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參數(shù)資料
| 型號： | LM5008MMXEP |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.61 A SWITCHING REGULATOR, 600 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 14/15頁 |
| 文件大?。?/td> | 662K |
| 代理商： | LM5008MMXEP |
Hysteretic Control Circuit
Overview (Continued)
the end of the off-time. The next on-time period starts when
the voltage at FB falls below the internal reference - until
then the inductor current remains zero. In this mode the
operating frequency is lower than in continuous conduction
mode, and varies with load current. Therefore at light loads
the conversion efficiency is maintained, since the switching
losses reduce with the reduction in load and frequency. The
discontinuous operating frequency can be calculated as fol-
lows:
where R
L = the load resistance
In continuous conduction mode, current flows continuously
through the inductor and never ramps down to zero. In this
mode the operating frequency is greater than the discontinu-
ous mode frequency and remains relatively constant with
load and line variations. The approximate continuous mode
operating frequency can be calculated as follows:
(1)
The output voltage (V
OUT) can be programmed by two ex-
ternal resistors as shown in Figure 1. The regulation point
can be calculated as follows:
V
OUT =2.5x(R1+R2)/R2
All hysteretic regulators regulate the output voltage based on
ripple voltage at the feedback input, requiring a minimum
amount of ESR for the output capacitor C2. A minimum of
25mV to 50mV of ripple voltage at the feedback pin (FB) is
required for the LM5008EP. In cases where the capacitor
ESR is too small, additional series resistance may be re-
quired (R3 in Figure 1).
For applications where lower output voltage ripple is re-
quired the output can be taken directly from a low ESR
output capacitor, as shown in Figure 9. However, R3 slightly
degrades the load regulation.
High Voltage Start-Up Regulator
The LM5008EP contains an internal high voltage startup
regulator. The input pin (V
IN) can be connected directly to the
line voltages up to 95 Volts, with transient capability to 100
volts. The regulator is internally current limited to 9.5mA at
V
CC. Upon power up, the regulator sources current into the
external capacitor at V
CC (C3). When the voltage on the VCC
pin reaches the under-voltage lockout threshold of 6.3V, the
buck switch is enabled.
In applications involving a high value for V
IN, where power
dissipation in the V
CC regulator is a concern, an auxiliary
voltage can be diode connected to the V
CC pin. Setting the
auxiliary voltage to 8.0 -14V will shut off the internal regula-
tor, reducing internal power dissipation. See Figure 10. The
current required into the V
CC pin is shown in Figure 2.
20187605
FIGURE 9. Low Ripple Output Configuration
LM5008EP
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM5008SD | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SD/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDC | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDC/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDCX | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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