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參數(shù)資料
| 型號： | L6997 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | STEP DOWN CONTROLLER FOR LOW VOLTAGE OPERATIONS |
| 中文描述： | 降壓控制器低電壓運(yùn)作 |
| 文件頁數(shù)： | 16/23頁 |
| 文件大小： | 291K |
| 代理商： | L6997 |
L6997
16/23
3
V
IN
= 3.3V, ±10% V
OUT
= 1.25V I
OUT
= 5A F
SW
= 270kHz
STEP BY STEP DESIGN
3.1 Input capacitor.
A pulsed current (with zero average value) flows through the input capacitor of a buck converter. The AC com-
ponent of this current is quite high and dissipates a considerable amount of power on the ESR of the capacitor:
Eq 17
The RMS current, which the capacitor must provide, is given by:
Eq 18
Neglecting the last term, the equation reduces to:
Eq 19
which maximum value corresponds to to
δ
= 1/2.
ICIN
RMS
, has a maximum equal to
δ
= 1/2 (@ VIN = 2×VOUT, that is, 50% duty cycle). The input, therefore,
should be selected for a RMS ripple current rating as high as half the respective maximum output current.
Electrolytic capacitors are the most used cause are the cheapest ones and are available with a wide range of
RMS current ratings. The only drawback is that, considering a requested ripple current rating, they are physically
larger than other capacitors. Very good tantalum capacitors are coming available, with very low ESR and small
size. The only problem is that they occasionally can burn if subjected to very high current during the charge. So,
it is better avoid this type of capacitors for the input filter of the device. In fact, they can be subjected to high
surge current when connected to the power supply. If available for the requested value and voltage rating, the
ceramic capacitors have usually a higher RMS current rating for a given physical dimension (due to the very low
ESR). The drawback is the quite high cost. Possible solutions:
With our parameter from the equation 3 it is found:
Icin
rms
= 2.42A
3.2 Inductor
To define the inductor, it is necessary to determine firstly the inductance value. Its minimum value is given by:
Eq 20
where RF is given from
I/I
OUT
(basically it is around 30%).
10
μ
F
22
μ
F
C34Y5U1E106ZTE12 TOKIN
JMK325BJ226MM
TAIYO-YUDEN
ECJ4XF0J476Z
PANASONIC
C3225X5R0J476M
TDK
47
μ
F
33
μ
F
P
CIN
ESR
CIN
Iout
2
Vin
Vin
Vin
2
Vout
–
(
)
=
Icin
rms
Iout
2
δ
1
δ
–
(
)
12
------
I
L
(
)
2
+
=
Icin
rms
Iout
δ
1
δ
–
(
)
=
Lmin
V
Vin
)
F
SW
I
out
RF Vin
max
------------------------------------------–
≥
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| L6997-28 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
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| L6997-9 | 制造商:Johanson Manufacturing 功能描述:TUNING ELEMENT |
| L6997D | 功能描述:DC/DC 開關(guān)控制器 Adjustable Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)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(fēng)格: 封裝 / 箱體:CPAK |
| L6997DTR | 功能描述:DC/DC 開關(guān)控制器 Adjustable Step-Down RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)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(fēng)格: 封裝 / 箱體:CPAK |
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