lm6182 National Semiconductor Corporation, lm6182 Datasheet - Page 17

• Manufacturer Part Number: lm6182
• Description: Dual 100 Ma Output, 100 Mhz Current Feedback Amplifier
• Manufacturer: National Semiconductor Corporation

Typical Applications
The extent of the amplifier’s dependence on R
in Figure 5 for one particular closed-loop gain.
CAPACITIVE FEEDBACK
Current feedback amplifiers rely on feedback impedance for
proper compensation. Even in unity gain current feedback
amplifiers require a feedback resistor. LM6182 performance
is specified for a feedback resistance of 820 . Decreasing
the feedback impedance below 820 extends the amplifier’s
FIGURE 4. , 4B. Reducing R
FIGURE 5. −3 dB Bandwidth Is Determined By
Large Closed-Loop Gains, A
4A. R
4B. R
Selecting R
f
f
= 820
= 500
f
to Increase Bandwidth for
f
(Continued)
.
V
DS011926-27
= +25
f
is displayed
DS011926-25
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17
bandwidth leading to possible instability. Capacitive feed-
back should therefore not be used because the impedance
of a capacitor decreases with increasing frequency.
For voltage feedback amplifiers it is quite common to place a
small lead compensation capacitor in parallel with feedback
resistance, R
plifier’s peaking. One application of the lead compensation
capacitor is to counteract the effects of stray capacitance
from the inverting input to ground in circuit board layouts.
The LM6182 current feedback amplifier does not require this
lead compensation capacitor and has an even simpler, more
elegant solution.
To limit the bandwidth and peaking of the LM6182 current
feedback amplifier, do not use a capacitor across R
Figure 7 . This actually has the opposite effect and extends
the bandwidth of the amplifier leading to possible instability.
Instead, simply increase the value of the feedback resistor
as shown in Figure 3 .
Non-inverting applications can also reduce peaking and limit
bandwidth by adding an RC circuit as illustrated in Figure 8 .
FIGURE 6. Current Feedback Amplifiers are Unstable
FIGURE 7. Compensation Capacitors Are Not Used
with the LM6182, Instead Simply Increase R
f
. This compensation serves to reduce the am-
with Capacitive Feedback
Compensate
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DS011926-28
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f
to
f
as in