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EL2020CM Datasheet(PDF) 11 Page - Elantec Semiconductor |
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EL2020CM Datasheet(HTML) 11 Page - Elantec Semiconductor |
11 / 20 page EL2020C 50 MHz Current Feedback Amplifier Application Information Contd Summing Amplifier 2020 – 12 EL2020 Typical Inverting Amplifier Characteristics 10V AV RF R1 R2 Bandwidth Settling Time 1% 01% b 1 750 X 750 X 40 MHz 50 ns 130 ns b 2 750 X 375 X 40 MHz 55 ns 160 ns b 5 680 X 130 X 40 MHz 55 ns 160 ns b 10 680 X 68 X 30 MHz 70 ns 170 ns Input Range The non-inverting input to the EL2020 looks like a high resistance in parallel with a few picofarads in addition to a DC bias current The input char- acteristics change very little with output loading even when the amplifier is in current limit The input charactersitics also change when the input voltage exceeds either supply by 05V This happens because the input transistor’s base-col- lector junctions forward bias If the input exceeds the supply by LESS than 05V and then returns to the normal input range the output will recov- er in less than 10 ns However if the input ex- ceeds the supply by MORE than 05V the recov- ery time can be 100’s of nanoseconds For this reason it is recommended that Schottky diode clamps from input to supply be used if a fast re- covery from large input overloads is required Source Impedance The EL2020 is fairly tolerant of variations in source impedances Capacitive sources cause no problems at all resistive sources up to 100 k X present no problems as long as care is used in board layout to minimize output to input cou- pling Inductive sources may cause oscillations a 1k X resistor in series with the input lead will usually eliminate problems without sacrificing too much speed Current Limit The EL2020 has internal current limits that pro- tect the output transistors The current limit goes down with junction temperature rise At a junction temperature of a175 C the current lim- its are at about 50 mA If the EL2020 output is shorted to ground when operating on g15V sup- plies the power dissipation could be as great as 11W A heat sink is required in order for the EL2020 to survive an indefinite short Recovery time to come out of current limit is about 50 ns Using the 2020 with Output Buffers When more output current is required a wide- band buffer amplifier can be included in the feed- back loop of the EL2020 With the EL2003 the subsystem overshoots about 10% due to the phase lag of the EL2003 With the EL2004 in the loop the overshoot is less than 2% For even more output current several buffers can be paral- leled EL2020 Buffered with an EL2004 2020 – 13 Capacitive Loads The EL2020 is like most high speed feedback am- plifiers in that it does not like capacitive loads between 50 pF and 1000 pF The output resist- ance works with the capacitive load to form a second non-dominate pole in the loop This re- sults in excessive peaking and overshoot and can lead to oscillations Standard resistive isolation techniques used with other op amps work well to isolate capacitive loads from the EL2020 11 |
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