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LP2951 データシート(PDF) 19 Page - Microchip Technology

部品番号 LP2951
部品情報  100 mA Low-Dropout Voltage Regulator
PDF  30 Pages
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メーカー  MICROCHIP [Microchip Technology]
ホームページ  http://www.microchip.com
Logo MICROCHIP - Microchip Technology

LP2951 データシート(HTML) 19 Page - Microchip Technology

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2017 - 2022 Microchip Technology Inc. and its subsidiaries
DS20005736B-page 19
LP2951
4.4
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 method is relatively
inefficient, as increasing the capacitor from 1µF to
220 µF only decreases the noise from 430 µV to
160 µVrms for a 100 kHz 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 the resulting frequency from
Equation 4-2:
EQUATION 4-2:
or about 0.01 µF. When doing this, the output capacitor
must be increased to 3.3 µF to maintain stability. These
changes reduce the output noise from 430 µV to
100 µVrms for a100 kHz 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 4-1:
ERROR Output Timing.
FIGURE 4-2:
Adjustable Regulator.
CBYPASS
1
2R1 200Hz
-----------------------------------
=
OUTPUT
VOLTAGE
INPUT
VOLTAGE
ERROR
NOT
VALID
NOT
VALID
5V
1.3V
4.75V
*
*
* SEE APPLICATIONS INFORMATION
*SEE APPLICATIONS
INFORMATION
NOTE: PINS 2 AND 6 ARE LEFT OPEN
LP2951
IN
OUT
GND
FB
ERROR
5
3
4
1
8
SD
V
V
ERROR
OUTPUT
SHUTDOWN
INPUT
IN
+V
100kΩ
OUT
V
1.2
30V
1
R
100
pF
3.3μF
2
R
1.23V
REF
V
7
OUT
V
REF
= V
x (1 +
)
1
R
2
R
OFF
ON
LP2951



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