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参数资料
| 型号： | LM2830ZQMFE |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 3750 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封装： | SOT-23, 5 PIN |
| 文件页数： | 6/24页 |
| 文件大小： | 508K |
| 代理商： | LM2830ZQMFE |
Thermal impedance from the silicon junction to the ambient
air is defined as:
The PCB size, weight of copper used to route traces and
ground plane, and number of layers within the PCB can great-
ly effect RθJA. The type and number of thermal vias can also
make a large difference in the thermal impedance. Thermal
vias are necessary in most applications. They conduct heat
from the surface of the PCB to the ground plane. Four to six
thermal vias should be placed under the exposed pad to the
ground plane if the LLP package is used.
Thermal impedance also depends on the thermal properties
of the application operating conditions (Vin, Vo, Io etc), and
the surrounding circuitry.
Silicon Junction Temperature Determination Method 1:
To accurately measure the silicon temperature for a given
application, two methods can be used. The first method re-
quires the user to know the thermal impedance of the silicon
junction to top case temperature.
Some clarification needs to be made before we go any further.
RθJC is the thermal impedance from all six sides of an IC
package to silicon junction.
RΦJC is the thermal impedance from top case to the silicon
junction.
In this data sheet we will use RΦJC so that it allows the user
to measure top case temperature with a small thermocouple
attached to the top case.
RΦJC is approximately 30°C/Watt for the 6-pin LLP package
with the exposed pad. Knowing the internal dissipation from
the efficiency calculation given previously, and the case tem-
perature, which can be empirically measured on the bench
we have:
Therefore:
T
j = (R
ΦJC x PLOSS) + TC
From the previous example:
T
j = (R
ΦJC x PINTERNAL) + TC
T
j = 30°C/W x 0.189W + TC
The second method can give a very accurate silicon junction
temperature.
The first step is to determine RθJA of the application. The
LM2830 has over-temperature protection circuitry. When the
silicon temperature reaches 165°C, the device stops switch-
ing. The protection circuitry has a hysteresis of about 15°C.
Once the silicon temperature has decreased to approximately
150°C, the device will start to switch again. Knowing this, the
RθJA for any application can be characterized during the early
stages of the design one may calculate the RθJA by placing
the PCB circuit into a thermal chamber. Raise the ambient
temperature in the given working application until the circuit
enters thermal shutdown. If the SW-pin is monitored, it will be
obvious when the internal PFET stops switching, indicating a
junction temperature of 165°C. Knowing the internal power
dissipation from the above methods, the junction tempera-
ture, and the ambient temperature RθJA can be determined.
Once this is determined, the maximum ambient temperature
allowed for a desired junction temperature can be found.
An example of calculating RθJA for an application using the
National Semiconductor LM2830 LLP demonstration board is
shown below.
The four layer PCB is constructed using FR4 with oz copper
traces. The copper ground plane is on the bottom layer. The
ground plane is accessed by two vias. The board measures
3.0cm x 3.0cm. It was placed in an oven with no forced airflow.
The ambient temperature was raised to 144°C, and at that
temperature, the device went into thermal shutdown.
From the previous example:
P
INTERNAL = 189mW
If the junction temperature was to be kept below 125°C, then
the ambient temperature could not go above 109°C
T
j - (R
θJA x PLOSS) = TA
125°C - (111°C/W x 189mW) = 104°C
LLP Package
20197468
FIGURE 4. Internal LLP Connection
For certain high power applications, the PCB land may be
modified to a "dog bone" shape (see Figure 6). By increasing
the size of ground plane, and adding thermal vias, the RθJA
for the application can be reduced.
www.national.com
14
LM2830
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2830ZQMFE/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2830ZQMFX/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2830ZSD | 功能描述:直流/直流开关调节器 RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| LM2830ZSD/NOPB | 功能描述:直流/直流开关调节器 RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
| LM2830ZSDX | 功能描述:直流/直流开关调节器 RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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