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| 型号： | LM22674QMRX-5.0/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 11/22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
INDUCTOR
The inductor value is determined based on the load current, ripple current, and the minimum and maximum input
voltages. To keep the application in continuous conduction mode (CCM), the maximum ripple current, I RIPPLE ,
should be less than twice the minimum load current. The general rule of keeping the inductor current peak-to-
peak ripple around 30% of the nominal output current is a good compromise between excessive output voltage
ripple and excessive component size and cost. Using this value of ripple current, the value of inductor, L, is
calculated using the following formula:
where
?
F sw is the switching frequency and V in should be taken at its maximum value, for the given application.
(10)
The above formula provides a guide to select the value of the inductor L; the nearest standard value will then be
used in the circuit.
Once the inductor is selected, the actual ripple current can be found from the equation shown below:
(11)
Increasing the inductance will generally slow down the transient response but reduce the output voltage ripple.
Reducing the inductance will generally improve the transient response but increase the output voltage ripple.
The inductor must be rated for the peak current, I PK , in a given application, to prevent saturation. During normal
loading conditions, the peak current is equal to the load current plus 1/2 of the inductor ripple current.
During an overload condition, as well as during certain load transients, the controller may trip current limit. In this
case the peak inductor current is given by I CL , found in the Electrical Characteristics table. Good design practice
requires that the inductor rating be adequate for this overload condition. If the inductor is not rated for the
maximum expected current, it can saturate resulting in damage to the LM22674 and/or the power diode.
INPUT CAPACITOR
The input capacitor selection is based on both input voltage ripple and RMS current. Good quality input
capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the regulator current
during switch on-time. Low ESR ceramic capacitors are preferred. Larger values of input capacitance are
desirable to reduce voltage ripple and noise on the input supply. This noise may find its way into other circuitry,
sharing the same input supply, unless adequate bypassing is provided. A very approximate formula for
determining the input voltage ripple is shown below:
where
?
V ri is the peak-to-peak ripple voltage at the switching frequency.
(12)
Another concern is the RMS current passing through this capacitor. The following equation gives an
approximation to this current:
(13)
The capacitor must be rated for at least this level of RMS current at the switching frequency.
All ceramic capacitors have large voltage coefficients, in addition to normal tolerances and temperature
coefficients. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum
capacitance up to the desired value. This may also help with RMS current constraints by sharing the current
among several capacitors. Many times it is desirable to use an electrolytic capacitor on the input, in parallel with
the ceramics. The moderate ESR of this capacitor can help to damp any ringing on the input supply caused by
long power leads. This method can also help to reduce voltage spikes that may exceed the maximum input
voltage rating of the LM22674.
Copyright ? 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM22674
11
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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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