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參數(shù)資料
| 型號(hào)： | LM5008 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | High Voltage (100V) Step Down Switching Regulator |
| 中文描述： | 高電壓（100V的）降壓開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 8/15頁 |
| 文件大?。?/td> | 278K |
| 代理商： | LM5008 |
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
= 2.5 x (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 LM5008. In cases where the capacitor ESR
is too small, additional series resistance may be required
(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 LM5008 contains an internal high voltage startup regu-
lator. 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 exter-
nal capacitor at V
CC
(C3). When the voltage on the V
CC
pin
reaches the under-voltage lockout threshold of 6.3V, the
buck switch is enabled.
In applications involving a high value for V
, where power
dissipation in the V
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
.
20097905
FIGURE 9. Low Ripple Output Configuration
L
www.national.com
8
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM5008_09 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Voltage (100V) Step Down Switching Regulator |
| LM5008A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:100V, 350 mA Constant On-Time Buck Switching Regulator |
| LM5008AEVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM5008A EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| LM5008AMM | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:100V, 350 mA Constant On-Time Buck Switching Regulator |
| LM5008AMM/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 100V,350Ma Buck Reg 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(fēng)格:SMD/SMT |
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