SPX2954 Datasheet, PDF (10/15 Pages) Sipex Corporation – 250 mA Low Drop Out Voltage Regulator

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
C_BYPASS ≈ (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 _____
+V_IN
ERROR
470KΩ
SPX2954
1
V _OUT
3
SD
R₁
RESET
GND
FB
4
7
V _OUT
+
1μF
R₂
SPX2954
+V_IN
ERROR
OUTPUT
SHUTDOWN
INPUT
8
5 ^______
+V_IN
ERROR
1
V_OUT
SPX2954
3
SD
GND
FB
4
7
*V_OUT =V_IN
*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