MIC2920A/29201/29202/29204
capacitor. This is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from
430µV to 160µV
RMS
for a 100kHz bandwidth at 5V output.
Noise can be reduced fourfold by a bypass capacitor across
R
1
, since it reduces the high frequency gain from 4 to unity.
Pick
1
C
BYPASS
≅
2
π
R
1
• 200 Hz
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
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.
Micrel
Automotive Applications
The MIC2920A 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.
Typical Applications
V IN
100kΩ
+VIN
VOUT
+
GND
*V OUT
≈5V
ERROR
OUTPUT
5 ERROR
+VIN
8
VIN
VOUT 1
VOUT
1.2 26V
V
OUT
= 5V
10µF
3
SHUTDOWN 3
SHUTDOWN
INPUT
OFF
ON
870
10µF
25
GND ADJUST
7
4
1.23V
R1
)
R2
V REF
R1 100
pF
VOUT = VREF x (1 +
R2
NOTE: PINS 2 AND 6 ARE LEFT OPEN
Figure 2. MIC2920A-5.0 Fixed +5V Regulator
Figure 3. MIC29202/29204 Adjustable Regulator. Pinout is for
MIC29204.
≥
5.3V
+VIN
8
8
+VIN
ERROR
OUTPUT
SHUTDOWN
INPUT
ON
+VIN
VCC OUT
VOUT
1
5 ERROR
3
OFF
*VOUT
≈V
IN
VOUT 1
SHUTDOWN
INPUT
3
HIGH = OFF
SHUT-
DOWN
100pF
GND
4
ADJUST
7
220kΩ
1%
2N2222
300kΩ
1%
MIC2951
LOW = ON
+
10µF
SD
GND
4
ADJUST
FB
7
HIGH = 5V OUT
470 kΩ
180kΩ
1%
LOW = 3.3V OUT
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40
m
V TO 400
m
V,
DEPENDING ON LOAD CURRENT.
PIN 3 LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.
Figure 4. MIC29204 Wide Input Voltage Range Current Limiter
Figure 5. MIC29202/29204 5.0V or 3.3V Selectable Regulator
with Shutdown. Pinout is for MIC29204.
January 1998
3-17
MICREL [ MICREL SEMICONDUCTOR ]
