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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)： | 8/30頁 |
| 文件大?。?/td> | 284K |
| 代理商： | LT3748HMS#PBF |
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LT3748
16
3748fa
APPLICATIONS INFORMATION
ring beyond that expected reverse voltage. An RC snubber
or RCD clamp may be implemented to reduce the voltage
spike if it is desirable to use a lower reverse voltage diode.
Secondary Leakage Inductance
In addition to the previously described effects of leakage
inductance in general, leakage inductance on the secondary
in particular exhibits an additional phenomena. It forms an
inductive divider on the transformer secondary that effec-
tively reduces the size of the primary-referred flyback pulse
used for feedback. This will increase the output voltage
target by a similar percentage. Note that, unlike leakage
spike behavior, this phenomena is load independent. To the
extent that the secondary leakage inductance is a constant
percentage of mutual inductance (over manufacturing
Although it typically does not decrease efficiency, leakage
inductance energy that would normally have been dis-
sipated in the switch or transformer is also dissipated in
the RC snubber resistor and can be calculated as:
PSNUBBER = fSW LLEAK ILIM2/2
An RCD clamp, shown in Figure 7, also prevents the
leakage inductance spike from exceeding the breakdown
voltage of the MOSFET switch. In most applications, there
will be a very fast voltage spike caused by a slow clamp
diode. Once the diode clamps, the leakage inductance
current is absorbed by the clamp capacitor. This period
should not last longer than 200ns so as not to interfere
with the output regulation. The clamp diode turns off after
the leakage inductance energy is absorbed and the switch
voltage is then equal to:
VDS = VIN + NPS (VOUT + VF(DIODE))
Schottky diodes are typically the best choice for use in a
snubber, but some PN diodes can be used if they turn on
fast enough to limit the leakage inductance spike. Figures 8
and 9 show the waveform at the drain of the MOSFET
switch for the 48V output application shown in Figure 17
at maximum rated load and maximum input voltage with
an RC snubber and RCD clamp, respectively. Both solu-
tions limit the leakage spike to less than 190V, below the
200V VDS(MAX) rating of the Si7464DP MOSFET.
Figure 7. RCD Clamp
Figure 8. Waveform of MOSFET Drain During Normal Operation
of Figure 17 with RC Snubber (as Drawn)
3748 F07
LLEAK
VIN
VOUT+
VOUT–
GATE
NMOS
D
R
C
+
Figure 9. Waveform of MOSFET Drain During Normal Operation
of Figure 17 Using RCD Clamp with Central Semiconductor
CMR1U-02M-LTC Instead of RC Snubber
TIME (ns)
0
DRAIN
VOLTAGE
(V)
40
80
120
50
100
150
200
3748 F08
250
160
200
20
60
100
140
180
300
VIN = 96V
VOUT = 48V
IOUT = 0.5A
R = 66Ω
C = 150pF
TIME (ns)
0
DRAIN
VOLTAGE
(V)
40
80
120
50
100
150
200
3748 F08
250
160
200
20
60
100
140
180
300
VIN = 96V
VOUT = 48V
IOUT = 0.5A
R = 4.99k
C = TDK 0.22μF 250V
D = CMR1U-02M-LTC
Leakage Inductance and Output Diode Stress
The output diode may also see increased reverse voltage
stresses from leakage inductance. While it nominally sees
a reverse voltage of the input voltage divided by the wind-
ings ratio plus the output voltage when the MOSFET power
switch turns on, the capacitance on the output diode and
the leakage inductance will cause an LC tank which may
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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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