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| 型号： | MIC4680YM TR |
| 厂商： | Micrel Inc |
| 文件页数： | 12/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1.3A 8SOIC |
| 标准包装： | 1 |
| 系列： | SuperSwitcher™ |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 1.25V |
| 输入电压： | 4 V ~ 34 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 200kHz |
| 电流 - 输出： | 1.3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-SOIC |
| 产品目录页面： | 1093 (CN2011-ZH PDF) |
| 其它名称： | 576-1222-6 |
Micrel, Inc.
MIC4680
P D =
P D =
P OUT
η
5W
0.79
? P OUT
? 5W
Layout Considerations
Layout is very important when designing any switching
regulator. Rapidly changing switching currents through
the printed circuit board traces and stray inductance can
generate voltage transients which can cause problems.
P D = 1.33W
Calculate the worst-case junction temperature:
T J = P D(IC) θ JC + (T C – T A ) + T A(max)
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
IN
SW
where:
T J = MIC4680 junction temperature
P D(IC) = MIC4680 power dissipation
θ JC = junction-to-case thermal resistance.
The θ JC for the MIC4680’s power-SOIC-8
is approximately 20°C/W. (Also see Figure
1.)
T C = “pin” temperature measurement taken at
the entry point of pins 6 or 7 into the
FB, and keep C IN close to pin 2 and pins 5 though 8. See
“Applications Information: Thermal Considerations” for
ground plane layout.
The feedback pin should be kept as far way from the
switching elements (usually L1 and D1) as possible.
A circuit with sample layouts is provided. See Figure 6a
through 6e.
MIC4680BM
3
plastic package at the ambient
temperature (T A ) at which T C is measured.
T A = ambient temperature at which T C is
measured.
T A(max) = maximum ambient operating temp. for
the specific design.
SHDN
GND
5 6 7 8
FB
1N4148
2.2nF
D1
Calculating the maximum junction temperature given a
maximum ambient temperature of 65°C:
TJ = 1.064 × 20°C/W + (45°C – 25°C) + 65°C
TJ = 106.3°C
Figure 4. Increasing Maximum Output Current
at High Input Voltages
This value is less than the allowable maximum operating
junction temperature of 125°C as listed in “Operating
Ratings.” Typical thermal shutdown is 160°C and is
listed in “Electrical Characteristics.”
V IN
+4V to +34V
C IN
2
1
MIC4680BM
IN SW
SHDN FB
3
4
L1
68μH
C OUT
V OUT
R1
Increasing the Maximum Output Current
The maximum output current at high input voltages can
Power
SOIC-8
GND
5 6 7 8
D1
R2
be increased for a given board layout. The additional
three components shown in Figure 4 will reduce the
overall loss in the MIC4680 by about 20% at high V IN
and high I OUT .
Even higher output current can be achieved by using the
MIC4680 to switch an external FET. See Figure 9 for a
5A supply with current limiting.
J1
Figure 5. Critical Traces for Layout
J2
GND
V IN
4V to +34V
C1
15μF
35V
J3
GND
OFF
ON
C2
0.1μF
50V
S1
NKK G12AP
2
1
U1 MIC4680BM
IN SW
SHDN FB
GND
SOIC-8 5–8
3
4
L1
68μH
D1 R6
B260A optional
or
SS26
1
R1
3.01k
R2
6.49k
JP1a
3
C3*
optional
R3
2.94k
5
JP1b
R4
1.78k
JP1c
7
R5
JP1d
C4
220μF
10V
V OUT
1A
C5
0.1μF
50V
* C3 can be used to provide additional stability
2
1.8V
4
2.5V
6
3.3V
8
5.0V
J4
GND
and improved transient response.
Figure 6a. Evaluation Board Schematic Diagram
March 2008
12
M9999-032808
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