MIC4682 Datasheet, PDF (12/15 Pages) Micrel Semiconductor – PRECISION CURRENT LIMIT SO-8 SUPERSWITCHER BUCK REGULATOR

MIC4682
T_C = “pin” temperature measurement taken at the
entry point of pins 6 or 7.
T_A = ambient temperature
T_A(max) = maximum ambient operating temperature
for the specific design.
Calculating the maximum junction temperature given a
maximum ambient temperature of 65°C:
T_J = 0.936 × 20°C/W + (45°C – 25°C) + 65°C
T_J = 103.7°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.”
Micrel
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_IN should be close to pin 5 and pin 6. See “Applications
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.
V_IN
+4V to +34V
C_IN
Power
SOP-8
MIC4682BM
5 _IN
SW ⁸
4 _SHDN
FB ¹
GND I_SET
267 3
L1
68µH
D1
V_OUT
C_OUT R1
R2
GND
Figure 4. Critical Traces for Layout
J1
V_IN
4V to 34V
C1
10µF
50V
J2
GND
C2
10µF
50V
C3
0.1µF
50V
1
OFF
ON
JP1 1-2=OFF
JP1 2-3-ON
2
JP1
3
R9
10M
U1 MIC4682BM
5 _IN
SW ⁸
1
4 _SHDN
3 _ISET
GND ⁷
2
FB ¹
R8
R7
R6
option 16.2k 25k
2 _JP3c 4 _JP3b 6 _JP3a
2.0A 1.0A 0.6A
1
3
5
GND GND
2
6
L1
68µH
1
2
D1
B340A _R1
3.01k
C4
Option
R5
R4
6.49k 2.94k
R3
1.78k
2 _JP2a 4 _JP2b 6 _JP2c 8
1.8V 2.5V 3.3V
1
3
5
7
R2
976
JP2d
5.0V
C5
220µF
10V
C6
Option
J3
V_OUT
C7
0.1µF
50V
J4
GND
Figure 5a. Evaluation Board Schematic Diagram
October 2003
12
M0334-102203