Low Noise, Precision CMOS Amplifier AD8655/AD8656 Data Sheet NC 1 -IN 2 AD8655 +IN 3 TOP VIEW (Not to Scale) V- 4 8 NC OUT A 1 7 V+ -IN A 2 6 OUT +IN A 3 5 NC NC = NO CONNECT Figure 1. AD8655 8-Lead MSOP (RM-8) 8-Lead SOIC (R-8) V- 4 AD8656 TOP VIEW (Not to Scale) 8 V+ 7 OUT B 6 -IN B 5 +IN B 05304-059 PIN CONFIGURATIONS Low noise: 2.7 nV/Hz at f = 10 kHz Low offset voltage: 250 V max over VCM Offset voltage drift: 0.4 V/C typ and 2.3 V/C max Bandwidth: 28 MHz Rail-to-rail input/output Unity gain stable 2.7 V to 5.5 V operation -40C to +125C operation Qualified for automotive applications 05304-048 FEATURES Figure 2. AD8656 8-Lead MSOP (RM-8) 8-Lead SOIC (R-8) APPLICATIONS ADC and DAC buffers Audio Industrial controls Precision filters Digital scales Automotive collision avoidance PLL filters GENERAL DESCRIPTION The AD8655/AD8656 are the industry's lowest noise, precision CMOS amplifiers. They leverage the Analog Devices DigiTrim(R) technology to achieve high dc accuracy. The AD8655/AD8656 provide low noise (2.7 nV/Hz at 10 kHz), low THD + N (0.0007%), and high precision performance (250 V max over VCM) to low voltage applications. The ability to swing rail-to-rail at the input and output enables designers to buffer analog-to-digital converters (ADCs) and other wide dynamic range devices in single-supply systems. The high precision performance of the AD8655/AD8656 improves the resolution and dynamic range in low voltage applications. Audio applications, such as microphone pre-amps and audio mixing consoles, benefit from the low noise, low distortion, and high output current capability of the AD8655/AD8656 to reduce system level noise performance and maintain audio fidelity. The high precision and rail-to-rail input and output of the AD8655/ AD8656 benefit data acquisition, process controls, and PLL filter applications. The AD8655/AD8656 are fully specified over the -40C to +125C temperature range. The AD8655/AD8656 are available in Pb-free, 8-lead MSOP and SOIC packages. The AD8655/ AD8656 are both available for automotive applications. Rev. E Document Feedback 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 (c)2005-2013 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com AD8655/AD8656 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Input Overvoltage Protection ................................................... 16 Applications ....................................................................................... 1 Input Capacitance ...................................................................... 16 Pin Configurations ........................................................................... 1 Driving Capacitive Loads .......................................................... 16 General Description ......................................................................... 1 Layout, Grounding, and Bypassing Considerations .................. 18 Revision History ............................................................................... 2 Power Supply Bypassing ............................................................ 18 Specifications..................................................................................... 3 Grounding ................................................................................... 18 Absolute Maximum Ratings............................................................ 5 Leakage Currents ........................................................................ 18 ESD Caution .................................................................................. 5 Outline Dimensions ....................................................................... 19 Typical Performance Characteristics ............................................. 6 Ordering Guide............................................................................... 19 Theory of Operation ...................................................................... 15 Automotive Products ................................................................. 19 Applications Information .............................................................. 16 REVISION HISTORY 10/13--Rev. D to Rev. E Changes to Figure 1 Caption and Figure 2 Caption .................... 1 Deleted Figure 3 and Figure 4; Renumbered Sequentially ......... 1 Change to General Description Section ........................................ 1 Change to Figure 4 ........................................................................... 6 Change to Figure 32 ....................................................................... 10 Changes to Ordering Guide .......................................................... 19 Changes to Automotive Products Section................................... 19 6/13--Rev. C to Rev. D Change to Figure 57 ....................................................................... 16 6/05--Rev. 0 to Rev. A Added AD8656 ................................................................... Universal Added Figure 2 and Figure 4 ...........................................................1 Changes to Specifications .................................................................3 Changed Caption of Figure 12 and Added Figure 13 ...................7 Replaced Figure 16 ............................................................................7 Changed Caption of Figure 37 and Added Figure 38 ................ 11 Replaced Figure 47 ......................................................................... 13 Added Figure 55 ............................................................................. 14 Changes to Ordering Guide .......................................................... 18 4/05--Revision 0: Initial Version 5/13--Rev. B to Rev. C Change to Figure 57 ....................................................................... 16 9/11--Rev. A to Rev. B Changes to Features Section............................................................ 1 Updated Outline Dimensions ....................................................... 19 Changes to Ordering Guide .......................................................... 19 Added Automotive Products Section .......................................... 19 Rev. E | Page 2 of 20 Data Sheet AD8655/AD8656 SPECIFICATIONS VS = 5.0 V, VCM = VS/2, TA = 25C, unless otherwise specified. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions VOS VCM = 0 V to 5 V -40C TA +125C -40C TA +125C Offset Voltage Drift Input Bias Current VOS/T IB Input Offset Current IOS Min Typ Max Unit 50 250 550 2.3 10 500 10 500 5 V V V/C pA pA pA pA V dB dB dB 0.4 1 -40C TA +125C -40C TA +125C Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier 0 85 100 95 CMRR AVO VCM = 0 V to 5 V VO = 0.2 V to 4.8 V, RL = 10 k, VCM = 0 V -40C TA +125C VOH VOL IOUT IL = 1 mA; -40C TA +125C IL = 1 mA; -40C TA +125C VOUT = 0.5 V 4.97 PSRR ISY VS = 2.7 V to 5.0 V VO = 0 V -40C TA +125C 88 INPUT CAPACITANCE Differential Common-Mode NOISE PERFORMANCE Input Voltage Noise Density CIN Total Harmonic Distortion + Noise FREQUENCY RESPONSE Gain Bandwidth Product Slew Rate Settling Time Phase Margin THD + N en GBP SR ts 100 110 4.991 8 220 105 3.7 30 4.5 5.3 V mV mA dB mA mA 9.3 16.7 pF pF f = 1 kHz f = 10 kHz G = 1, RL = 1 k, f = 1 kHz, VIN = 2 V p-p 4 2.7 0.0007 nV/Hz nV/Hz % RL = 10 k To 0.1%, VIN = 0 V to 2 V step, G = +1 CL = 0 pF 28 11 370 69 MHz V/s ns degrees Rev. E | Page 3 of 20 AD8655/AD8656 Data Sheet VS = 2.7 V, VCM = VS/2, TA = 25C, unless otherwise specified. Table 2. Parameter INPUT CHARACTERISTICS Offset Voltage Symbol Conditions VOS Offset Voltage Drift Input Bias Current VOS/T IB VCM = 0 V to 2.7 V -40C TA +125C -40C TA +125C Input Offset Current IOS Min Typ Max Unit 44 250 550 2.0 10 500 10 500 2.7 V V V/C pA pA pA pA V dB dB dB 0.4 1 -40C TA +125C -40C TA +125C Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Output Current POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier 0 80 98 90 CMRR AVO VCM = 0 V to 2.7 V VO = 0.2 V to 2.5 V, RL = 10 k, VCM = 0 V -40C TA +125C VOH VOL IOUT IL = 1 mA; -40C TA +125C IL = 1 mA; -40C TA +125C VOUT = 0.5 V 2.67 PSRR ISY VS = 2.7 V to 5.0 V VO = 0 V -40C TA +125C 88 INPUT CAPACITANCE Differential Common-Mode NOISE PERFORMANCE Input Voltage Noise Density CIN Total Harmonic Distortion + Noise FREQUENCY RESPONSE Gain Bandwidth Product Slew Rate Settling Time Phase Margin THD + N en GBP SR ts 98 2.688 10 75 105 3.7 30 4.5 5.3 V mV mA dB mA mA 9.3 16.7 pF pF f = 1 kHz f = 10 kHz G = 1, RL = 1k, f = 1 kHz, VIN = 2 V p-p 4.0 2.7 0.0007 nV/Hz nV/Hz % RL = 10 k To 0.1%, VIN = 0 to 1 V step, G = +1 CL = 0 pF 27 8.5 370 54 MHz V/s ns degrees Rev. E | Page 4 of 20 Data Sheet AD8655/AD8656 ABSOLUTE MAXIMUM RATINGS Table 4. Table 3. Parameter Supply Voltage Input Voltage Differential Input Voltage Output Short-Circuit Duration to GND Electrostatic Discharge (HBM) Storage Temperature Range R, RM Packages Junction Temperature Range R, RM Packages Lead Temperature (Soldering, 10 sec) Rating 6V VSS - 0.3 V to VDD + 0.3 V 6 V Indefinite Package Type 8-Lead MSOP (RM) 8-Lead SOIC (R) 3.0 kV -65C to +150C ESD CAUTION 1 JA1 210 158 JC 45 43 Unit C/W C/W JA is specified for worst-case conditions; that is, JA is specified for a device soldered in the circuit board for surface-mount packages. -65C to +150C 260C 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. Rev. E | Page 5 of 20 AD8655/AD8656 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 60 20 VS = 2.5V VS = 2.5V 10 40 VOS (V) 30 20 10 0 -10 05304-001 -20 0 -150 -100 -50 0 50 VOS (V) -30 150 100 05304-004 NUMBER OF AMPLIFIERS 50 0 Figure 3. Input Offset Voltage Distribution 1 2 3 4 COMMON-MODE VOLTAGE (V) 5 6 Figure 6. Input Offset Voltage vs. Common-Mode Voltage 250 250 VS = 2.5V VCM = 0V 200 VS = 2.5V 150 200 50 150 IB (pA) VOS (V) 100 0 -50 100 -100 +3 TYPICAL -3 -250 -50 25 0 -25 50 75 100 50 125 05304-005 -200 06304-004 -150 0 150 0 20 TEMPERATURE (C) 60 80 100 TEMPERATURE (C) 120 140 Figure 7. Input Bias Current vs. Temperature Figure 4. Input Offset Voltage vs. Temperature 60 4.0 VS = 2.5V VS = 2.5V 3.5 SUPPLY CURRENT (mA) 50 40 30 20 3.0 2.5 2.0 1.5 1.0 10 0 0 0.2 0.4 0.6 0.8 1.0 1.2 |TCVOS| (V/C) 1.4 05304-006 0.5 05304-003 NUMBER OF AMPLIFIERS 40 0 1.6 0 1 2 3 4 SUPPLY VOLTAGE (V) 5 Figure 8. Supply Current vs. Supply Voltage Figure 5. |TCVOS | Distribution Rev. E | Page 6 of 20 6 Data Sheet AD8655/AD8656 4.5 4.996 VS = 2.5V VS = 2.5V LOAD CURRENT = 1mA 4.994 4.992 3.5 VOH (V) SUPPLY CURRENT (mA) 4.0 3.0 4.990 4.988 4.986 2.5 2.0 -50 0 50 TEMPERATURE (C) 100 4.982 -50 150 0 50 TEMPERATURE (C) 100 12 2500 LOAD CURRENT = 1mA VS = 2.5V VS = 2.5V 10 1500 8 VOL (mV) 2000 VOH 1000 6 VOL 05304-008 0 50 100 150 CURRENT LOAD (mA) 200 05304-010 4 500 0 2 -50 250 0 50 TEMPERATURE (C) 100 150 Figure 13. Output Voltage Swing Low vs. Temperature Figure 10. AD8655 Output Voltage to Supply Rail vs. Current Load 120 10000 VS = 2.5V VIN = 28mV RL = 1M CL = 47pF VS = 2.5V 100 1000 CMRR (dB) 80 100 60 40 10 VOL VOH 1 0.1 1 10 CURRENT LOAD (mA) 100 0 100 1000 05304-011 20 05304-056 DELTA SWING FROM SUPPLY (mV) 150 Figure 12. Output Voltage Swing High vs. Temperature Figure 9. Supply Current vs. Temperature DELTA SWING FROM SUPPLY (mV) 05304-009 05304-007 4.984 1k 10k 100k FREQUENCY (Hz) Figure 14. CMRR vs. Frequency Figure 11. AD8656 Output Swing vs. Current Load Rev. E | Page 7 of 20 1M 10M AD8655/AD8656 Data Sheet 100 110.00 VS = 2.5V VCM = 0V CMRR (dB) 104.00 101.00 98.00 05304-012 95.00 92.00 -50 0 50 TEMPERATURE (C) 100 10 05304-019 VOLTAGE NOISE DENSITY (nV/Hz 1/2) VS = 2.5V 107.00 1 1 150 Figure 15. Large Signal CMRR vs. Temperature 10 100 1k FREQUENCY (Hz) 10k 100k Figure 18. Voltage Noise Density vs. Frequency 100 +PSRR -PSRR 500nV/DIV PSRR (dB) 80 VS = 2.5V Vn (p-p) = 1.23V VS = 2.5V VIN = 50mV RL = 1M CL = 47pF 60 40 1 05304-013 0 100 05304-020 20 1k 10k 100k 1M FREQUENCY (Hz) 10M 1s/DIV 100M Figure 16. Small Signal PSSR vs. Frequency Figure 19. Low Frequency Noise (0.1 Hz to 10 Hz). 110.00 VIN VS = 2.5V VOUT 1V/DIV 106.00 VS = 2.5V CL = 50pF GAIN = +1 2 104.00 100.00 -50 05304-021 102.00 05304-014 PSRR (dB) 108.00 T 0 50 TEMPERATURE (C) 100 20s/DIV 150 Figure 17. Large Signal PSSR vs. Temperature Figure 20. No Phase Reversal Rev. E | Page 8 of 20 Data Sheet AD8655/AD8656 -45 120 6 100 5 PHASE MARGIN = 69 PHASE SHIFT (Degrees) -90 60 40 -135 20 -180 0 4 OUTPUT (V) 80 GAIN (dB) VS = 2.5V VIN = 5V G = +1 VS = 2.5V CLOAD = 11.5pF 3 2 1 100k 1M FREQUENCY (Hz) -225 100M 10M 05304-018 -40 10k 05304-015 -20 0 10k Figure 21. Open-Loop Gain and Phase vs. Frequency 100k 1M FREQUENCY (Hz) Figure 24. Maximum Output Swing vs. Frequency 140.00 T VS = 2.5V CL = 100pF GAIN = +1 VIN = 4V VS = 2.5V RL = 10k VOUT (1V/DIV) 130.00 AVO (dB) 10M 120.00 110.00 2 05304-016 05304-022 100.00 90.00 -50 0 50 TEMPERATURE (C) 100 TIME (10s/DIV) 150 Figure 22. Large Signal Open-Loop Gain vs. Temperature Figure 25. Large Signal Response 50 T VS = 2.5V RL = 1M CL = 47pF VS = 2.5V CL = 100pF G = +1 VOUT (100mV/DIV) 30 20 10 2 -10 -20 1k 05304-023 0 05304-017 CLOSED-LOOP GAIN (dB) 40 10k 100k 1M FREQUENCY (Hz) 10M 100M TIME (1s/DIV) Figure 23. Closed-Loop Gain vs. Frequency Figure 26. Small Signal Response Rev. E | Page 9 of 20 AD8655/AD8656 Data Sheet 100 30 OUTPUT IMPEDANCE () 25 OVERSHOOT % VS = 2.5V VS = 2.5V VIN = 200mV 20 -OS 15 10 +OS G = +100 G = +1 G = +10 10 1 0 0 50 100 150 200 250 CAPACITANCE (pF) 300 0.1 100 350 Figure 27. Small Signal Overshoot vs. Load Capacitance 05304-027 05304-024 5 1k 10k 100k FREQUENCY (Hz) 1M 10M 100M Figure 30. Output Impedance vs. Frequency 80 T VS = 1.35V 300mV VIN 70 NUMBER OF AMPLIFIERS 0V 1 0V 2 VS = 2.5V VIN = 300mV GAIN = -10 RECOVERY TIME = 240ns 05304-025 -2.5V 50 40 30 20 10 05304-028 VOUT 60 0 400ns/DIV -150 -125 -100 -75 -50 -25 0 25 VOS (V) Figure 28. Negative Overload Recovery Time 50 75 100 125 150 Figure 31. Input Offset Voltage Distribution 250 T VS = 1.35V VCM = 0V 200 0V 1 VIN 150 VS = 2.5V VIN = 300mV GAIN = -10 RECOVERY TIME = 240ns 100 VOS (V) -300mV 2.5V VOUT 50 0 -50 -100 +3 TYPICAL -3 05304-026 -150 -200 -250 -50 400ns/DIV -25 0 25 50 75 100 06304-032 0V 2 125 TEMPERATURE (C) Figure 29. Positive Overload Recovery Time Figure 32. Input Offset Voltage vs. Temperature Rev. E | Page 10 of 20 150 Data Sheet AD8655/AD8656 10000 80 VS = 1.35V VS = 1.35V 60 50 40 30 20 100 0 0 0.2 0.4 0.6 0.8 1.0 1.2 |TCVOS| (V/C) 1.4 VOL 10 05304-030 10 1000 05304-057 DELTA OUTPUT FROM SUPPLY (mV) NUMBER OF AMPLIFIERS 70 VOH 1 0.1 1.6 Figure 33. |TCVOS| Distribution 1 10 CURRENT LOAD (mA) 100 Figure 36. AD8656 Output Swing vs. Current Load 4.5 2.698 VS = 1.35V 2.694 2.690 3.5 VOH (V) 2.686 3.0 2.682 2.5 2.0 -50 0 50 TEMPERATURE (C) 100 2.674 -50 150 05304-032 05304-031 2.678 0 50 TEMPERATURE (C) 100 150 Figure 37. Output Voltage Swing High vs. Temperature Figure 34. Supply Current vs. Temperature 14 1400 VS = 1.35V LOAD CURRENT = 1mA VS = 1.35V 1200 12 1000 10 VOL (mV) VOH 800 600 6 VOL 400 8 4 05304-050 200 0 0 20 40 60 80 LOAD CURRENT (mA) 100 2 -50 120 05304-033 SUPPLY CURRENT (mA) 4.0 (VSY-VOUT) (mV) VS = 1.35V LOAD CURRENT = 1mA 0 50 TEMPERATURE (C) 100 Figure 38. Output Voltage Swing Low vs. Temperature Figure 35. AD8655 Output Voltage to Supply Rail vs. Load Current Rev. E | Page 11 of 20 150 AD8655/AD8656 Data Sheet 35 T VS = 1.35V G = +1 CL = 50pF VIN VS = 1.35V VIN = 200mV 30 -OS 25 OVERSHOOT % 1V/DIV VOUT 2 20 15 +OS 10 05304-044 05304-047 5 0 20s/DIV 0 200 250 150 CAPACITANCE (pF) 300 350 Figure 42. Small Signal Overshoot vs. Load Capacitance Figure 39. No Phase Reversal T VS = 1.35V CL = 50pF GAIN = +1 100 50 T 200mV VIN 2 0V 2 VOUT -1.35V 05304-042 VS = 1.35V VIN = 200mV GAIN = -10 RECOVERY TIME = 180ns 400ns/DIV TIME (10s/DIV) Figure 43. Negative Overload Recovery Time Figure 40. Large Signal Response T T VS = 1.35V CL = 100pF GAIN = +1 0V 1 VIN VS = 1.35V VIN = 200mV GAIN = -10 RECOVERY TIME = 200ns -200mV 2 1.35V VOUT 0V 2 05304-046 05304-043 VOUT (100mV/DIV) 05304-045 VOUT (500mV/DIV) 0V 1 TIME (1s/DIV) 400ns/DIV Figure 44. Positive Overload Recovery Time Figure 41. Small Signal Response Rev. E | Page 12 of 20 Data Sheet AD8655/AD8656 120 120 VS = 1.35V VIN = 28mV RL = 1M CL = 47pF 100 PHASE MARGIN = 54 80 60 GAIN (dB) CMRR (dB) -90 80 PHASE SHIFT (Degrees) 100 -45 VS = 1.35V CLOAD = 11.5pF 60 40 -135 20 40 -180 0 20 0 100 1k 10k FREQUENCY (Hz) 100k -40 10k 1M 100k 1M FREQUENCY (Hz) 05304-036 05304-034 -20 -225 100M 10M Figure 48. Open-Loop Gain and Phase vs. Frequency Figure 45. CMRR vs. Frequency 102.00 130.00 VS = 1.35V VS = 1.35V RL = 10k 120.00 AVO (dB) CMRR (dB) 98.00 94.00 110.00 100.00 90.00 86.00 -50 0 50 TEMPERATURE (C) 100 80.00 -50 150 0 50 TEMPERATURE (C) 100 150 Figure 49. Large Signal Open-Loop Gain vs. Temperature Figure 46. Large Signal CMRR vs. Temperature 50 100 80 VS = 1.35V VIN = 50mV RL = 1M CL = 47pF VS = 1.35V RL = 1M CL = 47pF 40 CLOSED-LOOP GAIN (dB) +PSRR -PSRR 60 40 30 20 10 0 20 1k 10k 100k 1M FREQUENCY (Hz) 10M -20 1k 100M 05304-038 0 100 -10 05304-040 PSRR (dB) 05304-037 05304-035 90.00 10k 100k 1M FREQUENCY (Hz) 10M Figure 50. Closed-Loop Gain vs. Frequency Figure 47. Small Signal PSSR vs. Frequency Rev. E | Page 13 of 20 100M AD8655/AD8656 Data Sheet 0 3.0 2.5 CHANNEL SEPERATION (dB) 1.5 1.0 0.5 100k 1M FREQUENCY (Hz) G = +100 G = +10 G = +1 1 05304-041 OUTPUT IMPEDANCE () 100 10k 100k 1M FREQUENCY (Hz) 10M B V+ -60 -80 -100 100 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 53. Channel Separation vs. Frequency VS = 1.35V 1k V- VOUT -2.5V 10 1000 0.1 100 - A -140 10M Figure 51. Maximum Output Swing vs. Frequency 10 -40 + -120 05304-039 0 10k V- V+ VIN 50mV p-p VS = 2.5V VIN = 50mV R2 100 05304-058 OUTPUT (V) 2.0 VS = 1.35V VIN = 2.7V G = +1 NO LOAD R1 10k +2.5V -20 100M Figure 52. Output Impedance vs. Frequency Rev. E | Page 14 of 20 100M Data Sheet AD8655/AD8656 THEORY OF OPERATION The AD8655/AD8656 amplifiers are voltage feedback, rail-to-rail input and output precision CMOS amplifiers, which operate from 2.7 V to 5.0 V of power supply voltage. These amplifiers use the Analog Devices DigiTrim technology to achieve a higher degree of precision than is available from most CMOS amplifiers. DigiTrim technology, used in a number of Analog Devices amplifiers, is a method of trimming the offset voltage of the amplifier after it is packaged. The advantage of post-package trimming is that it corrects any offset voltages caused by the mechanical stresses of assembly. The AD8655/AD8656 can be used in any precision op amp application. The amplifier does not exhibit phase reversal for common-mode voltages within the power supply. The AD8655/ AD8656 are great choices for high resolution data acquisition systems with voltage noise of 2.7 nV/Hz and THD + Noise of -103 dB for a 2 V p-p signal at 10 kHz. Their low noise, sub-pA input bias current, precision offset, and high speed make them superb preamps for fast filter applications. The speed and output drive capability of the AD8655/AD8656 also make them useful in video applications. The AD8655/AD8656 are available in standard op amp pinouts, making DigiTrim completely transparent to the user. The input stage of the amplifiers is a true rail-to-rail architecture, allowing the input common-mode voltage range of the amplifiers to extend to both positive and negative supply rails. The openloop gain of the AD8655/AD8656 with a load of 10 k is typically 110 dB. Rev. E | Page 15 of 20 AD8655/AD8656 Data Sheet APPLICATIONS INFORMATION INPUT OVERVOLTAGE PROTECTION The internal protective circuitry of the AD8655/AD8656 allows voltages exceeding the supply to be applied at the input. It is recommended, however, not to apply voltages that exceed the supplies by more than 0.3 V at either input of the amplifier. If a higher input voltage is applied, series resistors should be used to limit the current flowing into the inputs. The input current should be limited to less than 5 mA. One simple technique for compensation is a snubber that consists of a simple RC network. With this circuit in place, output swing is maintained, and the amplifier is stable at all gains. Figure 55 shows the implementation of a snubber, which reduces overshoot by more than 30% and eliminates ringing. Using a snubber does not recover the loss of bandwidth incurred from a heavy capacitive load. VS = 2.5V AV = 1 CL = 500pF VOLTAGE (100mV/DIV) The extremely low input bias current allows the use of larger resistors, which allows the user to apply higher voltages at the inputs. The use of these resistors adds thermal noise, which contributes to the overall output voltage noise of the amplifier. For example, a 10 k resistor has less than 12.6 nV/Hz of thermal noise and less than 10 nV of error voltage at room temperature. Along with bypassing and ground, high speed amplifiers can be sensitive to parasitic capacitance between the inputs and ground. For circuits with resistive feedback network, the total capacitance, whether it is the source capacitance, stray capacitance on the input pin, or the input capacitance of the amplifier, causes a breakpoint in the noise gain of the circuit. As a result, a capacitor must be added in parallel with the gain resistor to obtain stability. The noise gain is a function of frequency and peaks at the higher frequencies, assuming the feedback capacitor is selected to make the second-order system critically damped. A few picofarads of capacitance at the input reduce the input impedance at high frequencies, which increases the amplifier's gain, causing peaking in the frequency response or oscillations. With the AD8655/AD8656, additional input damping is required for stability with capacitive loads greater than 200 pF with direct input to output feedback. See the Driving Capacitive Loads section. TIME (2s/DIV) Figure 54. Driving Heavy Capacitive Loads Without Compensation VCC +IN - + 200 + - 200mV VEE 500pF 500pF 05304-052 -IN VS = 2.5V AV = 1 RS = 200 CS = 500pF CL = 500pF TIME (10s/DIV) 05304-053 VOLTAGE (100mV/DIV) Figure 55. Snubber Network DRIVING CAPACITIVE LOADS Although the AD8655/AD8656 can drive capacitive loads up to 500 pF without oscillating, a large amount of ringing is present when operating the part with input frequencies above 100 kHz. This is especially true when the amplifiers are configured in positive unity gain (worst case). When such large capacitive loads are required, the use of external compensation is highly recommended. This reduces the overshoot and minimizes ringing, which, in turn, improves the stability of the AD8655/ AD8656 when driving large capacitive loads. 05304-051 INPUT CAPACITANCE Figure 56. Driving Heavy Capacitive Loads Using a Snubber Network Rev. E | Page 16 of 20 Data Sheet AD8655/AD8656 THD Readings vs. Common-Mode Voltage 1.0 Total harmonic distortion of the AD8655/AD8656 is well below 0.0007% with a load of 1 k. This distortion is a function of the circuit configuration, the voltage applied, and the layout, in addition to other factors. 0.5 SWEEP 2: VIN = 2V p-p RL = 1k 0.1 0.05 0.02 % +2.5V SWEEP 1: VIN = 2V p-p RL = 10k 0.2 0.01 0.005 - VOUT 0.002 AD8655 0.001 RL + SWEEP 2 SWEEP 1 0.0002 0.0001 Figure 57. THD + N Test Circuit 05304-055 VIN 05304-054 0.0005 -2.5V 20 50 100 200 500 1k Hz 2k 5k 10k 20k 50k 80k Figure 58. THD + Noise vs. Frequency Rev. E | Page 17 of 20 AD8655/AD8656 Data Sheet LAYOUT, GROUNDING, AND BYPASSING CONSIDERATIONS POWER SUPPLY BYPASSING LEAKAGE CURRENTS Power supply pins can act as inputs for noise, so care must be taken to apply a noise-free, stable dc voltage. The purpose of bypass capacitors is to create low impedances from the supply to ground at all frequencies, thereby shunting or filtering most of the noise. Bypassing schemes are designed to minimize the supply impedance at all frequencies with a parallel combination of capacitors with values of 0.1 F and 4.7 F. Chip capacitors of 0.1 F (X7R or NPO) are critical and should be as close as possible to the amplifier package. The 4.7 F tantalum capacitor is less critical for high frequency bypassing, and, in most cases, only one is needed per board at the supply inputs. Poor PC board layout, contaminants, and the board insulator material can create leakage currents that are much larger than the input bias current of the AD8655/AD8656. Any voltage differential between the inputs and nearby traces creates leakage currents through the PC board insulator, for example, 1 V/100 G = 10 pA. Similarly, any contaminants on the board can create significant leakage (skin oils are a common problem). GROUNDING A ground plane layer is important for densely packed PC boards to minimize parasitic inductances. This minimizes voltage drops with changes in current. However, an understanding of where the current flows in a circuit is critical to implementing effective high speed circuit design. The length of the current path is directly proportional to the magnitude of parasitic inductances, and, therefore, the high frequency impedance of the path. Large changes in currents in an inductive ground return create unwanted voltage noise. To significantly reduce leakage, put a guard ring (shield) around the inputs and input leads that are driven to the same voltage potential as the inputs. This ensures there is no voltage potential between the inputs and the surrounding area to create any leakage currents. To be effective, the guard ring must be driven by a relatively low impedance source and should completely surround the input leads on all sides, above and below, by using a multilayer board. The charge absorption of the insulator material itself can also cause leakage currents. Minimizing the amount of material between the input leads and the guard ring helps to reduce the absorption. Also, using low absorption materials, such as Teflon(R) or ceramic, may be necessary in some instances. The length of the high frequency bypass capacitor leads is critical, and, therefore, surface-mount capacitors are recommended. A parasitic inductance in the bypass ground trace works against the low impedance created by the bypass capacitor. Because load currents flow from the supplies, the ground for the load impedance should be at the same physical location as the bypass capacitor grounds. For larger value capacitors intended to be effective at lower frequencies, the current return path distance is less critical. Rev. E | Page 18 of 20 Data Sheet AD8655/AD8656 OUTLINE DIMENSIONS 3.20 3.00 2.80 5.00 (0.1968) 4.80 (0.1890) 5 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) 8 3.20 3.00 2.80 0.50 (0.0196) 0.25 (0.0099) 45 5.15 4.90 4.65 4 PIN 1 IDENTIFIER 8 0 0.25 (0.0098) 0.17 (0.0067) 1 5 0.65 BSC 0.95 0.85 0.75 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-012-AA 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. 15 MAX 1.10 MAX 0.15 0.05 COPLANARITY 0.10 0.40 0.25 6 0 0.80 0.55 0.40 0.23 0.09 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 60. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Figure 59. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) ORDERING GUIDE Model1, 2 AD8655ARZ AD8655ARZ-REEL AD8655ARZ-REEL7 AD8655ARMZ-REEL AD8655ARMZ AD8655WARMZ-RL AD8656ARZ AD8656ARZ-REEL AD8656ARZ-REEL7 AD8656ARMZ AD8656ARMZ-REEL AD8656WARMZ-REEL 1 2 Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP Package Option R-8 R-8 R-8 RM-8 RM-8 RM-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 Branding A0D A0D A0D A0S A0S A0S Z = RoHS Compliant Part. W = Qualified for Automotive Applications. AUTOMOTIVE PRODUCTS The AD8655W model and the AD8656W model are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for this model. Rev. E | Page 19 of 20 10-07-2009-B 1 012407-A 8 4.00 (0.1574) 3.80 (0.1497) AD8655/AD8656 Data Sheet NOTES (c)2005-2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05304-0-10/13(E) Rev. E | Page 20 of 20