LM6181IM-8 National Semiconductor, LM6181IM-8 Datasheet - Page 21

• Manufacturer Part Number: LM6181IM-8
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LM6181IM-8

• No. Of Amplifiers: 1
• Bandwidth: 100MHz
• No. Of Pins: 8
• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Package / Case: 8-NSOIC
• Number Of Channels: 1
• Common Mode Rejection Ratio (min): 50 dB
• Input Offset Voltage: 3 mV at +/- 5 V
• Operating Supply Voltage: 9 V, 12 V, 15 V, 18 V, 24 V, 28 V
• Supply Current: 8.5 mA at +/- 5 V
• Maximum Operating Temperature: + 85 C
• Maximum Dual Supply Voltage: +/- 16 V
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Typical Applications
CURRENT FEEDBACK TOPOLOGY
For a conventional voltage feedback amplifier the resulting
small-signal bandwidth is inversely proportional to the de-
sired gain to a first order approximation based on the gain-
bandwidth concept. In contrast, the current feedback ampli-
fier topology, such as the LM6181, transcends this limitation
to offer a signal bandwidth that is relatively independent of
the closed-loop gain. Figure 1a and Figure 1b illustrate that
for closed loop gains of −1 and −5 the resulting pulse fidelity
suggests quite similar bandwidths for both configurations.
The closed-loop bandwidth of the LM6181 depends on the
feedback resistance, R
varied to adjust for the desired closed-loop gain as in Figure
2.
FIGURE 1. 1a, 1b: Variation of Closed Loop Gain
from −1 to −5 Yields Similar Responses
f
. Therefore, R
1a
1b
S
and not R
f
, must be
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21
POWER SUPPLY BYPASSING AND LAYOUT
CONSIDERATIONS
A fundamental requirement for high-speed amplifier design
is adequate bypassing of the power supply. It is critical to
maintain a wideband low-impedance to ground at the ampli-
fiers supply pins to insure the fidelity of high speed amplifier
transient signals. 10 µF tantalum and 0.1 µF ceramic bypass
capacitors are recommended for each supply pin. The by-
pass capacitors should be placed as close to the amplifier
pins as possible (0.5" or less).
FEEDBACK RESISTOR SELECTION: R
Selecting the feedback resistor, R
compensating the LM6181. For general applications the
LM6181 will maintain specified performance with an 820Ω
feedback resistor. Although this value will provide good re-
sults for most applications, it may be advantageous to adjust
this value slightly. Consider, for instance, the effect on pulse
responses with two different configurations where both the
closed-loop gains are 2 and the feedback resistors are 820Ω
and 1640Ω, respectively. Figure 3a and Figure 3b illustrate
the effect of increasing R
closed-loop gain — the amplifier bandwidth decreases. Ac-
cordingly, larger feedback resistors can be used to slow
down the LM6181 (see −3 dB bandwidth vs R
and reduce overshoot in the time domain response. Con-
versely, smaller feedback resistance values than 820Ω can
be used to compensate for the reduction of bandwidth at
high closed loop gains, due to 2nd order effects. For ex-
ample Figure 4 illustrates reducing R
the desired small signal response in an amplifier configured
for a closed loop gain of 25.
the Desired Closed Loop Gain, A
FIGURE 2. R
S
Is Adjusted to Obtain
f
while maintaining the same
f
, is a dominant factor in
f
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to 500Ω to establish
f
f
typical curves)
VCL
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