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參數資料
| 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： | 15/15頁 |
| 文件大?。?/td> | 662K |
| 代理商： | LM5008MMXEP |
High Voltage Start-Up Regulator (Continued)
Regulation Comparator
The feedback voltage at FB is compared to an internal 2.5V
reference. In normal operation (the output voltage is regu-
lated), an on-time period is initiated when the voltage at FB
falls below 2.5V. The buck switch will stay on for the on-time,
causing the FB voltage to rise above 2.5V. After the on-time
period, the buck switch will stay off until the FB voltage again
falls below 2.5V. During start-up, the FB voltage will be below
2.5V at the end of each on-time, resulting in the minimum
off-time of 300 ns. Bias current at the FB pin is nominally 100
nA.
Over-Voltage Comparator
The feedback voltage at FB is compared to an internal
2.875V reference. If the voltage at FB rises above 2.875V
the on-time pulse is immediately terminated. This condition
can occur if the input voltage, or the output load, change
suddenly. The buck switch will not turn on again until the
voltage at FB falls below 2.5V.
On-Time Generator and Shutdown
The on-time for the LM5008EP is determined by the R
ON
resistor, and is inversely proportional to the input voltage
(Vin), resulting in a nearly constant frequency as Vin is
varied over its range. The on-time equation for the
LM5008EP is:
T
ON =1.25x10
-10 xR
ON /VIN
(2)
See Figure 3.R
ON should be selected for a minimum on-time
(at maximum V
IN) greater than 400 ns, for proper current
limit operation. This requirement limits the maximum fre-
quency for each application, depending on V
IN and VOUT.
See Figure 4.
The LM5008EP can be remotely disabled by taking the
R
ON/SD pin to ground. See Figure 11. The voltage at the
R
ON/SD pin is between 1.5 and 3.0 volts, depending on Vin
and the value of the R
ON resistor.
20187606
FIGURE 10. Self Biased Configuration
20187607
FIGURE 11. Shutdown Implementation
LM5008EP
www.national.com
9
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM5008SD | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SD/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDC | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDC/NOPB | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM5008SDCX | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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