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EL5364IU-T7 Datasheet(PDF) 10 Page - Intersil Corporation |
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EL5364IU-T7 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 12 page 10 FN7389.5 August 10, 2005 acceptable with the Metal-Film resistors giving slightly less peaking and bandwidth because of additional series inductance. Use of sockets, particularly for the SO package, should be avoided if possible. Sockets add parasitic inductance and capacitance which will result in additional peaking and overshoot. Disable/Power-Down The EL5164 amplifier can be disabled placing its output in a high impedance state. When disabled, the amplifier supply current is reduced to < 150µA. The EL5164 is disabled when its CE pin is pulled up to within 1V of the positive supply. Similarly, the amplifier is enabled by floating or pulling its CE pin to at least 3V below the positive supply. For ±5V supply, this means that an EL5164 amplifier will be enabled when CE is 2V or less, and disabled when CE is above 4V. Although the logic levels are not standard TTL, this choice of logic voltages allows the EL5164 to be enabled by tying CE to ground, even in 5V single supply applications. The CE pin can be driven from CMOS outputs. Capacitance at the Inverting Input Any manufacturer’s high-speed voltage- or current-feedback amplifier can be affected by stray capacitance at the inverting input. For inverting gains, this parasitic capacitance has little effect because the inverting input is a virtual ground, but for non-inverting gains, this capacitance (in conjunction with the feedback and gain resistors) creates a pole in the feedback path of the amplifier. This pole, if low enough in frequency, has the same destabilizing effect as a zero in the forward open-loop response. The use of large- value feedback and gain resistors exacerbates the problem by further lowering the pole frequency (increasing the possibility of oscillation.) The EL5164, EL5165, and EL5364 have been optimized with a TBD Ω feedback resistor. With the high bandwidth of these amplifiers, these resistor values might cause stability problems when combined with parasitic capacitance, thus ground plane is not recommended around the inverting input pin of the amplifier. Feedback Resistor Values The EL5164, EL5165, and EL5364 have been designed and specified at a gain of +2 with RF approximately 412Ω. This value of feedback resistor gives 300MHz of -3dB bandwidth at AV = 2 with 2dB of peaking. With AV = -2, an RF of 300Ω gives 275MHz of bandwidth with 1dB of peaking. Since the EL5164, EL5165, and EL5364 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 peaking can be easily modified by varying the value of the feedback resistor. Because the EL5164, EL5165, and EL5364 are current- feedback amplifiers, their gain-bandwidth product is not a constant for different closed-loop gains. This feature actually allows the EL5164, EL5165, and EL5364 to maintain about the same -3dB bandwidth. As 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 TBD Ω 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 EL5164, EL5165, and EL5364 have been designed to operate with supply voltages having a span of greater than 5V and less than 10V. In practical terms, this means that they will operate on dual supplies ranging from ±2.5V to ±5V. With single-supply, the EL5164, EL5165, and EL5364 will operate from 5V to 10V. As supply voltages continue to decrease, it becomes necessary to provide input and output voltage ranges that can get as close as possible to the supply voltages. The EL5164, EL5165, and EL5364 have an input range which extends to within 2V of either supply. So, for example, on ±5V supplies, the EL5164, EL5165, and EL5364 have an input range which spans ±3V. The output range of the EL5164, EL5165, and EL5364 is also quite large, extending to within 1V of the supply rail. On a ±5V supply, the output is therefore capable of swinging from -4V to +4V. Single-supply output range is larger because of the increased negative swing due to the external pull-down resistor to ground. Video Performance For good video performance, an amplifier is required to maintain the same output impedance and the same frequency 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. Previously, good differential gain could only be achieved by running high idle currents through the output transistors (to reduce variations in output impedance.) These currents were typically comparable to the entire 5.5mA supply current of each EL5164, EL5165, and EL5364 amplifiers. Special circuitry has been incorporated in the EL5164, EL5165, and EL5364 to reduce the variation of output impedance with current output. This results in dG and dP specifications of TBD% and TBD°, 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 EL5164, EL5165, and EL5364 have dG and dP specifications of 0.01% and 0.01°, respectively. Output Drive Capability In spite of their low 5.5mA of supply current, the EL5164, EL5165, and EL5364 are capable of providing a minimum of ±75mA of output current. With a minimum of ±75mA of output drive, the EL5164, EL5165, and EL5364 are capable of driving 50 Ω loads to both rails, making it an excellent EL5164, EL5165, EL5364 |
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