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參數(shù)資料
| 型號： | LT1432CN8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 5V High Efficiency Step-Down Switching Regulator Controller |
| 中文描述： | SWITCHING CONTROLLER, PDIP8 |
| 封裝： | PLASTIC, DIP-8 |
| 文件頁數(shù)： | 18/28頁 |
| 文件大?。?/td> | 611K |
| 代理商： | LT1432CN8 |
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18
LT1432
U
S
A
O
PPLICATI
IU
U
in mind when adding an output filter is that if the filter
capacitor is small, it may allow large output perturbations
if large load transients occur. This effect should be care-
fully checked before finalizing any filter design. For more
details on output filters, consult Application Notes 19
and 44.
Output Capacitor
To avoid overheating, the output capacitor must be large
enough to handle the ripple current generated by the main
inductor. It must also have low enough effective series
resistance (ESR) to meet output ripple voltage require-
ments. RMS ripple current in the output capacitor is given
by:
(
I
V
V – V
3.5V (f)(L)
RIPPLE(RMS)
OUT
OUT
=
)
(use maximum V
IN
)
For V
IN
= 15V, f = 60kHz, L = 50
μ
H,
I
5(15 – 5)
3.5 15 60E
50E
0.32A
RIPPLE(RMS)
3
–6
RMS
=
=
Ripple current ratings are specified on capacitors intended
for switching applications, but the number is subject to
much manipulation. The high frequency number is greater
than the low frequency value, and theoretically one can
multiply the ripple number by significant amounts at
temperatures below the typical 85
°
C or 105
°
C rating point.
The problem is that the ripple ratings are already unreal-
istically high at the rated temperature because they are
typically based on a 2000 hour life. I assume this is an
unacceptable lifetime number, so the ripple rating must be
reduced to extend life. The net result of all this fiddling
with the numbers is generally a headache, but it is prob-
ably conservative to use the stated high frequency rating
at temperatures below 60
°
C for a 105
°
C capacitor, and
assume that the unit will last at least 50,000 hours.
Remember to factor in actualoperating time at elevated
temperatures. Laptop computers, for instance, might be
expected to operate no more than four hours a day on
Input Supply Bypass Capacitor
The input capacitor on a step-down (buck) switching
regulator must handle switching currents with a peak-to-
peak amplitude at least equal to the output current. The
RMS value of capacitor current is approximately equal to:
(
I
I
V
V – V
V
IN
RMS
OUT
OUT
OUT
1/2
]
=
)
[
This formula has a maximum at V
IN
= 2V
OUT
, where I
RMS
is equal to I
OUT
/2. This simple worst case condition is
commonly used for design because even significant de-
viations from V
IN
/2 do not offer much relief. A 2A output
(transient loads can be ignored if they last less than 30
seconds) therefore requires an input capacitor with a 1A
ripple current rating. Don’t cheat and read the output
capacitor section for details on ripple current! The input
capacitor may well be the largest component in the switch-
ing regulator. Spend time playing with aspect ratios of
various capacitor families and don’t hesitate to parallel
several units to achieve a low profile.
Output Voltage Ripple
Output voltage ripple is determined by the main inductor
value, switching frequency, input voltage, and the ESR
(effective series resistance) of the output capacitor. The
following formula assumes a load current high enough to
establish continuous current in the inductor.
Output Ripple Voltage = V
p-p
(
V (f)(L)
=
)(
)
V
V – V
ESR
V
OUT
OUT
p-p
With V
IN
= 12V, ESR = 0.05
, f = 60kHz, and L = 50
μ
H
5(12– 5)(0.05)
p-p
3
( )
If low output ripple voltage is a requirement, larger output
capacitors and/or inductors may not be the answer. An
output filter can be added at modest cost which will
attenuate ripple much more space-effectively than an
oversized output capacitor or inductor. The thing to keep
V
50E
= 48.6mV
–6
p-p
=
相關PDF資料 |
PDF描述 |
|---|---|
| LT1432CN8-3.3 | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LT1432CN8-3.3 | 功能描述:IC REG CTRLR BUCK PWM 8-DIP RoHS:否 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) |
| LT1432CS8 | 制造商:Linear Technology 功能描述: |
| LT1432CS8-3.3 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:3.3V High Efficiency Step-Down Switching Regulator Controller |
| LT1435 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:4.5A, 500kHz Step-Down Switching Regulator |
| LT1436 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:4.5A, 500kHz Step-Down Switching Regulator |
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