ANALOG DEVICES ADA4891-2

Low Cost CMOS, High Speed, Rail-to-Rail Amplifiers Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 FEATURES CONNECTION DIAGRAMS Qualified for automotive applications (ADA4891-1W, ADA4891-1 ADA4891-2W only) NC 1 8 NC High speed and fast settling –IN 2 7 +V S +IN 3 6 OUT −3 dB bandwidth: 220 MHz (G = +1) –V 4 5 NC S Slew rate: 170 V/µs Settling time to 0.1%: 28 ns NC = NO CONNECT Video specifications (G = +2, RL = 150 Ω) Figure 1. 8-Lead SOIC_N (R-8) 0.1 dB gain flatness: 25 MHz ADA4891-1 Differential gain error: 0.05% 1 +V OUT 5 S Differential phase error: 0.25° Single-supply operation –V 2 S Wide supply range: 2.7 V to 5.5 V +IN 3 4 –IN Output swings to within 50 mV of supply rails Low distortion: 79 dBc SFDR at 1 MHz Figure 2. 5-Lead SOT-23 (RJ-5) Linear output current: 125 mA at −40 dBc ADA4891-2 Low power: 4.4 mA per amplifier OUT1 1 8 +V S APPLICATIONS –IN1 2 7 OUT2 Automotive infotainment systems +IN1 3 6 –IN2 Automotive driver assistance systems –V 4 5 +IN2 S Imaging NC = NO CONNECT Consumer video Figure 3. 8-Lead SOIC_N (R-8) and 8-Lead MSOP (RM-8) Active filters ADA4891-3 Coaxial cable drivers PD1 1 14 OUT2 Clock buffers PD2 2 13 –IN2 Photodiode preamp Contact image sensor and buffers PD3 3 12 +IN2 +V 4 11 –V S S GENERAL DESCRIPTION +IN1 5 10 +IN3 The ADA4891-1 (single), ADA4891-2 (dual), ADA4891-3 (triple), –IN1 6 9 –IN3 and ADA4891-4 (quad) are CMOS, high speed amplifiers that OUT1 7 8 OUT3 offer high performance at a low cost. The amplifiers feature true single-supply capability, with an input voltage range that extends Figure 4. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14) 300 mV below the negative rail. ADA4891-4 In spite of their low cost, the ADA4891 family provides high 1 14 OUT4 OUT1 performance and versatility. The rail-to-rail output stage enables –IN1 2 13 –IN4 the output to swing to within 50 mV of each rail, enabling maxi- 3 12 +IN4 +IN1 mum dynamic range. 4 11 +V –V S S The ADA4891 family of amplifiers is ideal for imaging applica- 5 10 +IN3 +IN2 tions, such as consumer video, CCD buffers, and contact image 6 –IN3 –IN2 9 sensor and buffers. Low distortion and fast settling time also 7 8 OUT3 OUT2 make them ideal for active filter applications. Figure 5. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14) The ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 are avail- able in a wide variety of packages. The ADA4891-1 is available 14-lead TSSOP packages. The amplifiers are specified to operate in 8-lead SOIC and 5-lead SOT-23 packages. The ADA4891-2 over the extended temperature range of −40°C to +125°C. is available in 8-lead SOIC and 8-lead MSOP packages. The ADA4891-3 and ADA4891-4 are available in 14-lead SOIC and Rev. D 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 ©2010–2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 08054-001 08054-026 08054-027 08054-074 08054-073 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Effect of R on 0.1 dB Gain Flatness ........................................ 16 F Applications ....................................................................................... 1 Driving Capacitive Loads .......................................................... 17 General Description ......................................................................... 1 Terminating Unused Amplifiers .............................................. 18 Connection Diagrams ...................................................................... 1 Disable Feature (ADA4891-3 Only) ........................................ 18 Revision History ............................................................................... 2 Single-Supply Operation ........................................................... 18 Specifications ..................................................................................... 3 Video Reconstruction Filter ...................................................... 19 5 V Operation ............................................................................... 3 Multiplexer .................................................................................. 19 3 V Operation ............................................................................... 4 Layout, Grounding, and Bypassing .............................................. 20 Absolute Maximum Ratings ............................................................ 6 Power Supply Bypassing ............................................................ 20 Maximum Power Dissipation ..................................................... 6 Grounding ................................................................................... 20 ESD Caution .................................................................................. 6 Input and Output Capacitance ................................................. 20 Typical Performance Characteristics ............................................. 7 Input-to-Output Coupling ........................................................ 20 Applications Information .............................................................. 15 Leakage Currents ........................................................................ 20 Using the ADA4891 ................................................................... 15 Outline Dimensions ....................................................................... 21 Wideband, Noninverting Gain Operation .............................. 15 Ordering Guide .......................................................................... 23 Wideband, Inverting Gain Operation ..................................... 15 Automotive Products ................................................................. 23 Recommended Values ................................................................ 15 REVISION HISTORY 3/12—Rev. C to Rev. D Added Table 4; Renumbered Tables Sequentially ......................... 6 Added ADA4891-1W and ADA4891-2W ...................... Universal Deleted Figure 11 ............................................................................... 6 Changes to Features Section and Applications Section ............... 1 Changes to Typical Performance Characteristics Section ........... 7 Changes to Input Offset Voltage, Input Bias Current, and Open- Deleted Figure 12 ............................................................................... 7 Loop Gain Parameters, Table 1 ....................................................... 4 Changes to Wideband, Noninverting Gain Operation Section, Changes to Input Offset Voltage, Input Bias Current, and Open- Wideband, Inverting Gain Operation Section, and Table 5 ..... 15 Loop Gain Parameters, Table 2 ....................................................... 5 Added Table 6 ................................................................................. 16 Changes to Ordering Guide .......................................................... 23 Changes to Figure 52 ...................................................................... 16 Added Figure 53 ............................................................................. 16 Added Automotive Products Section .......................................... 23 Changed Layout of Driving Capacitive Loads Section .............. 17 9/10—Rev. B to Rev. C Added Disable Feature (ADA4891-3 Only) Section Changes to Figure 23 and Figure 24 ............................................... 9 and Single-Supply Operation Section .......................................... 18 Added Multiplexer Section ........................................................... 19 7/10—Rev. A to Rev. B Updated Outline Dimensions ....................................................... 21 Added ADA4891-3 and ADA4891-4 ............................... Universal Changes to Ordering Guide .......................................................... 23 Added 14-Lead SOIC and 14-Lead TSSOP Packages .... Universal Deleted Figure 4; Renumbered Figures Sequentially ................... 1 6/10—Rev. 0 to Rev. A Changes to Features Section and General Description Section . 1 Changes to Figure 26 ......................................................................... 9 Added Figure 4 and Figure 5 ........................................................... 1 Changes to Figure 33 and Figure 34............................................. 10 Changes to Table 1 ............................................................................ 3 Updated Outline Dimensions ....................................................... 18 Changes to Table 2 ............................................................................ 4 Changes to Ordering Guide .......................................................... 18 Changes to Maximum Power Dissipation Section and Figure 6 ....................................................................................... 6 2/10—Revision 0: Initial Version Rev. D | Page 2 of 24 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 SPECIFICATIONS 5 V OPERATION T = 25°C, V = 5 V, R = 1 kΩ to 2.5 V, unless otherwise noted. All specifications are for the ADA4891-1, ADA4891-2, ADA4891-3, and A S L ADA4891-4, unless otherwise noted. For the ADA4891-1 and ADA4891-2, R = 604 Ω; for the ADA4891-3 and ADA4891-4, R = 453 Ω, F F unless otherwise noted. Table 1. Parameter Test Conditions/Comments Min Typ Max Unit DYNAMIC PERFORMANCE −3 dB Small-Signal Bandwidth ADA4891-1/ADA4891-2, G = +1, V = 0.2 V p-p 240 MHz O ADA4891-3/ADA4891-4, G = +1, V = 0.2 V p-p 220 MHz O ADA4891-1/ADA4891-2, G = +2, VO = 0.2 V p-p, 90 MHz RL = 150 Ω to 2.5 V ADA4891-3/ADA4891-4, G = +2, V = 0.2 V p-p, 96 MHz O R = 150 Ω to 2.5 V L Bandwidth for 0.1 dB Gain Flatness ADA4891-1/ADA4891-2, G = +2, V = 2 V p-p, 25 MHz O RL = 150 Ω to 2.5 V, RF = 604 Ω ADA4891-3/ADA4891-4, G = +2, VO = 2 V p-p, 25 MHz RL = 150 Ω to 2.5 V, RF = 374 Ω Slew Rate, t /t G = +2, V = 2 V step, 10% to 90% 170/210 V/µs R F O −3 dB Large-Signal Frequency Response G = +2, V = 2 V p-p, R = 150 Ω 40 MHz O L Settling Time to 0.1% G = +2, V = 2 V step 28 ns O NOISE/DISTORTION PERFORMANCE Harmonic Distortion, HD2/HD3 f = 1 MHz, V = 2 V p-p, G = +1 −79/−93 dBc C O fC = 1 MHz, VO = 2 V p-p, G = −1 −75/−91 dBc Input Voltage Noise f = 1 MHz 9 nV/√Hz Differential Gain Error (NTSC) G = +2, RL = 150 Ω to 2.5 V 0.05 % Differential Phase Error (NTSC) G = +2, R = 150 Ω to 2.5 V 0.25 Degrees L All-Hostile Crosstalk f = 5 MHz, G = +2, V = 2 V p-p −80 dB O DC PERFORMANCE Input Offset Voltage ±2.5 ±10 mV ADA4891-1W/ADA4891-2W only, T to T ±3.1 ±16 mV MIN MAX T to T ±3.1 mV MIN MAX Offset Drift 6 µV/°C Input Bias Current −50 +2 +50 pA ADA4891-1W/ADA4891-2W only, TMIN to TMAX −50 +50 nA Open-Loop Gain R = 1 kΩ to 2.5 V 77 83 dB L ADA4891-1W/ADA4891-2W only, T to T , 66 dB MIN MAX RL = 1 kΩ to 2.5 V RL = 150 Ω to 2.5 V 71 dB INPUT CHARACTERISTICS Input Resistance 5 GΩ Input Capacitance 3.2 pF Input Common-Mode Voltage Range −VS − 0.3 to V +V − 0.8 S Common-Mode Rejection Ratio (CMRR) V = 0 V to 3.0 V 88 dB CM OUTPUT CHARACTERISTICS Output Voltage Swing R = 1 kΩ to 2.5 V 0.01 to 4.98 V L R = 150 Ω to 2.5 V 0.08 to 4.90 V L Output Current 1% THD with 1 MHz, V = 2 V p-p 125 mA O Short-Circuit Current Sourcing 205 mA Sinking 307 mA Rev. D | Page 3 of 24 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet Parameter Test Conditions/Comments Min Typ Max Unit POWER-DOWN PINS (PD1, PD2, PD3) ADA4891-3 only Threshold Voltage, VTH 2.4 V Bias Current Part enabled 65 nA Part powered down −22 µA Turn-On Time Part enabled, output rises to 90% of final value 166 ns Turn-Off Time 49 ns Part powered down, output falls to 10% of final value POWER SUPPLY Operating Range 2.7 5.5 V Quiescent Current per Amplifier 4.4 mA Supply Current When Powered Down ADA4891-3 only 0.8 mA Power Supply Rejection Ratio (PSRR) Positive PSRR +V = 5 V to 5.25 V, −V = 0 V 65 dB S S Negative PSRR +V = 5 V, −V = −0.25 V to 0 V 63 dB S S OPERATING TEMPERATURE RANGE −40 +125 °C 3 V OPERATION T = 25°C, V = 3 V, R = 1 kΩ to 1.5 V, unless otherwise noted. All specifications are for the ADA4891-1, ADA4891-2, ADA4891-3, and A S L ADA4891-4, unless otherwise noted. For the ADA4891-1 and ADA4891-2, RF = 604 Ω; for the ADA4891-3 and ADA4891-4, RF = 453 Ω, unless otherwise noted. Table 2. Parameter Test Conditions/Comments Min Typ Max Unit DYNAMIC PERFORMANCE −3 dB Small-Signal Bandwidth ADA4891-1/ADA4891-2, G = +1, VO = 0.2 V p-p 190 MHz ADA4891-3/ADA4891-4, G = +1, VO = 0.2 V p-p 175 MHz ADA4891-1/ADA4891-2, G = +2, VO = 0.2 V p-p, 75 MHz R = 150 Ω to 1.5 V L ADA4891-3/ADA4891-4, G = +2, V = 0.2 V p-p, 80 MHz O R = 150 Ω to 1.5 V L Bandwidth for 0.1 dB Gain Flatness ADA4891-1/ADA4891-2, G = +2, VO = 2 V p-p, 18 MHz RL = 150 Ω to 1.5 V, RF = 604 Ω ADA4891-3/ADA4891-4, G = +2, VO = 2 V p-p, 18 MHz R = 150 Ω to 1.5 V, R = 374 Ω L F Slew Rate, t /t G = +2, V = 2 V step, 10% to 90% 140/230 V/µs R F O −3 dB Large-Signal Frequency Response G = +2, VO = 2 V p-p, RL = 150 Ω 40 MHz Settling Time to 0.1% G = +2, VO = 2 V step 30 ns NOISE/DISTORTION PERFORMANCE Harmonic Distortion, HD2/HD3 fC = 1 MHz, VO = 2 V p-p, G = −1 −70/−89 dBc Input Voltage Noise f = 1 MHz 9 nV/√Hz Differential Gain Error (NTSC) G = +2, RL = 150 Ω to 0.5 V, +VS = 2 V, −VS = −1 V 0.23 % Differential Phase Error (NTSC) G = +2, R = 150 Ω to 0.5 V, +V = 2 V, −V = −1 V 0.77 Degrees L S S All-Hostile Crosstalk f = 5 MHz, G = +2 −80 dB DC PERFORMANCE Input Offset Voltage ±2.5 ±10 mV ADA4891-1W/ADA4891-2W only, T to T ±3.1 ±16 mV MIN MAX T to T ±3.1 mV MIN MAX Offset Drift 6 µV/°C Input Bias Current −50 +2 +50 pA ADA4891-1W/ADA4891-2W only, TMIN to TMAX −50 +50 nA Rev. D | Page 4 of 24 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Parameter Test Conditions/Comments Min Typ Max Unit Open-Loop Gain RL = 1 kΩ to 1.5 V 72 76 dB ADA4891-1W/ADA4891-2W only, TMIN to TMAX, 60 dB RL = 1 kΩ to 1.5 V R = 150 Ω to 1.5 V 65 dB L INPUT CHARACTERISTICS Input Resistance 5 GΩ Input Capacitance 3.2 pF Input Common-Mode Voltage Range −V − 0.3 to V S +VS − 0.8 Common-Mode Rejection Ratio (CMRR) VCM = 0 V to 1.5 V 87 dB OUTPUT CHARACTERISTICS Output Voltage Swing RL = 1 kΩ to 1.5 V 0.01 to 2.98 V RL = 150 Ω to 1.5 V 0.07 to 2.87 V Output Current 1% THD with 1 MHz, VO = 2 V p-p 37 mA Short-Circuit Current Sourcing 80 mA Sinking 163 mA POWER-DOWN PINS (PD1, PD2, PD3) ADA4891-3 only Threshold Voltage, V 1.3 V TH Bias Current Part enabled 48 nA Part powered down −13 µA Turn-On Time Part enabled, output rises to 90% of final value 185 ns Turn-Off Time Part powered down, output falls to 10% of final 58 ns value POWER SUPPLY Operating Range 2.7 5.5 V Quiescent Current per Amplifier 3.5 mA Supply Current When Powered Down ADA4891-3 only 0.73 mA Power Supply Rejection Ratio (PSRR) Positive PSRR +VS = 3 V to 3.15 V, −VS = 0 V 76 dB Negative PSRR +VS = 3 V, −VS = −0.15 V to 0 V 72 dB OPERATING TEMPERATURE RANGE −40 +125 °C Rev. D | Page 5 of 24 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet ABSOLUTE MAXIMUM RATINGS To ensure proper operation, it is necessary to observe the maxi- Table 3. mum power derating curves shown in Figure 6. These curves Parameter Rating are derived by setting TJ = 150°C in Equation 1. Figure 6 shows Supply Voltage 6 V the maximum safe power dissipation in the package vs. the Input Voltage (Common Mode) −V − 0.5 V to +V S S ambient temperature on a JEDEC standard 4-layer board. Differential Input Voltage ±V S 2.0 Storage Temperature Range −65°C to +125°C T = 150°C J 14-LEAD TSSOP Operating Temperature Range −40°C to +125°C Lead Temperature (Soldering, 10 sec) 300°C 1.5 8-LEAD SOIC_N Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress 1.0 rating only; functional operation of the device at these or any 8-LEAD MSOP other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute 5-LEAD SOT-23 0.5 maximum rating conditions for extended periods may affect 14-LEAD SOIC_N device reliability. MAXIMUM POWER DISSIPATION 0 –55 –35 –15 5 25 45 65 85 105 125 The maximum power that can be safely dissipated by the AMBIENT TEMPERATURE (°C) ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 is limited Figure 6. Maximum Power Dissipation vs. Ambient Temperature by the associated rise in junction temperature. The maximum Table 4 lists the thermal resistance (θ ) for each ADA4891-1/ safe junction temperature for plastic encapsulated devices is JA ADA4891-2/ADA4891-3/ADA4891-4 package. determined by the glass transition temperature of the plastic, approximately 150°C. Temporarily exceeding this limit can Table 4. cause a shift in parametric performance due to a change in the Package Type θ Unit JA stresses exerted on the die by the package. Exceeding a junction 5-Lead SOT-23 146 °C/W temperature of 175°C for an extended period can result in 8-Lead SOIC_N 115 °C/W device failure. 8-Lead MSOP 133 °C/W The still-air thermal properties of the package (θ ), the ambient JA 14-Lead SOIC_N 162 °C/W temperature (TA), and the total power dissipated in the package 14-Lead TSSOP 108 °C/W (PD) can be used to determine the junction temperature of the die. The junction temperature can be calculated as ESD CAUTION TJ = TA + (PD × θJA) (1) The power dissipated in the package (P ) is the sum of the D quiescent power dissipation and the power dissipated in the package due to the load drive for all outputs. It can be calculated by P = (V × I ) + (V − V ) × (V /R ) (2) D T S S OUT OUT L where: VT is the total supply rail. IS is the quiescent current. V is the positive supply rail. S V is the output of the amplifier. OUT R is the output load of the amplifier. L Rev. D | Page 6 of 24 MAXIMUM POWER DISSIPATION (W) 08054-002 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 TYPICAL PERFORMANCE CHARACTERISTICS Unless otherwise noted, all plots are characterized for the ADA4891-1, ADA4891-2, ADA4891-3, and ADA4891-4. For the ADA4891-1 and ADA4891-2, the typical RF value is 604 Ω. For the ADA4891-3 and ADA4891-4, the typical RF value is 453 Ω. 4 5 4 3 3 G = –1 OR +2 2 2 G = +1 1 1 0 0 –1 G = +1 G = –1 –1 OR +2 –2 –2 –3 –3 –4 G = +10 –4 G = +5 G = +5 –5 –5 –6 –6 –7 G = +10 –7 V = 5V S V = 5V S V = 200mV p-p OUT –8 V = 200mV p-p OUT –8 R = 453Ω F R = 604Ω F –9 –9 R = 1kΩ L R = 1kΩ L –10 –10 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 7. Small-Signal Frequency Response vs. Gain, VS = 5 V, Figure 10. Small-Signal Frequency Response vs. Gain, VS = 5 V, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 6 6 V = 2.7V S V = 3V S V = 2.7V S 3 V = 3V S 3 0 0 V = 5V S V = 5V S –3 –3 –6 –6 –9 –9 G = +1 –12 –12 G = +1 V = 200mV p-p OUT V = 200mV p-p R = 1kΩ OUT L R = 1kΩ L –15 –15 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 8. Small-Signal Frequency Response vs. Supply Voltage, Figure 11. Small-Signal Frequency Response vs. Supply Voltage, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 5 5 +125°C +85°C 4 4 +25°C 0°C +25°C 3 3 –40°C +85°C 0°C 2 +125°C 2 1 1 –40°C 0 0 –1 –1 –2 –2 V = 5V S V = 5V S G = +1 G = +1 –3 –3 V = 200mV p-p OUT V = 200mV p-p OUT R = 1kΩ R = 1kΩ L L –4 –4 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 9. Small-Signal Frequency Response vs. Temperature, VS = 5 V, Figure 12. Small-Signal Frequency Response vs. Temperature, VS = 5 V, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 Rev. D | Page 7 of 24 CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) CLOSED-LOOP GAIN (dB) 08054-030 08054-028 08054-029 CLOSED-LOOP GAIN (dB) CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-078 08054-077 08054-076 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet 7 7 +25°C +85°C 6 6 +85°C –40°C +125°C 5 0°C 5 +25°C +125°C 0°C 4 4 3 3 2 2 1 1 0 0 –40°C –1 –1 –2 –2 –3 –3 V = 3V V = 3V –4 S –4 S G = +1 G = +1 V = 200mV p-p V = 200mV p-p –5 –5 OUT OUT R = 1kΩ R = 1kΩ L L –6 –6 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 13. Small-Signal Frequency Response vs. Temperature, VS = 3 V, Figure 16. Small-Signal Frequency Response vs. Temperature, VS = 3 V, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 0.1 0.1 0 0 V = 3V S V = 5V S V = 2V p-p OUT V = 1.4V p-p OUT –0.1 –0.1 V = 5V S V = 1.4V p-p OUT –0.2 –0.2 V = 3V S V = 2V p-p OUT –0.3 V = 5V –0.3 S V = 5V V = 2V p-p S OUT V = 2V p-p OUT –0.4 –0.4 G = +2 G = +2 V = 3V S R = 374Ω R = 604Ω F V = 3V F V = 1.4V p-p S OUT R = 150Ω R = 150Ω L L V = 1.4V p-p OUT –0.5 –0.5 0.1 1 10 100 0.1 1 10 100 FREQUENCY (MHz) FREQUENCY (MHz) Figure 14. 0.1 dB Gain Flatness vs. Supply Voltage, G = +2, Figure 17. 0.1 dB Gain Flatness vs. Supply Voltage, G = +2, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 1 1 0 0 G = –1 R = 453Ω F –1 G = +1 –1 R = 0Ω G = +2 F –2 R = 604Ω –2 F G = +5 G = +1 –3 –3 R = 453Ω F R = 0Ω F –4 –4 G = +5 R = 604Ω F G = –1 –5 –5 R = 604Ω F –6 –6 –7 –7 V = 5V –8 –8 S R = 150Ω V = 5V S L G = +2 –9 R = 150Ω –9 V = 2V p-p L OUT R = 453Ω V = 2V p-p OUT F –10 –10 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 15. Large-Signal Frequency Response vs. Gain, V = 5 V, S Figure 18. Large-Signal Frequency Response vs. Gain, VS = 5 V, ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 Rev. D | Page 8 of 24 CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-019 08054-036 08054-031 CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-081 08054-080 08054-079 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 1 1 0 0 G = –1 G = –1 –1 V = 2V p-p –1 OUT V = 2V p-p OUT G = +2 V = 2V p-p –2 –2 OUT G = +2 G = +1 –3 –3 G = +1 V = 2V p-p OUT V = 1V p-p OUT V = 1V p-p OUT –4 –4 G = +5 –5 –5 V = 2V p-p OUT G = +5 –6 –6 V = 2V p-p OUT –7 –7 V = 3V V = 3V –8 –8 S S R = 604Ω R = 453Ω F F –9 R = 150Ω –9 R = 150Ω L L –10 –10 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 19. Large-Signal Frequency Response vs. Gain, V = 3 V, Figure 22. Large-Signal Frequency Response vs. Gain, V = 3 V, S S ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 –40 –30 V = 5V V = 3V S S R = 1kΩ L R = 1kΩ L G = +2 –50 V = 2V p-p OUT V = 2V p-p OUT SECOND HARMONIC –40 G = +1 THIRD HARMONIC –60 G = +2 –50 SECOND HARMONIC –70 G = +1 G = +1 SECOND HARMONIC SECOND HARMONIC –80 –60 +V = +1.9V S –90 –70 –100 OUT G = +2 THIRD HARMONIC IN 1kΩ –80 50Ω –110 G = +2 = –1.1V –V S G = +1 THIRD HARMONIC THIRD HARMONIC G = +1 CONFIGURATION –120 –90 0.1 1 10 0.1 1 10 FREQUENCY (MHz) FREQUENCY (MHz) Figure 20. Harmonic Distortion (HD2, HD3) vs. Frequency, VS = 5 V Figure 23. Harmonic Distortion (HD2, HD3) vs. Frequency, VS = 3 V –40 –40 V = 5V G = +1 S +V = +1.9V G = +1 S SECOND HARMONIC R = 604Ω F CONFIGURATION –50 G = +1 R = 1kΩ –50 L SECOND HARMONIC f = 1MHz C OUT –60 IN 1kΩ –60 50Ω G = –1 SECOND HARMONIC –70 –70 –V = –1.1V S –80 –80 –90 –90 G = –1 SECOND HARMONIC G = –1 –100 –100 G = –1 G = +1 THIRD HARMONIC THIRD HARMONIC THIRD HARMONIC –110 –110 G = +1 V = 3V S THIRD HARMONIC f = 1MHz C –120 –120 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.51.01.52.02.53.0 OUTPUT VOLTAGE (V p-p) OUTPUT VOLTAGE (V p-p) Figure 21. Harmonic Distortion (HD2, HD3) vs. Output Voltage, VS = 5 V Figure 24. Harmonic Distortion (HD2, HD3) vs. Output Voltage, VS = 3 V Rev. D | Page 9 of 24 0 DISTORTION (dBc) DISTORTION (dBc) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-037 08054-040 08054-038 DISTORTION (dBc) DISTORTION (dBc) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-082 08054-039 08054-041 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet –40 1k G = +2 V = 3V S R = 604Ω F SECOND HARMONIC R = 150Ω L V = 3V S –50 f = 1MHz C THIRD HARMONIC –60 100 –70 V = 5V S V = 5V S THIRD HARMONIC SECOND HARMONIC –80 10 –90 V = 5V S G = +1 –100 1 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 00.5 1.0 10 100 1k 10k 100k 1M 10M OUTPUT VOLTAGE (V p-p) FREQUENCY (Hz) Figure 25. Harmonic Distortion (HD2, HD3) vs. Output Voltage, G = +2 Figure 28. Input Voltage Noise vs. Frequency 90 0 0.06 V = 5V S 0.04 R = 1kΩ L 80 –18 0.02 70 –36 0 GAIN –0.02 60 –54 V = 5V, G = +2 S –0.04 R = 604Ω, R = 150Ω F L 50 –72 –0.06 PHASE ST ND RD TH TH TH TH TH TH TH 1 2 3 4 5 6 7 8 9 10 40 –90 0.3 30 –108 0.2 0.1 20 –126 0 10 –144 –0.1 V = 5V, G = +2 S –0.2 0 –162 R = 604Ω, R = 150Ω F L –0.3 –10 –180 ST ND RD TH TH TH TH TH TH TH 1 2 3 4 5 6 7 8 9 10 0.001 0.01 0.1 1 10 100 1k MODULATING RAMP LEVEL (IRE) FREQUENCY (MHz) Figure 29. Differential Gain and Phase Errors Figure 26. Open-Loop Gain and Phase vs. Frequency 7 7 6 6 5 5 C = 47pF C = 47pF L L 4 4 C = 22pF L C = 22pF 3 L 3 C = 10pF L 2 2 C = 10pF L 1 1 0 0 C = 0pF L –1 C = 0pF –1 L V = 5V V = 5V S –2 –2 S G = +2 G = +2 R = 150Ω R = 150Ω –3 L –3 L V = 200mV p-p V = 200mV p-p OUT OUT –4 –4 0.1 1 10 100 1k 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 27. Small-Signal Frequency Response vs. C , Figure 30. Small-Signal Frequency Response vs. C , L L ADA4891-1/ADA4891-2 ADA4891-3/ADA4891-4 Rev. D | Page 10 of 24 OPEN-LOOP GAIN (dB) DISTORTION (dBc) NORMALIZED CLOSED-LOOP GAIN (dB) 08054-044 08054-042 PHASE (Degrees) 08054-043 VOLTAGE NOISE (nV/ Hz) DIFFERENTIAL DIFFERENTIAL NORMALIZED CLOSED-LOOP GAIN (dB) PHASE ERROR (Degrees) GAIN ERROR (%) 08054-083 08054-060 08054-045 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 100 100k V = 5V S G = +1 10k 10 1k 1 100 0.1 10 V = 5V S G = +1 0.01 1 0.01 0.1 1 10 100 0.01 0.1 1 10 100 FREQUENCY (MHz) FREQUENCY (MHz) Figure 31. Closed-Loop Output Impedance vs. Frequency, Part Enabled Figure 34. Closed-Loop Output Impedance vs. Frequency, Part Disabled (ADA4891-3 Only) 1.5 G = +1 G = +2 V = 5V S V = 200mV p-p OUT V = 2V p-p R = 1kΩ OUT L V = 3V R = 1kΩ S L 1.0 100 V = 5V S V = 3V S R = 150Ω L R = 150Ω L 0.5 V = 5V S V = 3V S R = 1kΩ L 0 0 –0.5 –100 –1.0 50mV/DIV 5ns/DIV –1.5 10 20 30 40 50 60 70 80 90 TIME (ns) Figure 32. Small-Signal Step Response, G = +1 Figure 35. Large-Signal Step Response, G = +2 V = 5V V = 3V S S R = 1kΩ R = 1kΩ G = +1 L G = +1 L V = 1V p-p OUT V = 2V p-p OUT 1 0.5 R = 150Ω L R = 150Ω L 0 0 –1 –0.5 5ns/DIV 0.5V/DIV 5ns/DIV 0.5V/DIV Figure 33. Large-Signal Step Response, V = 5 V, G = +1 Figure 36. Large-Signal Step Response, VS = 3 V, G = +1 S Rev. D | Page 11 of 24 OUTPUT IMPEDANCE (Ω) OUTPUT VOLTAGE (mV) OUTPUT VOLTAGE (V) 08054-049 08054-048 08054-046 OUTPUT IMPEDANCE (Ω) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 08054-050 08054-047 08054-089 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet 0.30 200 V = 5V S V =5V G = +2 S G=+2 R = 150Ω L 0.20 190 R = 150Ω L V =2Vp-p OUT FALLING EDGE 0.10 180 0 170 –0.10 160 RISING EDGE –0.20 150 –0.30 140 025 30 35 40 45 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 TIME (ns) OUTPUT STEP (V) Figure 37. Short-Term Settling Time to 0.1% Figure 40. Slew Rate vs. Output Step 3 1 V = ±2.5V V = ±2.5V S S G = +1 G = +1 INPUT R = 1kΩ R = 1kΩ L L INPUT 2 OUTPUT 0 1 –1 OUTPUT 0 –2 1V/DIV 5ns/DIV 1V/DIV 5ns/DIV –1 –3 Figure 38. Input Overdrive Recovery from Positive Rail Figure 41. Input Overdrive Recovery from Negative Rail 3 3 V = ±2.5V S V = ±2.5V S OUTPUT INPUT G = –2 G = –2 R = 1kΩ L R = 1kΩ L 2 2 1 1 INPUT 0 0 –1 –1 –2 –2 OUTPUT 1V/DIV 5ns/DIV 1V/DIV 5ns/DIV –3 –3 Figure 39. Output Overdrive Recovery from Positive Rail Figure 42. Output Overdrive Recovery from Negative Rail Rev. D | Page 12 of 24 SETTLING (%) AMPLITUDE (V) AMPLITUDE (V) 08054-070 08054-071 08054-061 SLEW RATE (V/µs) AMPLITUDE (V) AMPLITUDE (V) 08054-052 08054-063 08054-051 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 –10 0 V = 5V V = 5V S S –10 G = +2 –20 R = 150Ω L –20 –30 –30 –40 TSSOP –40 –50 –50 –60 –60 SOIC –70 –70 –80 –80 –90 –100 –90 0.01 0.1 1 10 100 0.1 1 10 100 1k FREQUENCY (MHz) FREQUENCY (MHz) Figure 43. CMRR vs. Frequency Figure 46. Forward Isolation vs. Frequency (ADA4891-3 Only) –10 1.0 Vs = 5V V = 5V S G = +1 G = –2 0.9 R = 604Ω F –20 0.8 –30 0.7 V , +125°C OH V , +25°C OH V , –40°C 0.6 OH –40 V , +125°C OL V , +25°C +PSRR OL 0.5 V , –40°C OL –50 0.4 0.3 –60 –PSRR 0.2 –70 0.1 0 –80 0.01 0.1 1 10 100 0 10 20 30 40 50 60 70 80 90 100 FREQUENCY (MHz) I (mA) LOAD Figure 44. PSRR vs. Frequency Figure 47. Output Saturation Voltage vs. Load Current and Temperature 0 6.0 Vs = 5V V = 5V S G = +2 –10 R = 1 kΩ L V = 2V p-p 5.5 OUT –20 –30 5.0 –40 –50 4.5 –60 4.0 –70 –80 3.5 –90 –100 3.0 0.1 1 10 100 1k –40 –20 0 20 40 60 80 100 120 FREQUENCY (MHz) TEMPERATURE (ºC) Figure 45. All-Hostile Crosstalk (Output-to-Output) vs. Frequency Figure 48. Supply Current per Amplifier vs. Temperature Rev. D | Page 13 of 24 CMRR (dB) CROSSTALK (dB) PSRR (dB) 08054-072 08054-054 08054-090 OUTPUT SATURATION VOLTAGE (V) QUIESCENT SUPPLY CURRENT (mA) ISOLATION (dB) 08054-084 08054-057 08054-056 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 SUPPLY VOLTAGE (V) Figure 49. Supply Current per Amplifier vs. Supply Voltage Rev. D | Page 14 of 24 QUIESCENT SUPPLY CURRENT (mA) 08054-058 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 APPLICATIONS INFORMATION WIDEBAND, INVERTING GAIN OPERATION USING THE ADA4891 +V S Understanding the subtleties of the ADA4891 family of amplifiers provides insight into how to extract the peak performance from 0.1µF 10µF the device. The following sections describe the effect of gain, component values, and parasitics on the performance of the V O ADA4891. The wideband, noninverting gain configuration of ADA4891 the ADA4891 is shown in Figure 50; the wideband, inverting R L 50Ω gain configuration of the ADA4891 is shown in Figure 51. SOURCE R R G F V I WIDEBAND, NONINVERTING GAIN OPERATION R T +V S 0.1µF 10µF 0.1µF 10µF 50Ω –V S SOURCE Figure 51. Inverting Gain Configuration V I V O R ADA4891 T Figure 51 shows the inverting gain configuration. For the R L inverting gain configuration, set the parallel combination of R F RT and RG to match the input source impedance. R G Note that a bias current cancellation resistor is not required in 0.1µF 10µF the noninverting input of the amplifier because the input bias current of the ADA4891 is very low (less than 2 pA). Therefore, –V the dc errors caused by the bias current are negligible. S Figure 50. Noninverting Gain Configuration For both noninverting and inverting gain configurations, it is often useful to increase the RF value to decrease the load on the In Figure 50, R and R denote the feedback and gain resistors, F G output. Increasing the RF value improves harmonic distortion at respectively. Together, RF and RG determine the noise gain of the the expense of reducing the 0.1 dB bandwidth of the amplifier. amplifier. The value of RF defines the 0.1 dB bandwidth (for This effect is discussed further in the Effect of R on 0.1 dB Gain F more information, see the Effect of RF on 0.1 dB Gain Flatness Flatness section. section). Typical RF values range from 549 Ω to 698 Ω for the ADA4891-1/ADA4891-2. Typical R values range from 301 Ω F RECOMMENDED VALUES to 453 Ω for the ADA4891-3/ADA4891-4. Table 5 and Table 6 provide a quick reference for various configu- In a controlled impedance signal path, R is used as the input T rations and show the effect of gain on the −3 dB small-signal termination resistor designed to match the input source imped- bandwidth, slew rate, and peaking of the ADA4891-1/ADA4891-2/ ance. Note that RT is not required for normal operation. RT is ADA4891-3/ADA4891-4. Note that as the gain increases, the generally set to match the input source impedance. small-signal bandwidth decreases, as is expected from the gain bandwidth product relationship. In addition, the phase margin improves with higher gains, and the amplifier becomes more stable. As a result, the peaking in the frequency response is reduced (see Figure 7 and Figure 10). Table 5. Recommended Component Values and Effect of Gain on ADA4891-1/ADA4891-2 Performance (R = 1 kΩ) L Feedback Network Values −3 dB Small-Signal Bandwidth (MHz) Slew Rate (V/µs) Gain RF (Ω) RG (Ω) VOUT = 200 mV p-p tR tF Peaking (dB) −1 604 604 118 188 192 1.3 +1 0 Open 240 154 263 2.6 +2 604 604 120 170 210 1.4 +5 604 151 32.5 149 154 0 +10 604 67.1 12.7 71 72 0 Rev. D | Page 15 of 24 08054-023 08054-024 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet Table 6. Recommended Component Values and Effect of Gain on ADA4891-3/ADA4891-4 Performance (R = 1 kΩ) L Feedback Network Values −3 dB Small-Signal Bandwidth (MHz) Slew Rate (V/µs) Gain RF (Ω) RG (Ω) VOUT = 200 mV p-p tR tF Peaking (dB) −1 453 453 97 186 194 0.9 +1 0 Open 220 151 262 4.1 +2 453 453 97 181 223 0.9 +5 453 90.6 31 112 120 0 +10 453 45.3 13 68 67 0 0.3 EFFECT OF R ON 0.1 dB GAIN FLATNESS F R = R = 453Ω G F 0.2 R = R = 402Ω G F Gain flatness is an important specification in video applications. R = R = 357Ω G F It represents the maximum allowable deviation in the signal 0.1 amplitude within the pass band. Tests have revealed that the 0 human eye is unable to distinguish brightness variations of less than 1%, which translates into a 0.1 dB signal drop within R = R = 301Ω –0.1 G F the pass band or, put simply, 0.1 dB gain flatness. –0.2 The PCB layout configuration and bond pads of the chip often contribute to stray capacitance. The stray capacitance at the –0.3 V = 5V S inverting input forms a pole with the feedback and gain resistors. G = +2 –0.4 V = 2V p-p OUT This additional pole adds phase shift and reduces phase margin R = 150Ω L –0.5 in the closed-loop phase response, causing instability in the 0.1 1 10 100 amplifier and peaking in the frequency response. FREQUENCY (MHz) Figure 52 and Figure 53 show the effect of using various values Figure 53. 0.1 dB Gain Flatness, Noninverting Gain Configuration, ADA4891-3/ADA4891-4 for Feedback Resistor R on the 0.1 dB gain flatness of the parts. F Figure 52 shows the effect for the ADA4891-1/ADA4891-2. To obtain the desired 0.1 dB bandwidth, adjust the feedback Figure 53 show the effect for the ADA4891-3/ADA4891-4. resistor, RF, as shown in Figure 52 and Figure 53. If RF cannot Note that a larger RF value causes more peaking because the be adjusted, a small capacitor can be placed in parallel with RF additional pole formed by RF and the input stray capacitance to reduce peaking. shifts down in frequency and interacts significantly with the The feedback capacitor, C , forms a zero with the feedback F internal poles of the amplifier. resistor, which cancels out the pole formed by the input stray 0.2 capacitance and the gain and feedback resistors. For a first pass R = R = 698Ω G F R = R = 649Ω G F in determining the C value, use the following equation: F R = R = 604Ω G F 0.1 RG × CS = RF × CF 0 where: R = R = 549Ω G F RG is the gain resistor. –0.1 C is the input stray capacitance. S R is the feedback resistor. F –0.2 C is the feedback capacitor. F Using this equation, the original closed-loop frequency response of V = 5V S –0.3 G = +2 the amplifier is restored, as if there is no stray input capacitance. V = 2V p-p OUT R = 150Ω Most often, however, the value of CF is determined empirically. L –0.4 0.1 1 10 100 Figure 54 shows the effect of using various values for the FREQUENCY (MHz) feedback capacitor to reduce peaking. In this case, the Figure 52. 0.1 dB Gain Flatness, Noninverting Gain Configuration, ADA4891-1/ ADA4891-2 are used for demonstration purposes ADA4891-1/ADA4891-2 and R = R = 604 Ω. The input stray capacitance, together with F G the board parasitics, is approximately 2 pF. Rev. D | Page 16 of 24 NORMALIZED CLOSED-LOOP GAIN (dB) 08054-022 NORMALIZED CLOSED-LOOP GAIN (dB) 08054-085 Data Sheet ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 0.2 These four methods minimize the output capacitive loading effect. C = 0pF • Reducing the output resistive load. This pushes the pole F 0.1 further away and, therefore, improves the phase margin. C = 1pF F • Increasing the phase margin with higher noise gains. As 0 the closed-loop gain is increased, the larger phase margin allows for large capacitive loads with less peaking. C = 3.3pF F • Adding a parallel capacitor (C ) with R , from −IN to the F F –0.1 output. This adds a zero in the closed-loop frequency response, which tends to cancel out the pole formed by the V = 5V –0.2 S G = +2 capacitive load and the output impedance of the amplifier. R = 604Ω F R = 150Ω See the Effect of RF on 0.1 dB Gain Flatness section for L V = 2V p-p OUT –0.3 more information. 0.1 1 10 100 • Placing a small value resistor (R ) in series with the output S FREQUENCY (MHz) to isolate the load capacitor from the output stage of the Figure 54. 0.1 dB Gain Flatness vs. C , V = 5 V, F S amplifier. ADA4891-1/ADA4891-2 Figure 57 shows the effect of using a snub resistor (R ) on reducing DRIVING CAPACITIVE LOADS S the peaking in the worst-case frequency response (gain of +1). A highly capacitive load reacts with the output impedance of Using RS = 100 Ω reduces the peaking by 3 dB, with the trade-off the amplifiers, causing a loss of phase margin and subsequent that the closed-loop gain is reduced by 0.9 dB due to attenuation peaking or even oscillation. The ADA4891-1/ADA4891-2 are at the output. RS can be adjusted from 0 Ω to 100 Ω to maintain used to demonstrate this effect (see Figure 55 and Figure 56). an acceptable level of peaking and closed-loop gain, as shown in 8 Figure 57. 6 8 V = 5V S V = 200mV p-p 4 OUT 6 G = +1 R = 1kΩ L 2 C = 6.8pF 4 L 0 2 R = 0Ω –2 S 0 –4 R = 100Ω S –2 –6 V = 5V S –4 V = 200mV p-p OUT R S G = +1 –8 V OUT IN –6 R = 1kΩ L 200mV C = 6.8pF R L C L L STEP –10 –8 50Ω 0.1 1 10 100 FREQUENCY (MHz) –10 0.1 1 10 100 Figure 55. Closed-Loop Frequency Response, CL = 6.8 pF, FREQUENCY (MHz) ADA4891-1/ADA4891-2 Figure 57. Closed-Loop Frequency Response with Snub Resistor, CL = 6.8 pF Figure 58 shows that the transient response is also much improved V = 5V S G = +1 by the snub resistor (RS = 100 Ω) compared to that of Figure 56. R = 1kΩ L C = 6.8pF L V = 5V S G = +1 100 R = 1kΩ L C = 6.8pF L R = 100Ω S 100 0 0 –100 –100 50mV/DIV 50ns/DIV Figure 56. 200 mV Step Response, CL = 6.8 pF, ADA4891-1/ADA4891-2 50mV/DIV 50ns/DIV Figure 58. 200 mV Step Response, CL = 6.8 pF, RS = 100 Ω Rev. D | Page 17 of 24 NORMALIZED CLOSED-LOOP GAIN (dB) OUTPUT VOLTAGE (mV) MAGNITUDE (dB) 08054-034 08054-032 08054-025 MAGNITUDE (dB) OUTPUT VOLTAGE (mV) 08054-035 08054-033 ADA4891-1/ADA4891-2/ADA4891-3/ADA4891-4 Data Sheet TERMINATING UNUSED AMPLIFIERS SINGLE-SUPPLY OPERATION Terminating unused amplifiers in a multiamplifier package is The ADA4891 can also be operated from a single power supply. an important step in ensuring proper operation of the functional Figure 61 shows the ADA4891-3 configured as a single 5 V amplifier. Unterminated amplifiers can oscillate and draw supply video driver. excessive power. The recommended procedure for terminating • The input signal is ac-coupled into the amplifier via unused amplifiers is to connect any unused amplifiers in a Capacitor C1. unity-gain configuration and to connect the noninverting input • Resistor R2 and Resistor R4 establish the input midsupply to midsupply voltage. With symmetrical bipolar power supplies, reference for the amplifier. this means connecting the noninverting input to ground, as • Capacitor C5 prevents constant current from being drawn shown in Figure 59. through the gain set resistor (R ) and enables the ADA4891-3 G +V S at dc to provide unity gain to the input midsupply voltage, thereby establishing the output voltage at midsupply. • Capacitor C6 is the output coupling capacitor. ADA4891 The large-signal frequency response obtained with single- supply operation is identical to the bipolar supply operation –V S (Figure 18 shows the large-signal frequency response). Figure 59. Terminating Unused Amplifier with Four pairs of low frequency poles are formed by R2/2 and C2, Symmetrical Bipolar Power Supplies R3 and C1, R and C5, and R and C6. With this configuration, G L In single power supply applications, a synthetic midsupply the −3 dB cutoff frequency at low frequency is 12 Hz. The source must be created. This can be accomplished with a simple values of C1, C2, C5, and C6 can be adjusted to change the low resistive voltage divider. Figure 60 shows the proper connection frequency −3 dB cutoff point to suit individual design needs. for terminating an unused amplifier in a single-supply For more information about single-supply operation of op amps, configuration. see the Analog Dialogue article “Avoiding Op Amp Instability +V S Problems in Single-Supply Applications” (Volume 35, Number 2) at www.analog.com. 2.5kΩ +5V C2 C3 2.5kΩ ADA4891 1µF 10µF R2 R4 C4 50kΩ 50kΩ 0.01µF +5V Figure 60. Terminating Unused Amplifier with Single Power Supply R3 100kΩ DISABLE FEATURE (ADA4891-3 ONLY) C6 V 22µF IN The ADA4891-3 includes a power-down feature that can be R1 C1 V OUT 50Ω 22µF R used to save power when an amplifier is not in use. When an L 150Ω amplifier is powered down, its output goes to a high impedance R F R G state. The output impedance decreases as frequency increases; 453Ω 453Ω ADA4891-3 this effect can be observed in Figure 34. With the power-down C5 22µF –V function, a forward isolation of −40 dB can be achieved at S 50 MHz. Figure 46 shows the forward isolation vs. frequency Figure 61. Single-Supply Video Driver Schematic PD1 data. The power-down feature is asserted by pulling the , PD2 PD3 , or pin low. Table 7 summarizes the operation of the power-down feature. Table 7. Disable Function Power-Down Pin Connection (PDx) Amplifier Status >V or floating Enabled TH