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參數(shù)資料
| 型號： | LM5005MH |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Voltage 2.5 Amp Buck Regulator |
| 中文描述： | 4.25 A SWITCHING REGULATOR, 525 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | TSSOP-20 |
| 文件頁數(shù)： | 15/21頁 |
| 文件大?。?/td> | 774K |
| 代理商： | LM5005MH |
Application Information
EXTERNAL COMPONENTS
The procedure for calculating the external components is
illustrated with the following design example. The Bill of
Materials for this design is listed in Table1. The circuit shown
in Figure 1 is configured for the following specifications:
V
OUT
= 5V
V
IN
= 7V to 75V
Fs = 300 KHz
Minimum load current (for CCM) = 250 mA
Maximum load current = 2.5A
R3 (R
T
)
R
sets the oscillator switching frequency. Generally, higher
frequency applications are smaller but have higher losses.
Operation at 300KHz was selected for this example as a
reasonable compromise for both small size and high effi-
ciency. The value of R
for 300KHz switching frequency can
be calculated as follows:
The nearest standard value of 21 k
was chosen for RT.
L1
The inductor value is determined based on the operating
frequency, load current, ripple current, and the minimum and
maximum input voltage (V
IN(min)
, V
IN(max)
).
To keep the circuit in continuous conduction mode (CCM),
the maximum ripple current I
should be less than twice
the minimum load current, or 0.5 Ap-p. Using this value of
ripple current, the value of inductor (L1) is calculated using
the following:
This procedure provides a guide to select the value of L1.
The nearest standard value (33 μH) will be used. L1 must be
rated for the peak current (I
PK+
) to prevent saturation. During
normal loading conditions, the peak current occurs at maxi-
mum load current plus maximum ripple. During an overload
condition the peak current is limited to 3.5A nominal (4.25A
maximum). The selected inductor (see Table 1) has a con-
servative 6.2 Amp saturation current rating. For this manu-
facturer, the saturation rating is defined as the current nec-
essary for the inductance to reduce by 30%, at 20C.
C3 (C
RAMP
)
With the inductor value selected, the value of C3 (C
RAMP
)
necessary for the emulation ramp circuit is:
C
RAMP
= L x 10
-5
Where L is in Henrys
With L1 selected for 33μH the recommended value for C3 is
330pF.
C9, C10
The output capacitors C9 and C10 smooth the inductor
ripple current and provide a source of charge for transient
loading conditions. For this design a 22μF ceramic capacitor
and a 150μF SP organic capacitor were selected. The ce-
ramic capacitor provides ultra low ESR to reduce the output
ripple voltage and noise spikes, while the SP capacitor pro-
vides a large buck capacitance in a small volume for tran-
sient loading conditions. An approximation for the output
ripple voltage is:
D1
A Schottky type re-circulating diode is required for all
LM5005 applications. Ultra-fast diodes are not recom-
mended and may result in damage to the IC due to reverse
recovery current transients. The near ideal reverse recovery
characteristics and low forward voltage drop are particularly
important diode characteristics for high input voltage and low
output voltage applications common to the LM5005. The
reverse recovery characteristic determines how long the
current surge lasts each cycle when the buck switch is
turned on. The reverse recovery characteristics of Schottky
diodes minimize the peak instantaneous power in the buck
switch occurring during turn-on each cycle. The resulting
switching losses of the buck switch are significantly reduced
when using a Schottky diode. The reverse breakdown rating
should be selected for the maximum V
IN
, plus some safety
margin.
The forward voltage drop has a significant impact on the
conversion efficiency, especially for applications with a low
output voltage. “Rated” current for diodes vary widely from
various manufactures. The worst case is to assume a short
circuit load condition. In this case the diode will carry the
output current almost continuously. For the LM5005 this
current can be as high as 3.5A. Assuming a worst case 1V
drop across the diode, the maximum diode power dissipation
can be as high as 3.5W. For the reference design a 100V
Schottky in a DPAK package was selected.
C1, C2
The regulator supply voltage has a large source impedance
at the switching frequency. Good quality input capacitors are
necessary to limit the ripple voltage at the VIN pin while
supplying most of the switch current during the on-time.
20161910
FIGURE 7. Inductor Current Waveform
L
www.national.com
15
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| LM5005MH/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 2.5A Integrated Buck Regulator 75V 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 |
| LM5005MHX | 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(fēng)格:SMD/SMT |
| LM5005MHX/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(fēng)格:SMD/SMT |
| LM5006 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Evaluation Board provides the design engineer with a fully functional |
| LM5006EVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM5006 EVAL BOARD RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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