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參數(shù)資料
| 型號： | LM27241MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Synchronous Buck Regulator Controller for Mobile Systems |
| 中文描述： | SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | PLASTIC, TSSOP-20 |
| 文件頁數(shù)： | 17/27頁 |
| 文件大?。?/td> | 1336K |
| 代理商： | LM27241MTC |
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Application Information
(Continued)
Only in the case of the input capacitor, the situation may be
different as is explained next.
INPUT CAPACITOR
In a buck regulator, the input capacitor provides most of the
pulsed current waveform demanded by the switch. However
the DC (average) value of the current through a capacitor in
steady state must be zero. Otherwise, the capacitor would
start accumulating charge every cycle, and that would
clearly not represent a ‘steady state’ by definition.
The equation for the RMS current through the input capacitor
is then
The function D(1-D) has a maxima at D = 0.5. This would
correspond to an input voltage of 5V/0.5 = 10V.And the input
capacitor current at this worst case input voltage would be
The input capacitors must be positioned physically close to
the power stage.
MOSFETs
Selection of FETs for the controller must be done carefully
taking into account efficiency, thermal dissipation and drive
requirements. Typically the component selection is made
according to the most efficient FET for a given price.
When looking for a FET, it is often helpful to compose a
spreadsheet of key parameters. These parameters may be
summarized as ON resistance (R
DS_ON
), gate charge (Q
GS
),
rise and fall times (t
r
and t
f
). The power dissipated in a given
device may then be calculated according to the following
equations:
High-side FET:
P = P
C
+ P
GC
+ P
SW
Where
P
C
= D x (I
OUT2
x R
DS_ON
)
P
GC
= 5V x Q
GS
x f
P
SW
= 0.5 x V
IN
x I
OUT
x (t
r
+ t
f
) x f
Low-side FET:
P = P
C
+ P
GC
Where
P
C
= (1 - D) x (I
OUT2
x R
DS_ON
)
P
GC
= 5V x Q
GS
x f
One will note that the gate charge requirements should be
low to ensure good efficiency. However, if a FET’s gate
charge requirement is too low (less than 8nC), the FET can
turn on spuriously. A good starting point for a 10A load is to
use a high-side and low-side FET each with an on resistance
of 5m
(FET on resistance is a function of temperature,
therefore it is advisable to apply the appropriate correction
factor provided in the FET datasheet), gate to source charge
of 8nC (total gate charge of 36 nC), t
r
= 11ns, t
f
= 47ns, and
temperature coefficient of 1.4. For a 5V input and 1.2V/10A
output (f = 300kHz), this yields a power dissipation of 0.62 W
(high-side FET) and 0.54 W (low-side FET). The efficiency is
then 91%. While the same FET may be used for both the
high side and low side, optimal performance may not be
realized.
20120189
FIGURE 13. Evaluation Board Transient Response
V
= 1.50VDC, V
= 14V
Iout step = 2.5A to 5A, and 5A to 2.5A Load Step.
L
www.national.com
17
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM27241MTC/NOPB | 功能描述:IC REG CTRLR BUCK PWM VM 20TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR) |
| LM27241MTCX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Synchronous Buck Regulator Controller for Mobile Systems |
| LM27241MTCX/NOPB | 功能描述:IC REG CTRLR BUCK PWM VM 20TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:100% 電源電壓:8.2 V ~ 30 V 降壓:無 升壓:無 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:0°C ~ 70°C 封裝/外殼:8-DIP（0.300"，7.62mm） 包裝:管件 產(chǎn)品目錄頁面:1316 (CN2011-ZH PDF) |
| LM27243A E WAF | 制造商:Texas Instruments 功能描述: |
| LM2724A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Speed 3A Synchronous MOSFET Driver |
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