LP2950 Datasheet, PDF (16/26 Pages) National Semiconductor (TI) – Series of Adjustable Micropower Voltage Regulators

Application Hints (Continued)
REDUCING OUTPUT NOISE
In reference applications it may be advantageous to reduce
the AC noise present at the output. One method is to reduce
the regulator bandwidth by increasing the size of the output
capacitor. This is the only way noise can be reduced on the
3 lead LP2950 but is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from
430µV to 160µV rms for a 100kHz bandwidth at 5V output.
Noise can be reduced fourfold by a bypass capacitor across
R₁, since it reduces the high frequency gain from 4 to unity.
Pick
*See Application Hints
00854607
**Drive with TTL-high to shut down. Ground or leave open if shutdown
feature is not to be used.
Note: Pins 2 and 6 are left open.
or about 0.01µF. When doing this, the output capacitor must
be increased to 3.3µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV rms for a
100kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.
FIGURE 2. Adjustable Regulator
Typical Applications
1A Regulator with 1.2V Dropout
300mA Regulator with 0.75V Dropout
00854622
Wide Input Voltage Range Current Limiter
www.national.com
00854621
00854609
*Minimum input-output voltage ranges from 40mV to 400mV, depending on
load current. Current limit is typically 160mA.
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