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EL2480CS-T13 Datasheet(PDF) 11 Page - Elantec Semiconductor |
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EL2480CS-T13 Datasheet(HTML) 11 Page - Elantec Semiconductor |
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11 / 17 page  11 EL2180C/EL2280C/EL2480C-Preliminary 250MHz / 3mA Current Mode Feedback Amplifiers Feedback Resistor Values The EL2180C/EL2280C/EL2480C have been designed and specified at gains of +1 and +2 with RF = 750Ω in PDIP and SO packages and RF = 560Ω in 5-pin SOT23 package. These values of feedback resistors give 250MHz of -3dB bandwidth at AV = +1 with about 2.5dB of peaking, and 180MHz of -3dB bandwidth at AV = +2 with about 0.1dB of peaking. The 5-pin SOT23 package is characterized with a smaller value of feed- back resistor, for a given bandwidth, to compensate for lower parasitics within both the package itself and the printed circuit board where it will be placed. Since the EL2180C/EL2280C/EL2480C are current-feedback amplifiers, it is also possible to change the value of RF to get more bandwidth. As seen in the curve of Frequency Response For Various RF and RG, bandwidth and peak- ing can be easily modified by varying the value of the feedback resistor. Because the EL2180C/EL2280C/EL2480C are current- feedback amplifiers, their gain-bandwidth product is not a constant for different closed-loop gains. This feature actually allows the EL2180C/EL2280C/EL2480C to maintain about the same -3dB bandwidth, regardless of closed-loop gain. However, as closed-loop gain is increased, bandwidth decreases slightly while stability increases. Since the loop stability is improving with higher closed-loop gains, it becomes possible to reduce the value of RF below the specified 560Ω and 750Ω and still retain stability, resulting in only a slight loss of bandwidth with increased closed-loop gain. Supply Voltage Range and Single-Supply Operation The EL2180C/EL2280C/EL2480C have been designed to operate with supply voltages having a span of greater than 3V, and less than 12V. In practical terms, this means that the EL2180C/EL2280C/EL2480C will oper- ate on dual supplies ranging from ±1.5V to ±6V. With a single-supply, the EL2180C/EL2280C/EL2480C will operate from +3V to +12V. As supply voltages continue to decrease, it becomes nec- essary to provide input and output voltage ranges that can get as close as possible to the supply voltages. The EL2180C/EL2280C/EL2480C have an input voltage range that extends to within 1V of either supply. So, for example, on a single +5V supply, the EL2180C/ EL2280C/EL2480C have an input range which spans from 1V to 4V. The output range of the EL2180C/EL2280C/EL2480C is also quite large, extending to within 1V of the supply rail. On a ±5V sup- ply, the output is therefore capable of swinging from---- -4V to +4V. Single-supply output range is even larger because of the increased negative swing due to the exter- nal pull-down resistor to ground. On a single +5V supply, output voltage range is about 0.3V to 4V. Video Performance For good video performance, an amplifier is required to maintain the same output impedance and the same fre- quency response as DC levels are changed at the output. This is especially difficult when driving a standard video load of 150 Ω, because of the change in output current with DC level. Until the EL2180C/EL2280C/EL2480C, good Differential Gain could only be achieved by run- ning high idle currents through the output transistors (to reduce variations in output impedance). These currents were typically comparable to the entire 3mA supply cur- rent of each EL2180C/EL2280C/EL2480C amplifier! Special circuitry has been incorporated in the EL2180C/EL2280C/EL2480C to reduce the variation of output impedance with current output. This results in dG and dP specifications of 0.05% and 0.05° while driving 150 Ω at a gain of +2. Video Performance has also been measured with a 500 Ω load at a gain of +1. Under these conditions, the EL2180C/EL2280C/EL2480C have dG and dP specifi- cations of 0.01% and 0.01° respectively while driving 500 Ω at AV = +1. Output Drive Capability In spite of its low 3mA of supply current, the EL2180C is capable of providing a minimum of ±80mA of output current. Similarly, each amplifier of the EL2280C and the EL2480C is capable of providing a minimum of ±50mA. These output drive levels are unprecedented in amplifiers running at these supply currents. With a min- imum ±80mA of output drive, the EL2180C is capable of driving 50 Ω loads to ±4V, making it an excellent choice for driving isolation transformers in telecommu- nications applications. Similarly, the ±50mA minimum |
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Similar Description - EL2480CS-T13 |
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