LM149 National Semiconductor, LM149 Datasheet - Page 4

• Manufacturer Part Number: LM149
• Description: Quad 741 Op Amps LM149 Wide Band Decompensated (AV MIN = 5)
• Manufacturer: National Semiconductor

www.national.com
Application Hints
Like the LM741, these amplifiers can easily drive a 100 pF
capacitive load throughout the entire dynamic output voltage
and current range. However, if very large capacitive loads
must be driven by a non-inverting unity gain amplifier, a re-
sistor should be placed between the output (and feedback
connection) and the capacitance to reduce the phase shift
resulting from the capacitive loading.
The output current of each amplifier in the package is limited.
Short circuits from an output to either ground or the power
supplies will not destroy the unit. However, if multiple output
shorts occur simultaneously, the time duration should be
short to prevent the unit from being destroyed as a result of
excessive power dissipation in the IC chip.
As with most amplifiers, care should be taken lead dress,
component placement and supply decoupling in order to en-
Typical Performance Characteristics
Supply Current
Positive Current Limit
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(Continued)
Input Bias Current
Negative Current Limit
4
sure stability. For example, resistors from the output to an in-
put should be placed with the body close to the input to mini-
mize “pickup” and maximize the frequency of the feedback
pole which capacitance from the input to ground creates.
A feedback pole is created when the feedback around any
amplifier is resistive. The parallel resistance and capacitance
from the input of the device (usually the inverting input) to AC
ground set the frequency of the pole. In many instances the
frequency of this pole is much greater than the expected 3
dB frequency of the closed loop gain and consequently there
is negligible effect on stability margin. However, if the feed-
back pole is less than approximately six times the expected
3 dB frequency a lead capacitor should be placed from the
output to the input of the op amp. The value of the added ca-
pacitor should be such that the RC time constant of this ca-
pacitor and the resistance it parallels is greater than or equal
to the original feedback pole time constant.
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Voltage Swing
Output Impedance
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