MIC2937A/29371/29372
with 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, Inc.
Automotive Applications
The MIC2937A is ideally suited for automotive applications
for a variety of reasons. It will operate over a wide range of
input voltages with very low dropout voltages (40mV at light
loads), and very low quiescent currents (100µA typical). These
features are necessary for use in battery powered systems,
such as automobiles. It is a “bulletproof” device with the abil-
ity to survive both reverse battery (negative transients up to
20V below ground), and load dump (positive transients up to
60V) conditions. A wide operating temperature range with low
temperature coefficients is yet another reason to use these
versatile regulators in automotive designs.
or about 0.01µF. When doing this, the output capacitor must
be increased to 10µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV
RMS
for a 100
kHz bandwidth at 5V output. With the bypass capacitor added,
noise no longer scales with output voltage so that improve-
ments are more dramatic at higher output voltages.
Typical Applications
VIN
+VIN
VOUT
+
GND
VOUT = 5V
SHUTDOWN
INPUT
OFF
VIN
VOUT
VOUT
1.2V
26V
SHUTDOWN
GND ADJUST
1.23V
10µF
ON
R1 .01
µF
10µF
V REF
R1
VOUT = VREF x (1 +
)
R2
R2
Figure 2. MIC2937A-5.0 Fixed +5V Regulator
Figure 3. MIC29372 Adjustable Regulator
+5V to +7V
+VIN
+V IN
V CC OUT
VOUT
SHUTDOWN
OFF
ON
VIN
VOUT
VOUT ≈ VIN
SHUTDOWN
INPUT
GND
ADJUST
100pF
300k Ω
1%
+
10µF
GND
ADJUST
5V
3.3V
Input
0
1
Output
3.3V
5.0V
470 k Ω
220k Ω
1%
2N2222
180k Ω
1%
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40
m
V TO 400
m
V,
DEPENDING ON LOAD CURRENT.
SHUTDOWN PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.
Figure 4. MIC29372 Wide Input Voltage Range Current Limiter
Figure 5. MIC29372 5.0V or 3.3V Selectable Regulator with
Shutdown.
May 2006
9
MIC2937A/29371/29372
MICREL [ MICREL SEMICONDUCTOR ]
