MIC2937A/29371/29372

Micrel, Inc.

May 2006

9

MIC2937A/29371/29372

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),andverylowquiescentcurrents(100µAtypical).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.Awide operating temperature range with low

temperature coefficients is yet another reason to use these

versatile regulators in automotive designs.

Figure 2. MIC2937A-5.0 Fixed +5V Regulator

Figure 3. MIC29372 Adjustable Regulator

Typical Applications

Figure 5. MIC29372 5.0V or 3.3V Selectable Regulator with

Shutdown.

Figure 4. MIC29372 Wide Input Voltage Range Current Limiter

DEPENDING ON LOAD CURRENT.

SHUTDOWN PIN LOW= ENABLE OUTPUT. Q1 ON = 3.3V, Q1 OFF = 5.0V.

1

π

with a bypass capacitor across R

frequency gain from 4 to unity. Pick

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

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.

GND

+VIN

OUT

V

V

10µF

+

IN

VOUT = 5V

IN

OUT

GND ADJUST

SHUTDOWN

V

V

SHUTDOWN

INPUT

OUT

V

1.2V

26V

1

R .01

µF

10µF

2

R

1.23V

REF

V

VOUT = VREF x (1 +

)

1

R

2

R

OFF

ON

OUT

GND ADJUST

V

VIN

+VIN

VOUT ≈ VIN

SHUTDOWN

V

GND

OUT

+VIN

ADJUST

SHUTDOWN

INPUT

100pF

2N2222

1%

300kΩ

+5V to +7V

1%

180kΩ

+

10µF

470 k Ω

OFF

ON

5V

3.3V

220kΩ

1%

VCC OUT

Input Output

0

3.3V

1

5.0V