MIC4682

Micrel

October 2003

12

M0334-102203

SW

L1

68

µH

IN

FB

GND

SHDN

R1

R2

D1

MIC4682BM

GND

+4V to +34V

Power

SOP-8

267

3

1

8

5

4

Figure 4. Critical Traces for Layout

SW

L1

68

µH

IN

GND

GND

GND

SHDN

FB

ISET

D1

B340A

J3

J4

GND

U1 MIC4682BM

JP1 1-2=OFF

JP1 2-3-ON

C3

0.1

µF

50V

J1

4V to 34V

2

6

7

1

2

1

12

8

5

4

3

2

1

3

J2

GND

JP1

ON

OFF

C5

220

µF

10V

C6

Option

C4

Option

R5

6.49k

JP2a

1.8V

R4

2.94k

R1

3.01k

R2

976

C2

10

µF

50V

C1

10

µF

50V

C7

0.1

µF

50V

JP2b

2.5V

JP2d

5.0V

2

1

4

3

R3

1.78k

JP2c

3.3V

6

5

8

7

R8

option

JP3c

2.0A

R7

16.2k

R6

25k

R9

10M

JP3b

1.0A

JP3a

0.6A

2

1

4

3

6

5

Figure 5a. Evaluation Board Schematic Diagram

T

entry point of pins 6 or 7.

T

for the specific design.

Calculating the maximum junction temperature given a

maximum ambient temperature of 65

°C:

T

T

This value is within the allowable maximum operating junc-

tion temperature of 125

°C as listed in “Operating Ratings.”

Typical thermal shutdown is 160

°C and is listed in “Electrical

Characteristics.”

Layout Considerations

Layout is very important when designing any switching regu-

lator. Rapidly changing currents through the printed circuit

board traces and stray inductance can generate voltage

transients which can cause problems.

To minimize stray inductance and ground loops, keep trace

lengths, indicated by the heavy lines in Figure 4, as short as

possible. For example, D1 should be close to pin 7 and pin 8.

C

Information: Thermal Considerations” for ground plane lay-

out.

The feedback pin should be kept as far way from the switching

elements (usually L1 and D1) as possible.

A circuit with sample layouts are provided. See Figures 5a

though 5e. Gerber files are available upon request.