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| 型号： | LM22673MRX-5.0/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 8/27页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 3A 8PSOP |
| 产品培训模块： | SIMPLE SWITCHER® Regulators LM315x & LM2267x SIMPLE SWITCHER® and WEBENCH |
| 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： | 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 Width）裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-PSOP-EP |
| 配用： | 551600236-001-ND - WEBENCH BUILD IT LM2267X 8-PSOP LM22673EVAL/NOPB-ND - BOARD EVALUATION FOR LM22673 |
| 其它名称： | LM22673MRX-5.0 |
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SNVS586N – SEPTEMBER 2008 – REVISED APRIL 2013
Duty-Cycle Limits
Ideally the regulator would control the duty cycle over the full range of zero to one. However due to inherent
delays in the circuitry, there are limits on both the maximum and minimum duty cycles that can be reliably
controlled. This in turn places limits on the maximum and minimum input and output voltages that can be
converted by the LM22673. A minimum on-time is imposed by the regulator in order to correctly measure the
switch current during a current limit event. A minimum off-time is imposed in order the re-charge the bootstrap
capacitor. The following equation can be used to determine the approximate maximum input voltage for a given
output voltage:
(1)
Where F sw is the switching frequency and T ON is the minimum on-time; both found in the Electrical
Characteristics table. Nominal values should be used. The worst case is lowest output voltage. If this input
voltage is exceeded, the regulator will skip cycles, effectively lowering the switching frequency. The
consequences of this are higher output voltage ripple and a degradation of the output voltage accuracy.
The second limitation is the maximum duty cycle before the output voltage will "dropout" of regulation. The
following equation can be used to approximate the minimum input voltage before dropout occurs:
(2)
The values of T OFF and R DS(ON) are found in the Electrical Characteristics table. The worst case here is largest
load. In this equation, R L is the D.C. inductor resistance. Of course, the lowest input voltage to the regulator must
not be less than 4.5V (typ.).
Current Limit
The LM22673 has current limiting to prevent the switch current from exceeding safe values during an accidental
overload on the output. This peak current limit is found in the Electrical Characteristics table under the heading of
I CL . The maximum load current that can be provided, before current limit is reached, is determined from the
following equation:
(3)
Where L is the value of the power inductor.
When the LM22673 enters current limit, the output voltage will drop and the peak inductor current will be fixed at
I CL at the end of each cycle. The switching frequency will remain constant while the duty cycle drops. The load
current will not remain constant, but will depend on the severity of the overload and the output voltage.
For very severe overloads ("short-circuit"), the regulator changes to a low frequency current foldback mode of
operation. The frequency foldback is about 1/5 of the nominal switching frequency. This will occur when the
current limit trips before the minimum on-time has elapsed. This mode of operation is used to prevent inductor
current "run-away", and is associated with very low output voltages when in overload. The following equation can
be used to determine what level of output voltage will cause the part to change to low frequency current foldback:
(4)
Where F sw is the normal switching frequency and V in is the maximum for the application. If the overload drives
the output voltage to less than or equal to V x , the part will enter current foldback mode. If a given application can
drive the output voltage to ≤ V x , during an overload, then a second criterion must be checked. The next equation
gives the maximum input voltage, when in this mode, before damage occurs:
(5)
8
Product Folder Links: LM22673
Copyright ? 2008–2013, Texas Instruments Incorporated
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相关代理商/技术参数 |
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|---|---|
| LM22673MRX-ADJ | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Inv/Step Down 4.5V to 42V 8-Pin PSOP EP T/R |
| LM22673MRX-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 |
| LM22673QMR-5.0/NOPB | 制造商:Texas Instruments 功能描述:IC REG BUCK 5V 3A 8SOPWRPAD 制造商:Texas Instruments 功能描述:42V, 3A SIMPLE SWITCHER Step-Down Volta |
| LM22673QMR-ADJ/NOPB | 制造商:Texas Instruments 功能描述:IC REG BUCK ADJ 3A 8SOPWRPAD |
| LM22673QMRE-5.0/NOPB | 制造商:Texas Instruments 功能描述:IC REG BUCK 5V 3A 8SOPWRPAD 制造商:Texas Instruments 功能描述:42V, 3A SIMPLE SWITCHER Step-Down Volta |
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