MIC4681_05 MICREL [Micrel Semiconductor], MIC4681_05 Datasheet - Page 13

• Manufacturer Part Number: MIC4681_05
• Description: 2A-Peak SuperSwitcher SOP-8 Buck Regulator
• Manufacturer: MICREL [Micrel Semiconductor]

for the specific design.
Calculating the maximum junction temperature given a
maximum ambient temperature of 65 C:
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 5, as short as
possible. For example, keep D1 close to pin 3 and pins 5
through 8, keep L1 away from sensitive node FB, and keep
April 2005
MIC4681
T
T
T
T
A
A(max)
J
J
= 1.064
= 106.3 C
= ambient temperature
4V to +30V
= maximum ambient operating temperature
GND
V
J1
J3
IN
22 F
35V
C1
* C3 can be used to provide additional stability
20 C/W + (45 C – 25 C) + 65 C
and improved transient response.
OFF
ON
JP1
0.1 F
50V
C2
+4V to +30V
Power
SOP-8
Figure 6a. Evaluation Board Schematic Diagram
V
IN
2
1
SOP-8
IN
SHDN
C
U1 MIC4681BM
IN
Figure 5. Critical Traces for Layout
GND
2
1
5–8
IN
SHDN
MIC4681BM
SW
FB
5 6 7 8
GND
3
4
SW
D1
B340A
or
SS36
FB
13
3
4
68 H
L1
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 6a
though 6e. Gerber files are available upon request.
R6
optional
IN
D1
68 H
close to pin 2 and pins 5 though 8. See “Applications
L1
1
2
R1
3.01k
R2
6.49k
JP2a
1.8V
3
4
C
OUT
R3
2.94k
JP2b
2.5V
C3* 1800pF / 50V
optional
R1
R2
5
6
GND
V
OUT
R4
1.78k
JP2c
3.3V
7
8
R5
976
JP2d
5.0V
C4
220 F
10V
V
GND
C5
0.1 F
50V
1A
J2
OUT
J4
MIC4681
Micrel