MIC2937A/29371/29372
regulators 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
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 ability 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
improvements are more dramatic at higher output voltages.
Typical Applications
V IN
+VIN
VOUT
+
GND
ON
*V OUT
≈5V
VIN
V
OUT
= 5V
10µF
VOUT
SHUTDOWN
INPUT
OFF
VOUT
1.2V
26V
SHUTDOWN
GND ADJUST
1.23V
R1 .01
µF
10µF
R1
VOUT = VREF x (1 +
)
R2
V REF
R2
Figure 2. MIC2937A-5.0 Fixed +5V Regulator
Figure 3. MIC29372 Adjustable Regulator
+5V to +7V
+VIN
VIN
VOUT
VOUT
≈
VIN
+VIN
SHUTDOWN
INPUT
OFF
ON
VCC OUT
VOUT
SHUTDOWN
+
100pF
GND
ADJUST
300kΩ
1%
10µF
GND
ADJUST
470 kΩ
220kΩ
1%
2N2222
Input
0
1
Output
3.3V
5.0V
5V
3.3V
180kΩ
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.
MIC2937A/29371/29372
26
October 1999
MICREL [ MICREL SEMICONDUCTOR ]
