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| Single-Supply, High Speed, Fixed G = +2, Rail-to-Rail Output Video Amplifier ADA4856-3 FEATURES Voltage feedback architecture Rail-to-rail output swing: 0.1 V to 4.9 V High speed amplifier -3 dB bandwidth: 225 MHz 0.1 dB flatness at 2 V p-p: 74 MHz Slew rate: 800 V/s Settling time to 0.1% with 2 V step: 5 ns High input common-mode voltage range -VS - 0.2 V to +VS - 1 V Supply range: 3 V to 5.5 V Differential gain error: 0.01% Differential phase error: 0.01 Low power 7.8 mA/amplifier typical supply current Power-down feature Available in 16-lead LFCSP CONNECTION DIAGRAM OUT1 +IN1 -IN1 16 15 14 13 NC +IN2 NC PD 1 2 3 4 -VS 12 +VS 11 OUT2 ADA4856-3 10 -IN2 9 +VS 5 +IN3 6 -IN3 7 OUT3 8 -VS Figure 1. APPLICATIONS Professional video Consumer video Imaging Instrumentation Base stations Active filters Buffers GENERAL DESCRIPTION The ADA4856-3 (triple) is a fixed gain of +2, single-supply, railto-rail output video amplifier. It provides excellent video performance with 225 MHz, -3 dB bandwidth, 800 V/s slew rate, and 74 MHz, 0.1 dB flatness into a 150 load. It has a wide input common-mode voltage range that extends 0.2 V below ground and 1 V below the positive rail. In addition, the output voltage swings within 200 mV of either supply, making this video amplifier easy to use on single-supply voltages as low as 3.3 V. The ADA4856-3 offers a typical low power of 7.8 mA per amplifier, while being capable of delivering up to 52 mA of load current. It also features a power-down function for power sensitive applications that reduces the supply current to 1 mA. The ADA4856-3 is available in a 16-lead LFCSP and is designed to work over the extended industrial temperature range of -40C to +105C. CLOSED-LOOP GAIN (dB) 7 6 VS = 5V, VOUT = 1.4V p-p VS = 3.3V, VOUT = 1.4V p-p VS = 3.3V, VOUT = 2V p-p 5 4 3 2 1 0 1 RL = 150 10 100 FREQUENCY (MHz) VS = 5V, VOUT = 2V p-p 07686-001 NOTES 1. NC = NO CONNECT. 2. EXPOSED PAD CONNECTED TO -VS. 1000 Figure 2. Large Signal Frequency Response 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. 07686-058 ADA4856-3 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Connection Diagram ....................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 5 V Operation ............................................................................... 3 3.3 V Operation ............................................................................ 4 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 ...................................................................... 12 Applications Information .............................................................. 13 Using the ADA4856-3 in Gains Equal to +1, -1........................ 13 Using the ADA4856-3 in Gains Equal to +3, +4, and +5 ..... 14 20 MHz Active Low-Pass Filter ................................................ 15 Video Line Driver ....................................................................... 15 Single-Supply Operation ........................................................... 16 Power Down ................................................................................ 16 Layout Considerations ............................................................... 16 Power Supply Bypassing ............................................................ 16 Outline Dimensions ....................................................................... 17 Ordering Guide .......................................................................... 17 REVISION HISTORY 10/08--Revision 0: Initial Version Rev. 0 | Page 2 of 20 ADA4856-3 SPECIFICATIONS 5 V OPERATION TA = 25C, +VS = 5 V, -VS = 0 V, G = +2, RL = 150 to midsupply, unless otherwise noted. Table 1. Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Test Conditions VO = 0.1 V p-p VO = 1.4 V p-p VO = 2 V p-p VO = 1.4 V p-p VO = 2 V p-p VO = 2 V step VO = 2 V step fC = 5 MHz, VO = 2 V p-p, RL = 1 k fC = 20 MHz, VO = 2 V p-p, RL = 1 k f = 5 MHz, G = +2 f = 100 kHz f = 100 kHz Min Typ 370 225 200 90 74 800 4.8/5.2 -92/-110 -68/-71 -80 14 2 0.01 0.01 1.3 5.5 -3.8 0.05 2 90 3.2 0.5 -VS - 0.2 VCM = -0.2 V to +4 V 94 0.1 to 4.9 52 78 950 0.2 -125 3.75 3 7.8 1.1 96 5.5 +VS - 1 3.4 Max Unit MHz MHz MHz MHz MHz V/s ns dBc dBc dBc nV/Hz pA/Hz % Degrees mV V/C A A V/V dB M pF V dB V mA ns ns A A V V mA mA dB Bandwidth for 0.1 dB Flatness Slew Rate Settling Time to 0.1% (Rise/Fall) NOISE/DISTORTION PERFORMANCE Harmonic Distortion (HD2/HD3) Crosstalk, Output to Output Input Voltage Noise Input Current Noise Differential Gain Error Differential Phase Error DC PERFORMANCE Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Offset Current Closed-Loop Gain Open-Loop Gain INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Output Voltage Swing Linear Output Current Per Amplifier POWER-DOWN Turn-On Time Turn-Off Time Input Bias Current Turn-On Voltage POWER SUPPLY Operating Range Quiescent Current per Amplifier Supply Current When Disabled Power Supply Rejection Ratio 1.95 2.05 HD2 -60 dBc, RL = 10 Enabled Powered down VS = 4.5 V to 5.5 V Rev. 0 | Page 3 of 20 ADA4856-3 3.3 V OPERATION TA = 25C, +VS = 3.3 V, -VS = 0 V, G = +2, RL = 150 to midsupply, unless otherwise noted. Table 2. Parameter DYNAMIC PERFORMANCE -3 dB Bandwidth Bandwidth for 0.1 dB Flatness Slew Rate Settling Time to 0.1% (Rise/Fall) NOISE/DISTORTION PERFORMANCE Harmonic Distortion (HD2/HD3) Crosstalk, Output to Output Input Voltage Noise Input Current Noise Differential Gain Error Differential Phase Error DC PERFORMANCE Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Offset Current Closed-Loop Gain Open-Loop Gain INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Output Voltage Swing, Load Resistance Linear Output Current Per Amplifier POWER-DOWN Turn-On Time Turn-Off Time Turn-On Voltage POWER SUPPLY Operating Range Quiescent Current per Amplifier Quiescent Current When Powered Down Power Supply Rejection Ratio Test Conditions VO = 0.1 V p-p VO = 2 V p-p VO = 2 V p-p VO = 2 V step VO = 2 V step fC = 5 MHz, VO = 2 V p-p, RL = 1 k fC = 20 MHz, VO = 2 V p-p, RL = 1 k f = 5 MHz, G = +2 f = 100 kHz f = 100 kHz Min Typ 370 225 77 800 4.8/7 -95/-128 -74/-101 -78 14 2 0.01 0.01 1.2 5.5 -3.8 0.05 2 90 3.2 0.5 -VS - 0.2 VCM = -0.2 V to +2.3 V 94 0.1 to 3.22 49 78 950 2.05 3 7.5 0.98 94 5.5 +VS - 1 3 Max Unit MHz MHz MHz V/s ns dBc dBc dBc nV/Hz pA/Hz % Degrees mV V/C A A V/V dB M pF V dB V mA ns ns V V mA mA dB 1.95 2.05 HD2 -60 dBc, RL = 10 VS = 2.97 V to 3.63 V Rev. 0 | Page 4 of 20 ADA4856-3 ABSOLUTE MAXIMUM RATINGS Table 3. Parameter Supply Voltage Internal Power Dissipation1 Common-Mode Input Voltage Differential Input Voltage Output Short-Circuit Duration Storage Temperature Range Operating Temperature Range Lead Temperature (Soldering, 10 sec) 1 MAXIMUM POWER DISSIPATION Rating 6V See Figure 3 (-VS - 0.2 V) to (+VS - 1 V) VS Observe power curves -65C to +125C -40C to +105C 300C The maximum power that can be safely dissipated by the ADA4856-3 is limited by the associated rise in junction temperature. The maximum safe junction temperature for plastic encapsulated devices is determined by the glass transition temperature of the plastic, approximately 150C. Temporarily exceeding this limit may cause a shift in parametric performance due to a change in the stresses exerted on the die by the package. Exceeding a junction temperature of 175C for an extended period can result in device failure. To ensure proper operation, it is necessary to observe the maximum power derating curves. 3.0 MAXIMUM POWER DISSIPATION (W) Specification is for device in free air. 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. 2.5 2.0 1.5 THERMAL RESISTANCE JA is specified for the worst-case conditions, that is, JA is specified for a device soldered in a circuit board for surface-mount packages. Table 4. Package Type 16-Lead LFCSP JA 67 JC 17.5 Unit C/W 1.0 0.5 07686-103 0 10 20 30 40 50 60 70 80 -40 -30 -20 -10 90 AMBIENT TEMPERATURE (C) Figure 3. Maximum Power Dissipation vs. Ambient Temperature ESD CAUTION Rev. 0 | Page 5 of 20 100 0 ADA4856-3 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS OUT1 +IN1 -IN1 -VS 16 15 14 13 NC +IN2 NC PD 1 2 3 4 12 +VS ADA4856-3 TOP VIEW (Not to Scale) 11 OUT2 10 -IN2 9 +VS 5 +IN3 6 -IN3 7 OUT3 8 -VS Figure 4. Pin Configuration Table 5. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 (EPAD) Mnemonic NC +IN2 NC PD +IN3 -IN3 OUT3 -VS +VS -IN2 OUT2 +VS -VS OUT1 -IN1 +IN1 Exposed Pad (EPAD) Description No Connect. Noninverting Input 2. No Connect. Power Down. Noninverting Input 3. Inverting Input 3. Output 3. Negative Supply. Positive Supply. Inverting Input 2. Output 2. Positive Supply. Negative Supply. Output 1. Inverting Input 1. Noninverting Input 1. The exposed pad must be connected to -VS. Rev. 0 | Page 6 of 20 07686-003 NOTES 1. NC = NO CONNECT. 2. EXPOSED PAD CONNECTED TO -VS. ADA4856-3 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, +VS = 5 V, G = +2, RL = 150 , large signal VOUT = 2 V p-p, small signal VOUT = 100 mV p-p, unless otherwise noted. 7 VS = 3.3V 6 CLOSED-LOOP GAIN (dB) CLOSED-LOOP GAIN (dB) 6 7 VS = 5V, VOUT = 1.4V p-p VS = 3.3V, VOUT = 1.4V p-p 5 4 3 2 1 0 VS = 5V VS = 3.3V, VOUT = 2V p-p 5 4 3 2 1 0 1 10 100 FREQUENCY (MHz) VS = 5V, VOUT = 2V p-p 1 10 100 FREQUENCY (MHz) 1000 1000 Figure 5. Small Signal Frequency Response vs. Supply Voltage 6.2 Figure 8. Large Signal Frequency Response vs. Supply Voltage 2 TA = +105C 0 CLOSED-LOOP GAIN (dB) TA = +25C CLOSED-LOOP GAIN (dB) 6.1 VS = 3.3V, VOUT = 1.4V p-p VS = 5V, VOUT = 1.4V p-p 6.0 VS = 3.3V, VOUT = 2V p-p VS = 5V, VOUT = 2V p-p 5.9 07686-006 -2 TA = +25C TA = +85C TA = +105C TA = -40C TA = -40C TA = +85C -4 -6 07686-009 5.8 1 10 100 FREQUENCY (MHz) 1000 -8 1M 10M 100M FREQUENCY (Hz) 1G Figure 6. Large Signal 0.1 dB Flatness vs. Supply Voltage 7 Figure 9. Small Signal Frequency Response vs. Temperature CL = 4.4pF 6 6 RL = 1k RL = 150 CLOSED-LOOP GAIN (dB) 4 CL = 6.6pF CL = 2.2pF CLOSED-LOOP GAIN (dB) 5 4 3 2 1 0 2 0 -2 07686-007 -6 1 10 100 FREQUENCY (MHz) 1 10 100 FREQUENCY (MHz) 1000 1000 Figure 7. Small Signal Frequency Response vs. Load Resistance Figure 10. Small Signal Frequency Response vs. Capacitive Load Rev. 0 | Page 7 of 20 07686-010 -4 07686-008 07686-005 ADA4856-3 -50 -60 -70 -80 -90 -100 HD2 -110 -120 07686-011 -50 RL = 1k VOUT = 2V p-p -60 -70 DISTORTION (dBc) RL = 1k VOUT = 1V p-p VS = 3.3V DISTORTION (dBc) -80 -90 -100 -110 HD2 -120 07686-014 HD3 HD3 -130 -140 0.1 1 10 FREQUENCY (MHz) -130 -140 0.1 1 10 FREQUENCY (MHz) 100 100 Figure 11. Harmonic Distortion vs. Frequency 0 -10 -20 Figure 14. Harmonic Distortion vs. Frequency ALL HOSTILE CROSSTALK (dB) -20 FORWARD ISOLATION (dB) -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 1M 10M FREQUENCY (Hz) 100M 07686-015 IN1, IN3, OUT2 -40 OUT3 OUT1 -60 IN1, IN2, OUT3 IN2, IN3, OUT1 -80 OUT2 -100 07686-012 -120 0.1 1 10 FREQUENCY (MHz) 100 1000 Figure 12. Forward Isolation vs. Frequency 0 -10 -20 SETTLING TIME (%) Figure 15. Crosstalk vs. Frequency 0.5 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 07686-013 -30 PSRR (dB) -40 -50 -60 -70 -80 -90 -100 0.01 0.1 1 10 100 +PSRR -PSRR -0.4 -0.5 TIME (2ns/DIV) FREQUENCY (MHz) Figure 13. Power Supply Rejection Ratio (PSRR) vs. Frequency Figure 16. Settling Time Rev. 0 | Page 8 of 20 07685-024 ADA4856-3 1k 25.0 QUIESCENT CURRENT (mA) VOLTAGE NOISE (nV/Hz) VS = 5V 24.5 24.0 100 23.5 23.0 22.5 07686-017 07686-057 10 100 22.0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 SUPPLY VOLTAGE (V) 1k 10k FREQUENCY (Hz) 100k 1M Figure 17. Output Voltage Noise vs. Frequency 0.06 VS = 5V VS = 3.3V 1.5 Figure 20. Quiescent Current vs. Supply Voltage 0.04 OUTPUT VOLTAGE (V) 1.0 OUTPUT VOLTAGE (V) VS = 5V VS = 3.3V 0.02 0.5 0 0 -0.02 -0.5 -0.04 07686-018 -1.0 07686-021 -0.06 TIME (10ns/DIV) -1.5 TIME (10ns/DIV) Figure 18. Small Signal Transient Response vs. Supply Voltage 0.08 0.06 0.04 0.02 0 -0.02 -0.04 07686-019 Figure 21. Large Signal Transient Response vs. Supply Voltage 1.5 1.0 CL = 2.2pF CL = 4.4pF CL = 6.6pF OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 0.5 CL = 2.2pF CL = 4.4pF CL = 6.6pF 0 -0.5 -1.0 07686-022 -0.06 -0.08 TIME (10ns/DIV) -1.5 TIME (10ns/DIV) Figure 19. Small Signal Transient Response vs. Capacitive Load Figure 22. Large Signal Transient Response vs. Capacitive Load Rev. 0 | Page 9 of 20 ADA4856-3 0.08 0.06 0.04 0.02 0 -0.02 -0.04 07686-023 1.5 1.0 CL = 2.2pF CL = 4.4pF CL = 6.6pF OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 0.5 CL = 2.2pF CL = 4.4pF CL = 6.6pF 0 -0.5 -1.0 VS = 3.3V -0.08 TIME (10ns/DIV) VS = 3.3V -1.5 TIME (10ns/DIV) 07686-026 -0.06 Figure 23. Small Signal Transient Response vs. Capacitive Load 4 3 2 VOLTAGE (V) Figure 26. Large Signal Transient Response vs. Capacitive Load 2.5 2 x VIN 2.0 1.5 2 x VIN VOUT VOLTAGE (V) 1.0 0.5 0 -0.5 -1.0 VOUT 1 0 -1 -2 -1.5 07686-025 -2.0 -2.5 VS = 3.3V -4 TIME (50ns/DIV) TIME (50ns/DIV) Figure 24. Output Overdrive Recovery 3.0 2.5 2.0 1.5 VOLTAGE (V) Figure 27. Output Overdrive Recovery 23.6 VPD 23.4 QUIESCENT CURRENT (mA) 23.2 23.0 22.8 22.6 22.4 22.2 22.0 VS = 5V 1.0 0.5 0 -0.5 VOUT VS = 3.3V -25 -10 5 20 35 50 65 80 95 110 125 TIME (1us/DIV) TEMPERATURE (C) Figure 25. Turn-On/Turn-Off Time Figure 28. Quiescent Current vs. Temperature Rev. 0 | Page 10 of 20 07686-132 -1.5 07686-056 -1.0 21.8 -40 07686-028 -3 ADA4856-3 1.8 1.7 SATURATION VOLTAGE (mV) 1.6 OFFSET VOLTAGE (mV) 5.00 4.95 4.90 4.85 4.80 4.75 4.70 07686-038 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 -40 -20 0 20 40 60 80 100 120 07686-034 4.65 4.60 0.01 0.1 1 LOAD CURRENT (mA) 10 100 TEMPERATURE (C) Figure 29. Offset Drift vs. Temperature 100 Figure 31. Output Saturation Voltage vs. Load Current OUTPUT IMPEDENCE () 10 1 0.1 07686-135 0.01 100k 1M 10M 100M FREQUENCY (Hz) 1G Figure 30. Output Impedance vs. Frequency Rev. 0 | Page 11 of 20 ADA4856-3 THEORY OF OPERATION The ADA4856-3 is a voltage feedback op amp that employs a new input stage that achieves a high slew rate while maintaining a wide common-mode input range. The input common-mode range of the ADA4856-3 extends from 200 mV below the negative rail to about 1 V from the positive rail. This feature makes the ADA4856-3 ideal for low voltage single-supply applications. In addition, this new input stage does not sacrifice noise performance for slew rate. At 14 nV/Hz, the ADA4856-3 is one of the lowest noise rail-to-rail output video amplifiers in the market. Besides a novel input stage, the ADA4856-3 employs the Analog Devices, Inc., patented rail-to-rail output stage. This output stage makes an efficient use of the power supplies, allowing the op amp to drive up to three video loads to within 300 mV from both rails. In addition, this output stage provides the amplifier with very fast overdrive characteristics, an important property in video applications. The ADA4856-3 comes in a 16-lead LFCSP that has an exposed thermal pad for lower operating temperature. This pad is connected internally to the negative rail. To avoid printed circuit board (PCB) layout problems, the ADA4856-3 features a new pinout flow that is optimized for video applications. As shown in Figure 4, the feedback and gain resistors are on-chip, which minimizes the number of components needed and improves the design layout. The ADA4856-3 is fabricated in Analog Devices dielectrically isolated eXtra Fast Complementary Bipolar 3 (XFCB3) process, which results in the outstanding speed and dynamic range displayed by the amplifier. +VS C1 +IN Gm1 -IN R Gm2 OUT -VS Figure 32. High Level Design Schematic Rev. 0 | Page 12 of 20 07686-147 C ADA4856-3 APPLICATIONS INFORMATION USING THE ADA4856-3 IN GAINS EQUAL TO +1, -1 The ADA4856-3 was designed to offer outstanding video performance, simplify applications, and minimize board area. The ADA4856-3 is a triple amplifier with on-chip feedback and gain set resistors. The gain is fixed internally at G = +2. The inclusion of the on-chip resistors not only simplifies the design of the application but also eliminates six surface-mount resistors, saving valuable board space and lowering assembly costs. Whereas the ADA4856-3 has a fixed gain of G = +2, it can be used in other gain configurations, such as G = -1 and G = +1. RF RG VIN RT 0.1F VOUT +VS 10F 0.1F 10F -VS GAIN OF +1 07686-030 Unity-Gain Operation Option 1 There are two options for obtaining unity gain (G = +1). The first is shown in Figure 33. In this configuration, the -IN input pin is tied to the output (feedback is now provided with the two internal 402 resistors in parallel), and the input is applied to the noninverting input. The noise gain for this configuration is 1. +VS 10F Figure 34. Unity Gain of Option 2 Inverting Unity-Gain Operation In this configuration, the noninverting input is tied to ground and the input signal is applied to the inverting input. The noise gain for this configuration is +2, see Figure 35. +VS 10F 0.1F 0.1F VIN VIN RT 0.1F 07686-032 VOUT RT 0.1F VOUT -VS GAIN OF +1 GAIN OF -1 Figure 33. Unity Gain of Option 1 Figure 35. Inverting Configuration (G = -1) Option 2 Another option exists for running the ADA4856-3 as a unitygain amplifier. In this configuration, the noise gain is +2, see Figure 34. The frequency response and transient response for this configuration closely match the gain of +2 plots because the noise gains are equal. This method does have twice the noise gain of Option 1; however, in applications that do not require low noise, Option 2 offers less peaking and ringing. By tying the inputs together, the net gain of the amplifier becomes 1. Equation 1 shows the transfer characteristic for the schematic shown in Figure 34. Figure 36 shows the small signal frequency response for both gain of +1 (Option 1 and Option 2) and gain of -1 configurations. It is clear that G = +1, Option 2 has better flatness and no peaking compared to Option 1. 6 VS = 5V RL = 100 VOUT = 100mV p-p OPTION 1 G = +1 3 MAGNITUDE (dB) 0 G = -1 OPTION 2 G = +1 -3 - RF VOUT = V IN R G R + RG + V IN F R G (1) -6 which simplifies to VOUT = VIN. -9 07686-044 -12 1 10 100 FREQUENCY (MHz) 07686-031 10F -VS 10F 1000 Figure 36. G = +1 and G = -1 Rev. 0 | Page 13 of 20 ADA4856-3 USING THE ADA4856-3 IN GAINS EQUAL TO +3, +4, AND +5 Depending on certain applications, it might be useful to have a fixed gain amplifier that can provide various gains. The advantage of having a fixed gain amplifier is the ease of layout, the reduced number of components needed, and the matching of the gain and feedback resistors. As shown in Figure 40, the large signal frequency response for G = +4 is also flat out to 65 MHz, and it has a bandwidth of 180 MHz. Gain of+ 5 Configuration The gain of +5 is very similar to the G = +3 configuration but with U2 set to a gain of -1, which ends up being added to twice the output of U1 to generate VOUT with G = +5. -VS 10F Gain of +3 Configuration Figure 37 shows the ADA4856-3 used as an amplifier with a fixed gain of +3. No external resistors are required, just a simple trace connecting certain inputs and outputs. Connect VIN to U1, which is set to a gain of +2, and U2, which is set to unity. U3 then takes the output of U1 and gains it up by +2 and subtracts the output of U2 to produce VOUT. As shown in Figure 40, the large signal frequency response for G = +3 is flat out to 65 MHz, with a bandwidth of 165 MHz, a 2 V p-p output voltage, and a 100 load. -VS 5 6 7 16 15 14 13 0.1F 1 12 11 VIN +VS VOUT 2 3 ADA4856-3 10 9 PD 4 +VS + 0.1F 10F 07686-047 8 16 15 14 13 0.1F 1 12 11 VIN +VS VOUT 2 3 ADA4856-3 10 9 PD 4 +VS + 0.1F 07686-045 5 6 7 8 10F CLOSED-LOOP GAIN (dB) 0.1F -VS Figure 37. Gain of +3 Gain of +4 Configuration To get a gain of +4, set one amplifier to a gain of +1 and set the other two amplifiers to a gain of +2. Figure 38 shows VIN going in U2 at unity, then U1 takes the output of U2 and gains it by +2, and then feeds it to U3, which also gains it by +2 to produce VOUT. -VS 10F -15 -18 1 10 100 1000 16 15 14 13 0.1F 1 2 3 12 11 +VS VOUT ADA4856-3 10 9 PD 4 +VS + 0.1F 10F 07686-046 5 6 7 8 VIN -VS 0.1F Figure 38. Gain of +4 + 0.1F FREQUENCY (MHz) Figure 40. Large Signal Frequency Response for All Three Gains Rev. 0 | Page 14 of 20 07686-048 + 0.1F 10F -VS 0.1F Figure 39. Gain of +5 Figure 40 shows the large signal frequency response of the three closed-loop gain sets (+3, +4, and +5) with flatness that extends to 65 MHz and a -3 dB bandwidth of 150 MHz. 15 12 9 6 3 0 -3 -6 -9 -12 RL = 100 VS = 5V VOUT = 2V p-p G = +3 G = +4 G = +5 + 0.1F ADA4856-3 20 MHz ACTIVE LOW-PASS FILTER The ADA4856-3 triple amplifier lends itself to higher order active filters. Figure 41 shows a 20 MHz, 6-pole, Sallen-Key low-pass filter. - R1 93.1 R2 604 C1 33pF C2 22pF 1 12 VIDEO LINE DRIVER The ADA4856-3 was designed to excel in video driver applications. Figure 43 shows a typical schematic for a video driver operating on bipolar supplies. 75 VIN (R) 75 16 15 14 VOUT (R) 13 0.1F +VS 75 VIN (G) 75 2 3 ADA4856-3 11 10 9 - R3 113 R4 732 C3 33pF C4 15pF U2 OP AMP + OUT2 PD 4 +VS 0.1F 0.1F + 5 6 7 8 VIN (B) 75 -VS 75 0.1F 07686-051 VOUT (B) Figure 43. Video Driver Schematic - R5 121 R6 475 C5 47pF C6 15pF U3 OP AMP + OUT3 VOUT 07686-049 In applications that require multiple video loads be driven simultaneously, the ADA4856-3 can deliver. Figure 44 shows the ADA4856-3 configured with triple video loads. Figure 45 shows the triple video load performance. +VS 10F 0.1F 75 75 CABLE VOUT1 75 75 75 CABLE 0.1F 0.1F 75 10F 75 CABLE VOUT3 75 07686-052 07686-053 Figure 41. 20 MHz, 6-Pole Low-Pass Filter The filter has a gain of approximately 18 dB, which is set by three fixed gain of 2 stages, and a flat frequency response out to 14 MHz. This type of filter is commonly used at the output of a video DAC as a reconstruction filter. The frequency response of the filter is shown in Figure 42. 20 SIX POLES 10 0 MAGNITUDE (dB) VIN - ADA4856-3 + 75 CABLE 75 FOUR POLES TWO POLES -VS Figure 44. Video Driver Schematic for Triple Video Loads 6.5 -10 6.0 -20 5.5 -30 MAGNITUDE (dB) 5.0 4.5 4.0 3.5 3.0 2.5 1 RL = 150 RL = 75 RL = 50 -40 07686-050 -50 -60 1 10 FREQUENCY (MHz) 100 200 Figure 42. 20 MHz, Low-Pass Filter Frequency Response VS = 5V VOUT = 1V p-p 10 FREQUENCY (MHz) 100 Figure 45. Large Signal Frequency Response for Various Loads Rev. 0 | Page 15 of 20 + VIN U1 OP AMP + OUT1 -VS 0.1F 10F 0.1F VOUT (G) 10F VOUT2 75 200 ADA4856-3 SINGLE-SUPPLY OPERATION The ADA4856-3 can operate in single-supply applications. Figure 46 shows the schematic for a single 5 V supply video driver. Resistors R2 and R4 establish the midsupply reference. Capacitor C2 is the bypass capacitor for the midsupply reference. Capacitor C1 is the input coupling capacitor, and C6 is the output coupling capacitor. Capacitor C5 prevents constant current from being drawn through the internal gain set resistor. Resistor R3 sets the ac input impedance of the circuit. For more information on single-supply operation of op amps, see "Avoiding Op-Amp Instability Problems In Single-Supply Applications", Analog Dialogue, Volume 35, Number 2, MarchMay, 2001, at www.analog.com. +5V C2 1F C3 2.2F POWER DOWN The ADA4856-3 is equipped with a PD (power-down) pin for all three amplifiers. This allows the user to reduce the quiescent supply current when an amplifier is inactive. The power-down threshold levels are derived from the voltage applied to the +VS pin. When used in single-supply applications, this is especially useful with conventional logic levels. The amplifier is enabled when the voltage applied to the PD pin is greater than +VS - 1.25 V. In a 5 V single-supply application, the typical threshold voltage is +3.75 V, and in a 3.3 V dual-supply application, the typical threshold voltage is +2 V. The amplifier is also enabled when the PD pin is left floating (not connected). However, the amplifier is powered down when the voltage on the PD pin is lower than 2.5 V from +VS. If the PD pin is not used, it is best to connect it to the positive supply Table 6. Power-Down Voltage Control PD Pin C6 220F R5 75 VOUT R6 75 +5V R2 50k R3 1k R4 50k C4 0.01F 5V >3.75 V <2 V 2.5 V >1.25 V <0 V 3.3 V >2.05 V <1.3 V VIN R1 50 C1 22F Not Active Active LAYOUT CONSIDERATIONS As is the case with all high speed applications, careful attention to printed circuit board (PCB) layout details prevents associated board parasitics from becoming problematic. Proper RF design technique is mandatory. The PCB should have a ground plane covering all unused portions of the component side of the board to provide a low impedance return path. Removing the ground plane on all layers from the area near the input and output pins reduces stray capacitance. Locate termination resistors and loads as close as possible to their respective inputs and outputs. Keep input and output traces as far apart as possible to minimize coupling (crosstalk) though the board. Adherence to microstrip or stripline design techniques for long signal traces (greater than about 1 inch) is recommended. ADA4856-3 -VS 07686-035 C5 22F Figure 46. AC-Coupled, Single-Supply Video Driver Schematic In addition, the ADA4856-3 can be configured in dc-coupled, single-supply operation. The common-mode input voltage can go about 200 mV below ground, which makes it a true singlesupply part. However, in video applications, the black level is set at 0 V, which means that the output of the amplifier must go to the ground level as well. This part has a rail-to-rail output stage; it can go as close as 100 mV from either rail. Figure 47 shows the schematic for adding 50 mV dc offset to the input signal so that the output is not clipped while still properly terminating the input with 75 . C1 10F 5V R1 3.74k VIN R2 76.8 U1 R3 75 VOUT R4 75 5V C2 0.1F POWER SUPPLY BYPASSING Careful attention must be paid to bypassing the power supply pins of the ADA4856-3. Use high quality capacitors with low equivalent series resistance (ESR), such as multilayer ceramic capacitors (MLCCs), to minimize supply voltage ripple and power dissipation. A large, usually tantalum, 10 F to 47 F capacitor located in proximity to the ADA4856-3 is required to provide good decoupling for lower frequency signals. In addition, locate 0.1 F MLCC decoupling capacitors as close to each of the power supply pins as is physically possible, no more than 1/8 inch away. The ground returns should terminate immediately into the ground plane. Locating the bypass capacitor return close to the load return minimizes ground loops and improves performance. Figure 47. DC-Coupled Single Supply Video Driver Schematic 07686-156 -VS ADA4856-3 Rev. 0 | Page 16 of 20 ADA4856-3 OUTLINE DIMENSIONS 4.00 BSC SQ 0.60 MAX 0.60 MAX 0.65 BSC 3.75 BSC SQ 0.75 0.60 0.50 (BOTTOM VIEW) PIN 1 INDICATOR 13 12 16 PIN 1 INDICATOR 1 TOP VIEW 2.25 2.10 SQ 1.95 5 4 9 8 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 SEATING PLANE 0.35 0.30 0.25 0.20 REF COPLANARITY 0.08 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 072808-A COMPLIANT TO JEDEC STANDARDS MO-220-VGGC Figure 48.16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm x 4 mm Body, Very Thin Quad (CP-16-4) Dimensions shown in millimeters ORDERING GUIDE Model ADA4856-3YCPZ-R2 1 ADA4856-3YCPZ-R71 ADA4856-3YCPZ-RL1 1 Temperature Range -40C to +105C -40C to +105C -40C to +105C Package Description 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ 16-Lead LFCSP_VQ Package Option CP-16-4 CP-16-4 CP-16-4 Ordering Quantity 250 1,500 5,000 Z = RoHS Compliant Part. Rev. 0 | Page 17 of 20 ADA4856-3 NOTES Rev. 0 | Page 18 of 20 ADA4856-3 NOTES Rev. 0 | Page 19 of 20 ADA4856-3 NOTES (c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07686-0-10/08(0) Rev. 0 | Page 20 of 20 |
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