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參數(shù)資料
| 型號： | LM5010MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 1.5 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO14 |
| 封裝： | TSSOP-14 |
| 文件頁數(shù)： | 10/19頁 |
| 文件大?。?/td> | 453K |
| 代理商： | LM5010MHX |
Hysteretic Control Circuit
Overview
(Continued)
Typically when the load current increases suddenly, the off-
times are temporarily at the minimum of 265 ns. Once regu-
lation is established, the off-time resumes its normal value.
The output voltage is set by two external resistors (R1, R2).
The regulated output voltage is calculated as follows:
V
OUT
= 2.5V x (R1 + R2) / R2
Output voltage regulation is based on ripple voltage at the
feedback input, requiring a minimum amount of ESR for the
output capacitor C2. The LM5010 requires a minimum of 25
mV of ripple voltage at the FB pin. In cases where the
capacitor’s ESR is insufficient additional series resistance
may be required (R3 in
Figure 1
).
When in regulation, the LM5010 operates in continuous
conduction mode at heavy load currents and discontinuous
conduction mode at light load currents. In continuous con-
duction mode current always flows through the inductor,
never reaching 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 approximate operating frequency is calcu-
lated as follows:
(1)
(2)
The buck switch duty cycle is approximately equal to:
(3)
At low load current, the circuit operates in discontinuous
conduction mode, during which the inductor current ramps
up from zero to a peak during the on-time, then ramps back
to zero before the end of the off-time. The next on-time
period starts when the voltage at FB falls below the refer-
ence - until then the inductor current remains zero, and the
load current is supplied by the output capacitor (C2). In this
mode the operating frequency is lower than in continuous
conduction mode, and varies with load current. Conversion
efficiency is maintained at light loads since the switching
losses reduce with the reduction in load and frequency. The
approximate discontinuous operating frequency can be cal-
culated as follows:
(4)
where R
L
= the load resistance.
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.
Start-up Regulator (V
CC
)
The startup regulator is integral to the LM5010. The input pin
(V
) can be connected directly to line voltages up to 75V.
The V
output is regulated at 7.0V,
±
6%, and is current
limited to 10 mA. Upon power up the regulator sources
current into the external capacitor at V
(C3). With a 0.1 μF
capacitor at V
, approximately 58 μs are required for the
V
voltage to reach the under-voltage lockout threshold
(UVLO) of 5.8V (t1 in
Figure 8
), at which time the buck switch
is enabled, and the softstart pin is released to allow the
softstart capacitor (C6) to charge up. V
then increases to
its regulated value as the softstart voltage increases (t2 in
Figure 8
).
The minimum input operating voltage is determined by the
regulator’s dropout voltage, the V
UVLO falling threshold
(
)
5.65V), and the frequency. When V
falls below the
falling threshold the V
UVLO activates to shut off the buck
switch and ground the softstart pin. If V
is externally
loaded, the minimum input voltage increases since the out-
put impedance at V
is
)
140
at low V
. See Figures 2
and 3. In applications involving a high value for V
where
power dissipation in the startup regulator is a concern, an
auxiliary voltage can be diode connected to the V
pin
(
Figure 10
). Setting the auxiliary voltage to between 7.5V
and 14V shuts off the internal regulator, reducing internal
power dissipation. The current required into the V
CC
pin is
shown in
Figure 4
. Internally a diode connects V
CC
to V
IN
.
20119915
FIGURE 9. Low Ripple Output Configuration
L
www.national.com
10
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|---|---|
| LM5010MHX/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 |
| LM5010SD | 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 |
| LM5010SD/MEY8 | 制造商:Texas Instruments 功能描述: |
| LM5010SD/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 HIGH VOLTAGE 1A STEP DOWN SWITCHING 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 安裝風格:SMD/SMT |
| LM5010SDX | 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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