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參數(shù)資料
| 型號： | LT3748HMS#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO12 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-16/12 |
| 文件頁數(shù)： | 4/30頁 |
| 文件大?。?/td> | 284K |
| 代理商： | LT3748HMS#PBF |
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LT3748
12
3748fa
The current limitation on output power delivery is gen-
erally constrained by transformer saturation current in
higher power applications, although the MOSFET switch
and output diode will need to be rated for the desired
currents, as well. Increasing the peak current on the pri-
mary side of the flyback by reducing the RSENSE resistor
is the primary way to increase output power, and power
delivered increases fairly linearly with current limit as
shown in Figure 2, until parasitic losses begin to dominate.
However, once the saturation current of the transformer
is exceeded the energy coupling between the primary and
the secondary will be reduced and incremental power will
not be delivered to the output. In addition, the primary
inductance will drop, the SENSE pin overcurrent threshold
may trip due to a corresponding rapid rise in current, and
the transformer will have to absorb the energy that is not
transferred through the saturated core, leading to heating.
Some manufacturers may not specify the rated saturation
current but it is a necessary specification when trying to
minimize transformer size and maximize output power
and efficiency. Also necessary for proper design is data
on saturation current over temperature—the saturation
of typical power ferrites may reduce by over 20% from
25°C to 100°C.
The thermal limitation in flyback applications for lower
output voltages will be dominated by losses in the output
diode, with resistive and leakage losses in the transformer
increasing as a percentage basis of loss as the output
voltage is increased. As power levels increase the output
diode and transformer may exceed their rated temperature
specifications. Minimizing RMS output diode current,
selecting a diode with minimal forward drop at expected
currents and minimizing parasitic resistances and leakage
inductance in the transformer will keep those components
below their maximum temperatures while maximizing
efficiency. The following section discussing transformer
selection will further help focus on how to minimize losses
in the output diode.
While quiescent current in the LT3748 itself is low (ap-
proximately 300μA from VIN and 1mA from INTVCC), the
current required to drive the external MOSFET (fSW QG),if
drawn from VINthroughtheLT3748INTVCCLDO,dissipates
(VIN – INTVCC) fSW QG. If that power is high enough to
cause significant heating of the LT3748 the current may
need to be drawn from a third winding. Doing so will push
all thermal limitations outside of the LT3748.
Selecting a Transformer
Transformer specification and design is perhaps the most
critical part of successfully applying the LT3748. In addition
to the usual list of caveats dealing with high frequency
isolated power supply transformer design, the following
information should be carefully considered.
First and most importantly, since the voltage on the sec-
ondary side of the transformer is inferred by the voltage
sampled on the primary, the transformer turns ratio must
be tightly controlled to ensure a consistent output volt-
age. A tolerance of ±5% in turns ratio from transformer to
transformer could result in a variation of more than ±5% in
output regulation. Fortunately, most magnetic component
manufacturers are capable of guaranteeing a turns ratio
tolerance of 1% or better.
Linear Technology has worked with several leading mag-
netic component manufacturers to produce predesigned
flyback transformers for use with the LT3748. Table 1
shows the details of several of these transformers.
APPLICATIONS INFORMATION
INPUT VOLTAGE (V)
0
MAXIMUM
OUTPUT
POWER
(W)
30
40
50
80
3748 F02
20
10
0
20
40
60
100
ILIM = 3A
ILIM = 2A
ILIM = 1A
Figure 2. Maximum Output Power at 12VOUT
with 150V VDS(MAX) and ILIM = 1A, 2A, 3A
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LT3748HMSTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748IMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP 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:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 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 ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP 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:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 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 ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMSPBF | 制造商:Linear Technology 功能描述:100V Isolated Flyback Controller MSOP16 |
| LT3748IMSTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100V Isolated Flyback Controller |
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