参数资料
| 型号： | MIC33153YHJ TR |
| 厂商： | Micrel Inc |
| 文件页数： | 13/17页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 1.2A 14MLF |
| 标准包装： | 1 |
| 系列： | HyperLight Load® |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.62 V ~ 3.6 V |
| 输入电压： | 2.7 V ~ 5.5 V |
| PWM 型： | 混合物 |
| 频率 - 开关： | 4MHz |
| 电流 - 输出： | 1.2A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-VFDFN 裸露焊盘，14-MLF? |
| 包装： | 标准包装 |
| 供应商设备封装： | 14-MLF?（3x3.5） |
| 其它名称： | 576-3904-6 |
P DISS = P OUT × ( ? 1)
Micrel Inc.
Power Dissipation Considerations
As with all power devices, the ultimate current rating of
the output is limited by the thermal properties of the
package and the PCB it is mounted on. There is a
simple, Ohm’s law type of relationship between thermal
resistance, power dissipation and temperature which is
analogous to an electrical circuit:
From this simple circuit, one can calculate V X if one
knows I SOURCE , V Z and the resistor values, R XY and R YZ
using the equation:
V X = I SOURCE × ( R XY + R YZ ) + V Z
Thermal circuits can be considered using these same
rules and can be drawn similarly replacing current
sources with power dissipation (in Watts), resistance
with thermal resistance (in o C/W) and voltage sources
with temperature (in o C):
MIC33153
As can be seen in the diagram, total thermal resistance
R θ JA = R θ JC + R θ CA . Hence this can also be written:
T J = P DISS × ( R θ JA ) + T AMB
Since effectively all of the power loss in the converter is
dissipated within the MIC33153 package, P DISS can be
calculated thus:
1
η
Where:
η = Efficiency taken from efficiency curves
R θ JC and R θ JA are found in the operating ratings section
of the datasheet.
Example:
A MIC33153 is intended to drive a 1A load at 1.8V and is
placed on a printed circuit board which has a ground
plane area of at least 25mm square. The voltage source
is a Li-ion battery with a lower operating threshold of 3V
and the ambient temperature of the assembly can be up
to 50 o C.
Summary of variables:
I OUT = 1A
V OUT = 1.8V
V IN = 3V to 4.2V
T AMB = 50 o C
R θ JA = 55 o C/W from Datasheet
η @ 1A = 80% (worst case with V IN =4.2V from the
Typical Characteristics Efficiency vs. Load graphs)
P DISS = 1.8 ? 1 × (
1
0.80
? 1) = 0.45W
Now replacing the variables in the equation for V X , one
can find the junction temperature (T J ) from power
dissipation, ambient temperature and the known thermal
resistance of the PCB (R θ CA ) and the package (R θ JC ):
T J = P DISS × ( R θ JC + R θ CA ) + T AMB
The worst case switch and inductor resistance will
increase at higher temperatures, so a margin of 20% can
be added to account for this:
P DISS = 0.45 x 1.2 = .54W
Therefore:
T J = 0.54W x (55 o C/W) + 50 o C
T J = 79.7 o C
This is well below the maximum 125 o C.
September 2010
13
M9999-092910-A
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