LM7301IM National Semiconductor, LM7301IM Datasheet - Page 10

• Manufacturer Part Number: LM7301IM
• Description: IC, OP-AMP, 4MHZ, 1.25V/µs, SOIC-8
• Manufacturer: National Semiconductor

Specifications of LM7301IM

• Op Amp Type: Low Power
• No. Of Amplifiers: 1
• Bandwidth: 4MHz
• Slew Rate: 1.25V/µs
• Supply Voltage Range: 2.2V To 30V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Number Of Channels: 1
• Voltage Gain Db: 97.03 dB
• Common Mode Rejection Ratio (min): 70 dB
• Input Offset Voltage: 6 mV at 5 V
• Operating Supply Voltage: 3 V, 5 V, 9 V, 12 V, 15 V, 18 V, 24 V, 28 V
• Supply Current: 1.1 mA at 5 V
• Maximum Power Dissipation: 350 mW
• Maximum Operating Temperature: + 85 C
• Package / Case: SOIC-8 Narrow
• Maximum Dual Supply Voltage: +/- 16 V
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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STABILITY CONSIDERATIONS
Rail-to-rail output amplifiers like the LM7301 use the collector
of the drive transistor(s) at the output pin, as shown in
7. This allows the load to be driven as close as possible to-
wards either supply rail.
While this architecture maximizes the load voltage swing
range, it increases the dependence of loop gain and subse-
quently stability, on load impedance and DC load current,
compared to a non-rail-to-rail architecture. Thus, with this
type of output stage, it is even more crucial to ensure stability
by meticulous bench verification under all load conditions,
and to apply the necessary compensation or circuit modifica-
tions to overcome any instability, if necessary. Any such
bench verification should also include temperature, supply
voltage, input common mode and output bias point variations
as well as capacitive loading.
For example, one set of conditions for which stability of the
LM7301 amplifier may be compromised is when the DC out-
put load is larger than +/-0.5 mA, with input and output biased
to mid-rail. Under such conditions, it may be possible to ob-
serve open-loop gain response peaking at a high frequency
(e.g. 200 MHz), which is beyond the expected frequency
range of the LM7301 (4 MHz GBW). Without taking any pre-
cautions against gain peaking, it is possible to see increased
settling time or even oscillations, especially with low closed
loop gain and / or light AC loading. It is possible to reduce or
eliminate this gain peaking by using external compensation
components. One possible scheme that can be applied to re-
duce or eliminate this gain peaking is shown in
FIGURE 7. Simplified Output Stage Block Diagram
Figure
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Figure
8.
10
The non-dissipating snubber, consisting of R
AC load to reduce high frequency gain peaking with no DC
loading so that total power dissipation is not increased. The
increased AC load effectively reduces loop gain at higher fre-
quencies thereby reducing gain peaking due to the possible
causes stated above. For the particular set of R
ues shown in
25dB under worst case peaking conditions (I_source= 2mA
DC @ around 180MHz) thus confining loop gain below 0dB
and eliminating any possible instability. For best results, it
may be necessary to “tune” the values of R
ticular application to take into account other subtleties and
tolerances.
POWER DISSIPATION
Although the LM7301 has internal output current limiting,
shorting the output to ground when operating on a +30V pow-
er supply will cause the op amp to dissipate about 350 mW.
This is a worst-case example. In the 8-pin SOIC package, this
will cause a temperature rise of 58°C. In the 5-pin SOT23
package, the higher thermal resistance will cause a calculat-
ed rise of 113°C. This can raise the junction temperature to
above the absolute maximum temperature of 150°C.
Operating from split supplies greatly reduces the power dis-
sipated when the output is shorted. Operating on ±15V sup-
plies can only cause a temperature rise of 29°C in the 8-pin
SOIC and 57°C in the 5-pin SOT23 package, assuming the
short is to ground.
SPICE MACROMODEL
A SPICE macromodel for this and many other National Semi-
conductor operational amplifiers is available, at no charge,
from the NSC Customer Support Center at 800-272-9959 or
on the World Wide Web at http://www.national.com/models.
WIDE SUPPLY RANGE
The high power-supply rejection ratio (PSRR) and common-
mode rejection ratio (CMRR) provide precision performance
when operated on battery or other unregulated supplies. This
advantage is further enhanced by the very wide supply range
(2.2V–30V, guaranteed) offered by the LM7301. In situations
where highly variable or unregulated supplies are present, the
excellent PSRR and wide supply range of the LM7301 benefit
the system designer with continued precision performance,
even in such adverse supply conditions.
FIGURE 8. Non-dissipating Snubber Network to Reduce
Figure
8, loop gain peaking is reduced by about
Gain Peaking
c
c
and C
and C
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c
and C
c
c
in a par-
, acts as
c
val-