MIC2950/2951
Noise can be reduced fourfold by a bypass capacitor across
R
1
, since it reduces the high frequency gain from 4 to unity.
Pick:
C
BYPASS
≅
1
2
π
R
1
• 200 Hz
Micrel
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
µV
rms for a 100
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.
4.75V
OUTPUT
VOLTAGE
100kΩ
+VIN
8
VIN
VOUT 1
ERROR
NOT
*
VALID
NOT
*
VALID
ERROR
OUTPUT
5 ERROR
MIC2951
VOUT = V REF
R
x (1 + 1 )
R2
VOUT
1.2 30V
INPUT
VOLTAGE
1.3V
5V
ON
SHUTDOWN 3
SD
INPUT
OFF
3.3µF
GND
4
FB
7
R1 100
pF
1.23V
R2
3
V REF
* SEE APPLICATIONS INFORMATION
NOTE: PINS 2 AND 6 ARE LEFT OPEN
*SEE APPLICATIONS
INFORMATION
Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
870 23
Typical Applications
+V IN
*SLEEP
INPUT
47kΩ
8
+V IN
ERROR
OUTPUT
5
ERROR
V OUT 1
C-MOS
GATE
+VIN
8
+VIN
ERROR
OUTPUT
+V OUT
470 kΩ
5 ERROR
3
OFF
*VOUT
≈V
IN
VOUT 1
870 25
MIC2951
SHUTDOWN
INPUT
SD
GND
4
FB
7
MIC2951
3
SHUTDOWN
SD
INPUT
OFF
FB
GND
ON
7
4
200kΩ
1%
+
2N3906
100kΩ
100pF
3.3µF
ON
1%
100kΩ
*HIGH INPUT LOWERS V
OUT
TO 2.5V
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40
m
V TO 400
m
V,
DEPENDING ON LOAD CURRENT.
5V Regulator with 2.5V Sleep Function
Wide Input Voltage Range Current Limiter
February 1999
3-59
MICREL [ MICREL SEMICONDUCTOR ]
