MIC2937A/29371/29372

Micrel

MIC2937A/29371/29372

26

October 1999

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 (100

µA 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.

OUT

GND

+VIN

*V

≈5V

OUT

V

V

10µF

+

IN

V

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.

SHUTDOWN

V

GND

OUT

+VIN

ADJUST

SHUTDOWN

INPUT

100pF

2N2222

1%

300k

Ω

+5V to +7V

1%

180k

Ω

+

10µF

470 k

Ω

OFF

ON

5V

3.3V

220k

Ω

1%

VCC OUT

Input

Output

0

3.3V

1

5.0V

OUT

GND

ADJUST

V

VIN

+VIN

VOUT ≈ VIN

≅

1

π

regulators with a bypass capacitor across R

1

, since it reduces

the high frequency gain from 4 to unity. Pick

or about 0.01

µF. When doing this, the output capacitor must

be increased to 10

µF to maintain stability. These changes

reduce the output noise from 430

µV to 100µV

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.

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