lm6162 National Semiconductor Corporation, lm6162 Datasheet - Page 8

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lm6162

Manufacturer Part Number
lm6162
Description
High Speed Operational Amplifier
Manufacturer
National Semiconductor Corporation
Datasheet
www.national.com
Simplified Schematic
Application Tips
The LM6162 has been decompensated for a wider
gain-bandwidth product than the LM6361. However, the
LM6162 still offers stability at gains of 2 (and −1) or greater
over the specified ranges of temperature, power supply volt-
age, and load. Since this decompensation involved reducing
the emitter-degeneration resistors in the op amp’s input
stage, the DC precision has been increased in the form of
lower offset voltage and higher open-loop gain.
Other op amps in this family include the LM6361, LM6364,
and LM6365. If unity-gain stability is required, the LM6361
should be used. The LM6364 has been decompensated for
operation at gains of 5 or more, with corresponding greater
gain-bandwidth product (125 MHz, typical) and DC preci-
sion.
gain-bandwidth product of 725 MHz, typical, and is stable for
gains of 25 or more. All parts in this family, regardless of
compensation, have the same high slew rate of 300 V/µs
(typ).
The LM6162 is unusually tolerant of capacitive loads. Most
op amps tend to oscillate when their load capacitance is
greater than about 200 pF (in low-gain circuits). However,
load capacitance on the LM6162 effectively increases its
compensation capacitance, thus slowing the op amp’s re-
sponse and reducing its bandwidth. The compensation is not
ideal, though, and ringing may occur in low-gain circuits with
large capacitive loads.
The
fully-uncompensated
LM6365
offers
8
Power supply bypassing is not as critical for LM6162 as it is
for other op amps in its speed class. However, bypassing will
improve the stability and transient response of the LM6162,
and is recommended for every design. 0.01 µF to 0.1 µF ce-
ramic capacitors should be used (from each supply “rail” to
ground); if the device is far away from its power supply
source, an additional 2.2 µF to 10 µF of tantalum may be re-
quired for extra noise reduction.
Keep all leads short to reduce stray capacitance and lead in-
ductance, and make sure ground paths are low-impedance,
especially where heavier currents will be flowing. Stray ca-
pacitance in the circuit layout can cause signal coupling from
one pin, input or lead to another, and can cause circuit gain
to unintentionally vary with frequency.
Breadboarded circuits will work best if they are built using
generic PC boards with a good ground plane. If the op amps
are used with sockets, as opposed to being soldered into the
circuit, the additional input capacitance may degrade circuit
frequency response. At low gains (+2 or −1), a feedback ca-
pacitor C
the phase lag caused by capacitance at the inverting input.
Typically, values from 2 pF to 5 pF work well; however, best
results can be obtained by observing the amplifier pulse re-
sponse and optimizing C
f
from output to inverting input will compensate for
f
for the particular layout.
DS011061-1

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