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參數(shù)資料
| 型號： | LM25010MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 42V, 1.0A Step-Down Switching Regulator |
| 中文描述： | 1.5 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封裝： | PLASTIC, TSSOP-14 |
| 文件頁數(shù)： | 9/17頁 |
| 文件大?。?/td> | 776K |
| 代理商： | LM25010MHX |
Control Circuit Overview
(Continued)
The LM25010 requires a minimum of 25 mV of ripple voltage
at the FB pin for stable fixed-frequency operation. If the
output capacitor’s ESR is insufficient additional series resis-
tance may be required (R3 in the Block Diagram).
The LM25010 operates in continuous conduction mode at
heavy load currents, and discontinuous conduction mode at
light load currents. In continuous conduction mode current
always flows through the inductor, never decaying to zero
during the off-time. In this mode the operating frequency
remains relatively constant with load and line variations. The
minimum load current for continuous conduction mode is
one-half the inductor’s ripple current amplitude. The operat-
ing frequency in the continuous conduction mode is calcu-
lated as follows:
(2)
The buck switch duty cycle is equal to:
(3)
Under light load conditions, the LM25010 operates in discon-
tinuous conduction mode, with zero current flowing through
the inductor for a portion of the off-time. The operating
frequency is always lower than that of the continuous con-
duction mode, and the switching frequency varies with load
current. Conversion efficiency is maintained at a relatively
high level at light loads since the switching losses diminish
as the power delivered to the load is reduced. The discon-
tinuous mode operating frequency is approximately:
(4)
where R
L
= the load resistance.
Start-Up Bias Regulator (V
CC
)
A high voltage bias regulator is integrated within the
LM25010. The input pin (VIN) can be connected directly to
line voltages between 6V and 42V. Referring to the block
diagram and the graph of V
vs. V
, when V
is between
6V and the bypass threshold (nominally 8.9V), the bypass
switch (Q2) is on, and V
tracks V
within 100 mV to 150
mV. The bypass switch on-resistance is approximately 50
,
with inherent current limiting at approximately 100 mA.
When VIN is above the bypass threshold, Q2 is turned off,
and V
is regulated at 7V. The V
regulator output current
is limited at approximately 15 mA. When the LM25010 is
shutdown using the RON/SD pin, the V
CC
bypass switch is
shut off, regardless of the voltage at VIN.
When V
IN
exceeds the bypass threshold, the time required
for Q2 to shut off is approximately 2 - 3 μs. The capacitor at
VCC (C3) must be a minimum of 0.47 μF to prevent the
voltage at VCC from rising above its absolute maximum
rating in response to a step input applied at VIN. C3 must be
located as close as possible to the LM25010 pins.
In applications with a relatively high input voltage, power
dissipation in the bias regulator is a concern. An auxiliary
voltage of between 7.5V and 14V can be diode connected to
the VCC pin (D2 in Figure 2) to shut off the VCC regulator,
reducing internal power dissipation. The current required into
the VCC pin is shown in the Typical Performance Character-
istics. Internally a diode connects VCC to VIN requiring that
the auxiliary voltage be less than V
IN
.
The turn-on sequence is shown in Figure 1. When VCC
exceeds the under-voltage lock-out threshold (UVLO) of
5.25V (t1 in Figure 1), the buck switch is enabled, and the SS
pin is released to allow the soft-start capacitor (C6) to charge
up. The output voltage V
is regulated at a reduced level
which increases to the desired value as the soft-start voltage
increases (t2 in Figure 1).
20172716
FIGURE 2. Self Biased Configuration
L
www.national.com
9
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相關代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM25010MHX/NOPB | 功能描述:直流/直流開關轉(zhuǎn)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(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM25010Q0MH | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM25010Q0MH/NOPB | 功能描述:直流/直流開關轉(zhuǎn)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(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| LM25010Q0MHX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:42V, 1.0A Step-Down Switching Regulator |
| LM25010Q0MHX/NOPB | 功能描述:直流/直流開關轉(zhuǎn)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(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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