HFA1150IH96 データシートの表示（PDF） - Intersil
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HFA1150IH96 Datasheet PDF : 13 Pages
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HFA1150
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.
OPTIMUM FEEDBACK RESISTOR
RF (Ω)
BANDWIDTH (MHz)
ACL
SOIC/SOT-23
SOIC/SOT-23
-1
422/464
650/540
+1
383, (+RS = 226)/
600/500
549, (+RS = 100)
+2
576/499
700/540
+5
348/422
480/400
+10
178/348
380/300
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.
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