MIC4690

Micrel

MIC4690

8

June 2001

Applications Information

Adjustable Regulators

Adjustable regulators require a 1.23V feedback signal. Rec-

ommended voltage-divider resistor values for common out-

put voltages are included in Figure 1b.

For other voltages, the resistor values can be determined

using the following formulas:

VV

R1

R2

1

R1 R2

V

V

1

V

1.23V

OUT

REF

OUT

REF

REF

=+









=−









=

SW

L1

VIN

FB

GND

SHDN

C2

220µF

10V

R1

3.01k

R2

1.27k

D1

2A

40V

5.0V/1A

MIC4690BM

C1

22µF

35V

+6.8V to +30V

SHUTDOWN

ENABLE

5Ð8

4

3

2

1

Power

SOP-8

18µH

Figure 1a. Adjustable Regulator Circuit

Bill of Material Matrix

V

OUT

V

IN

C

IN

D1

L1

C

OUT

I

OUT

5.0V

3.01k

976

Ω

6.8V-30V

22

µF, 35V

2A, 40V

18

µH

220

µF, 10V

see SOA

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D226X0035D2T

SS24

CDRH6D38-180ML

594D227X0010D2T

Micro Commercial

5.0V

3.01k

976

Ω

6.8V-14V

47

µF, 20V

2A, 20V

18

µH

100

µF, 6.3V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-180ML

595D107X06R3C2T

Micro Commercial

3.3V

3.01k

1.78k

4.9V-14V

47

µF, 20V

2A, 20V

15

µH

120

µF, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-150ML

595D127X0004C2T

Micro Commercial

2.5V

3.01k

2.94k

4.25V-14V 47

µF, 20V

2A, 20V

10

µH

120

µF, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-100ML

595D127X0004C2T

Micro Commercial

1.8V

3.01k

6.49k

4.0V-14V

47

µF, 20V

2A, 20V

10

µH

120

µF, 4.0V

1.0A

Vishay-Dale

Schotty

Sumida

Vishay-Dale

595D476X0020C2T

SS22

CDRH6D38-100ML

595D127X0004C2T

Micro Commercial

Note 1.

All resistors 1%

Figure 1b. Recommended Components for Common Ouput Voltages