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HFA1150 Fiches technique(PDF) 4 Page - Intersil Corporation |
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HFA1150 Fiches technique(HTML) 4 Page - Intersil Corporation |
4 / 13 page 4 Application Information Relevant Application Notes The following Application Notes pertain to the HFA1150: • AN9787 - An Intuitive Approach to Understanding Current Feedback Amplifiers • AN9420 - Current Feedback Amplifier Theory and Applications • AN9663-Converting from Voltage Feedback to Current Feedback Amplifiers • AN9891-Operating the HFA1150 from 5V Single Supply These publications may be obtained from Intersil’s web site (http://www.intersil.com) or via our AnswerFAX system. Performance Differences Between Packages The HFA1150 is a high frequency current feedback amplifier. As such, it is sensitive to parasitic capacitances which influence the amplifier’s operation. The different parasitic capacitances of the SOIC and SOT-23 packages yield performance differences (notably bandwidth and bandwidth related parameters) between the two devices - see Electrical Specification tables for details. Because of these performance differences, designers should evaluate and breadboard with the same package style to be used in production. Note that some “Typical Performance Curves” have separate graphs for each package type. Graphs not labeled with a specific package type are applicable to both packages. Optimum Feedback Resistor The enclosed frequency response graphs detail the performance of the HFA1150 in various gains. Although the bandwidth dependency on ACL isn’t as severe as that of a voltage feedback amplifier, there is an appreciable decrease in bandwidth at higher gains. This decrease can be minimized by taking advantage of the current feedback amplifier’s unique relationship between bandwidth and RF. All current feedback amplifiers require a feedback resistor, even for unity gain applications, and the RF, in conjunction with the internal compensation capacitor, sets the dominant pole of the frequency response. Thus, the amplifier’s bandwidth is inversely proportional to RF. The HFA1150 is optimized for a RF = 576Ω/499Ω (SOIC/SOT-23), at a gain of +2. Decreasing RF decreases stability, resulting in excessive peaking and overshoot (Note: Capacitive feedback causes the same problems due to the feedback impedance decrease at higher frequencies). At higher gains the amplifier is more stable, so RF can be decreased in a trade- off of stability for bandwidth. The table below lists recommended RF values for various gains, and the expected bandwidth. 5V Single Supply Operation This amplifier operates at single supply voltages down to 4.5V. The dramatic supply current reduction at this operating condition (refer also to Figure 25) makes this op amp an even better choice for low power 5V systems. Refer to Application Note AN9891 for further information. Driving Capacitive Loads Capacitive loads, such as an A/D input, or an improperly terminated transmission line will degrade the amplifier’s phase margin resulting in frequency response peaking and possible oscillations. In most cases, the oscillation can be avoided by placing a resistor (RS) in series with the output prior to the capacitance. Figure 1 details starting points for the selection of this resistor. The points on the curve indicate the RS and CL combinations for the optimum bandwidth, stability, and settling time, but experimental fine tuning is recommended. Picking a point above or to the right of the curve yields an overdamped response, while points below or left of the curve indicate areas of underdamped performance. RS and CL form a low pass network at the output, thus limiting system bandwidth well below the amplifier bandwidth of 700MHz/540MHz (SOIC/SOT-23, AV = +2). By decreasing RS as CL increases (as illustrated by the curves), the maximum bandwidth is obtained without sacrificing stability. In spite of this, bandwidth still decreases as the load capacitance increases. For example, at AV = +2, RS = 20Ω, CL = 22pF, the SOIC bandwidth is 410MHz, but the bandwidth drops to 110MHz at AV = +2, RS = 5Ω, CL = 390pF. OPTIMUM FEEDBACK RESISTOR ACL RF (Ω) SOIC/SOT-23 BANDWIDTH (MHz) SOIC/SOT-23 -1 422/464 650/540 +1 383, (+RS = 226)/ 549, (+RS = 100) 600/500 +2 576/499 700/540 +5 348/422 480/400 +10 178/348 380/300 HFA1150 |
Numéro de pièce similaire - HFA1150 |
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Description similaire - HFA1150 |
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