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| 型号： | LM22674QMRX-ADJ/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 14/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.5A 8PSOP |
| 标准包装： | 2,500 |
| 系列： | SIMPLE SWITCHER® |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 1.285V |
| 输入电压： | 4.5 V ~ 42 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 500mA |
| 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 Width）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-PSOP |
SNVS590L – SEPTEMBER 2008 – REVISED APRIL 2013
Figure 17. Current Flow in a Buck Application
Thermal Considerations
The components with the highest power dissipation are the power diode and the power MOSFET internal to the
LM22674 regulator. The easiest method to determine the power dissipation within the LM22674 is to measure
the total conversion losses then subtract the power losses in the diode and inductor. The total conversion loss is
the difference between the input power and the output power. An approximation for the power diode loss is:
where
?
V D is the diode voltage drop.
(17)
An approximation for the inductor power is:
where
?
R L is the DC resistance of the inductor and the 1.1 factor is an approximation for the AC losses.
(18)
The regulator has an exposed thermal pad to aid power dissipation. Adding multiple vias under the device to the
ground plane will greatly reduce the regulator junction temperature. Selecting a diode with an exposed pad will
also aid the power dissipation of the diode. The most significant variables that affect the power dissipation of the
regulator are output current, input voltage and operating frequency. The power dissipated while operating near
the maximum output current and maximum input voltage can be appreciable. The junction-to-ambient thermal
resistance of the LM22674 will vary with the application. The most significant variables are the area of copper in
the PC board, the number of vias under the IC exposed pad and the amount of forced air cooling provided. A
large continuous ground plane on the top or bottom PCB layer will provide the most effective heat dissipation.
The integrity of the solder connection from the IC exposed pad to the PC board is critical. Excessive voids will
greatly diminish the thermal dissipation capacity. The junction-to-ambient thermal resistance of the LM22674 SO
PowerPAD package is specified in the Electrical Characteristics table. See application note AN-2020 ( SNVA419 )
for more information.
14
Product Folder Links: LM22674
Copyright ? 2008–2013, Texas Instruments Incorporated
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