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| 型号： | LM22674QMRX-5.0/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 13/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 0.5A 8PSOP |
| 标准包装： | 2,500 |
| 系列： | SIMPLE SWITCHER® |
| 类型： | 降压（降压） |
| 输出类型： | 固定 |
| 输出数： | 1 |
| 输出电压： | 5V |
| 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
Vout
R FBT
FB
R FBB
Figure 16. Resistive Feedback Divider
A maximum value of 10 k ? is recommended for the sum of R FBB and R FBT to maintain good output voltage
accuracy for the -ADJ option. A maximum of 2 k ? is recommended for the -5.0 option. For the -5.0 option, the
total internal divider resistance is typically 9.93 k ? .
In all cases the output voltage divider should be placed as close as possible to the FB pin of the LM22674; since
this is a high impedance input and is susceptible to noise pick-up.
POWER DIODE
A Schottky type power diode is required for all LM22674 applications. Ultra-fast diodes are not recommended
and may result in damage to the IC due to reverse recovery current transients. The near ideal reverse recovery
characteristics and low forward voltage drop of Schottky diodes are particularly important for high input voltage
and low output voltage applications common to the LM22674. The reverse breakdown rating of the diode should
be selected for the maximum V IN , plus some safety margin. A good rule of thumb is to select a diode with a
reverse voltage rating of 1.3 times the maximum input voltage.
Select a diode with an average current rating at least equal to the maximum load current that will be seen in the
application.
Circuit Board Layout
Board layout is critical for the proper operation of switching power supplies. First, the ground plane area must be
sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects
of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of
input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The
magnitude of this noise tends to increase as the output current increases. This noise may turn into
electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, care must be
taken in layout to minimize the effect of this switching noise.
The most important layout rule is to keep the AC current loops as small as possible. Figure 17 shows the current
flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the FET
switch on-state. The middle schematic shows the current flow during the FET switch off-state.
The bottom schematic shows the currents referred to as AC currents. These AC currents are the most critical
since they are changing in a very short time period. The dotted lines of the bottom schematic are the traces to
keep as short and wide as possible. This will also yield a small loop area reducing the loop inductance. To avoid
functional problems due to layout, review the PCB layout example. Best results are achieved if the placement of
the LM22674, the bypass capacitor, the Schottky diode, R FFB , R FFT , and the inductor are placed as shown in the
example. Note that, in the layout shown, R1 = R FBB and R2 = R FBT . It is also recommended to use 2oz copper
boards or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See
application note AN-1229 ( SNVA054 ) for more information.
Copyright ? 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM22674
13
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM22674QMRX-ADJ/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 |
| LM22675 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:1A SIMPLE SWITCHER?, Step-Down Voltage Regulator with Precision Enable |
| LM22675MR-5.0 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:1A SIMPLE SWITCHER?, Step-Down Voltage Regulator with Precision Enable |
| LM22675MR-5.0/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 |
| LM22675MR-ADJ | 制造商:Texas Instruments 功能描述:REGULATOR, ADJ. VOLTAGE, 1A 8PSOP 制造商:Texas Instruments 功能描述:REGULATOR, ADJ. VOLTAGE, 1A 8PSOP; Primary Input Voltage:42V; No. of Outputs:1; Output Current:1A; Voltage Regulator Case Style:SOP; No. of Pins:8; Operating Temperature Min:-40C; Operating Temperature Max:125C; SVHC:No SVHC ;RoHS Compliant: Yes |
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