Table 8. -OUT 14 13 1 10k 10k 10k 10k _ 10k 10k _ + 10k 10k 10k 10k 12 11 10 9 V+IN - V-IN = V+OUT - V-OUT V + VB V+OUT + V-OUT = A 2 +IN -IN A +IN +OUT VOCM -IN -OUT -IN +IN A 2 3 4 DIFFERENTIAL OUTPUT The AD8270 can easily be configured for differential output. Figure 48 shows the configuration for a G = 1 differential output amplifier. The OCM node in the figure sets the common-mode output voltage. Figure 49 shows the configuration for a G = 1 differential output amplifier, where the average of two voltages sets the common-mode output voltage. For example, this configuration can be used to set the common mode at 2.5 V, using just a 5 V reference and GND. + = AD8270 20k 20k 20k 20k 5 6 7 8 B Figure 49. Differential Output, G = 1, Common-Mode Output Voltage Set as the Average of Two Voltages Note that these two configurations are based on the G = 0.5 difference amplifier configurations shown in Figure 42 and Figure 45. A similar technique can be used to create differential output with a gain of 2 or 4, using the G = 1 and G = 2 difference amplifier configurations, respectively. Rev. 0 | Page 17 of 20 06979-063 VA + VB 2 06979-062 OCM AD8270 DRIVING AN ADC The AD270 high slew rate and drive capability, combined with its dc accuracy, make it a good ADC driver. The AD8270 can drive both single-ended and differential input ADCs. Many converters require the output to be buffered with a small value resistor combined with a high quality ceramic capacitor. See the converter data sheet for more details. Figure 51 shows the AD8270 in differential configuration, driving the AD7688 ADC. The AD8270 divides down the 5 V reference voltage from the ADR435, so that the common-mode output voltage is 2.5 V, which is precisely where the AD7688 needs it. To reduce the peaking, use a resistor between the AD8270 and the cable. Because cable capacitance and desired output response vary widely, this resistor is best determined empirically. A good starting point is 20 . AD8270 (DIFF OUT) DRIVING CABLING All cables have a certain capacitance per unit length, which varies widely with cable type. The capacitive load from the cable may cause peaking or instability in output response, especially when the AD8270 is operating in a gain of 0.5. (SINGLE OUT) AD8270 Figure 50. Driving Cabling +12V 16 -12V 13 10k 10k -IN +IN 2 3 4 5 6 1 NOTE: POWER SUPPLY DECOUPLING NOT SHOWN. 10k 10k 10k 20k 20k 20k 20k 10k 10k 10k 10k 10k 12 14 15 33 2.7nF COG 33 2.7nF COG 3 +IN AD7688 4 -IN REF 1 5V_REF 0.1F 7 8 9 AD8270 +12V 2 0.1F VIN VOUT 5 10F 5V_REF -IN +IN 10 11 ADR435 GND 4 Figure 51. Driving an ADC Rev. 0 | Page 18 of 20 06979-037 06979-060 AD8270 OUTLINE DIMENSIONS 4.00 BSC SQ 0.60 MAX 0.60 MAX 13 16 PIN 1 INDICATOR 1 PIN 1 INDICATOR TOP VIEW 0.65 BSC 3.75 BSC SQ 0.50 0.40 0.30 12 (BOTTOM VIEW) EXPOSED PAD 5 4 9 8 2.50 2.35 SQ 2.20 0.25 MIN 1.95 BSC 12 MAX 1.00 0.85 0.80 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM COMPLIANT TO JEDEC STANDARDS MO-220-VGGC Figure 52. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm x 4 mm Body, Very Thin Quad (CP-16-10) Dimensions are shown in millimeters ORDERING GUIDE Model AD8270ACPZ-R7 1 AD8270ACPZ-RL1 AD8270ACPZ-WP1 1 Temperature Range -40C to +85C -40C to +85C -40C to +85C Package Description 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ 010606-0 SEATING PLANE 0.35 0.30 0.25 0.20 REF COPLANARITY 0.08 Package Option CP-16-10 CP-16-10 CP-16-10 Z = RoHS Compliant Part. Rev. 0 | Page 19 of 20 AD8270 NOTES (c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06979-0-1/08(0) Rev. 0 | Page 20 of 20 |
Price & Availability of AD827008
 |
|
|
|
|
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] |