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參數(shù)資料
| 型號： | LM27402MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 1350 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 5 X 4.40 MM, 0.90 MM HEIGHT, 0.65 MM PITCH, ETSSOP-16 |
| 文件頁數(shù)： | 14/32頁 |
| 文件大?。?/td> | 653K |
| 代理商： | LM27402MHX |
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P
CND_LS is the conduction loss of the low-side FET during the
1-D cycle when current is flowing through the on-resistance
of the FET. R
DS(ON)_LS () is the drain to source resistance.
P
D is the deadtime power loss due to the body diode drop of
the low-side FET. T
deadtime (s) is the total deadtime.
P
RR is the reverse recovery charge power loss. QRR (C) is the
total reverse recovery charge usually specified in the FET
datasheet. P
TOT_LS is the total power dissipation of the low-
side FET.
Gate Charge Loss
A finite amount of gate charge is required in order to switch
the high-side and low-side FETs. This gate charge is contin-
uously charging the FETs during every switching cycle and
appears as a constant current flowing into the controller from
the input supply. The next equation describes the power loss
due to the gate charge.
P
QG is the total gate charge power loss, QGHS (C) and QGLS
(C) are the high-side and low-side FET gate charges respec-
tively, and can be found in the FET datasheets,V
IN (V) is the
input voltage, and f
SW (Hz) is the switching frequency.
Input and Output Capacitor ESR Losses
Both the input and output capacitors are subject to steady
state AC current and must be taken into consideration when
calculating power losses. The next equation shown is the in-
put capacitor ESR power loss.
The input capacitor power loss equation includes the effective
series resistance or R
ESR_IN () of the input capacitor. The
power loss due to the ESR of the output capacitor is:
The output capacitor power loss equation includes the peak
to peak inductor current,
ΔI
L(A), and the effective series re-
sistance or R
ESR () of the output capacitor.
Inductor Losses
The losses due to the inductor are caused primarily by the
DCR. The next equation calculates the inductor DCR power
loss.
P
DCR is the total power loss of the Inductor. A self heating
coefficient of 1.2 is included in this equation to approximate
the effects of the copper temperature coefficient approxi-
mately equal to 3900ppm/°C. R
DCR () is the inductor DC
resistance.
Controller Losses
The controller loss remains constant and contributes to a very
small loss of power. The quiescent current is the main factor
in terms of power loss attributed to the controller and it re-
mains constant at 4 mA. The quiescent current power loss
equation is:
The controller I
Q power loss equation includes the IQ current
(4 mA) and input voltage V
IN (V).
It is also important to calculate the power dissipated in the
controller itself due to the gate charge current flowing from
VIN to the output of the LDO (VDD). The gate charge current
essentially passes through a resistance dropping the input
voltage VIN to the LDO voltage (4.5V). This can cause the
controller to operate at an elevated temperature since it must
dissipate the power of the LDO pass device. The next equa-
tion calculates the power dissipated by the internal LDO of the
controller.
P
LDO is the power dissipated in the LDO, QGHS (C) and
Q
GLS are the high-side and low-side FET gate charges, re-
spectively, and can be found in the FET datasheets.
Overall Efficiency
After calculating the losses, the efficiency can then be calcu-
lated using:
PCB LAYOUT CONSIDERATIONS
After selecting the correct components, PCB layout is another
crucial step in optimizing a buck regulator. The layout must
be able to handle large DC and AC currents, minimize switch-
node noise, and spread heat. The following layout guidelines
and tips will help increase the chances of a successful design
and should be taken seriously during the layout process.
Input and Output Capacitor Layout
A buck regulator is a switching converter with switched cur-
rents and voltages. The high di/dt and dv/dt nature of buck
switching calls for careful layout of decoupling capacitors. The
next figures shows the switching currents for the D and 1-D
intervals of a buck regulator.
30092665
FIGURE 19. Power Flow
During the high-side FET on time, the AC component of the
input current is supplied by the input capacitor. Due to the high
di/dt nature of this current, it is essential that the input capac-
itor is closely coupled to the drain of the high-side FET to
minimize any parasitic inductance. The output capacitor re-
21
www.national.com
LM27402
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM27402MHX/NOPB | 功能描述:DC/DC 開關控制器 High Perf Sync Buck Cntrlr RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM27402SQ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM27402SQ/NOPB | 功能描述:DC/DC 開關控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| LM27402SQEVAL/NOPB | 功能描述:電源管理IC開發(fā)工具 LM27402SQ 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 |
| LM27402SQX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Performance Synchronous Buck Controller with DCR Current Sensing |
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