SPX2954 データシートの表示（PDF） - Unspecified

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SPX2954

250mA Low Dropout Voltage Regulator

Unspecified 

Reducing Output Noise

It may be an advantage to reduce the AC noise present at

the output. One way is to reduce the regulator bandwidth by

increasing the size of the output capacitor. This is the only

way that noise can be reduced on the 3 lead SPX2954 but is

relatively inefficient, as increasing the capacitor from 1µF to

220µF only decreases the noise from 430µV to 160µVRMS

for a 100kHz bandwidth at 5V output. Noise can be reduced

fourfold by using a bypass capacitor across R1, since it

reduces the high frequency gain from 4 to unity. Pick

CBYPASS ≈ (1 / 2πR1 x 200Hz)

or choose 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 100µVRMS 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.

+V IN

470KΩ

8

5 _____

+VIN

ERROR

470KΩ

SPX2954

1

V OUT

3

SD

R1

RESET

GND

FB

4

7

V OUT

+

1μF

R2

SPX2954

+VIN

ERROR

OUTPUT

SHUTDOWN

INPUT

8

5 ______

+VIN

ERROR

1

VOUT

SPX2954

3

SD

GND

FB

4

7

*VOUT =VIN

*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV to 400mV.

DEPENDING ON LOAD CURRENT.

Figure 3. Wide Input Voltage Range, Current Limiter

Figure 2. Latch Off when Error Flag Occurs

REV1A

10/15

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