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参数资料
| 型号： | LT3748EMS#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO12 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16/12 |
| 文件页数： | 7/30页 |
| 文件大小： | 284K |
| 代理商： | LT3748EMS#TRPBF |
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LT3748
15
3748fa
APPLICATIONS INFORMATION
Saturation Current
As discussed earlier in the Maximum Output Power sec-
tion, because the core of the transformer is being used for
energy storage in a flyback, the current in the transformer
windings should not exceed their rated saturation current
as energy injected once the core is saturated will not be
transferred to the secondary and will instead be dissipated
in the core. Information on saturation current should be
provided by the transformer manufacturers and Table 1
lists the saturation current of the transformers designed
for use with the LT3748.
Leakage Inductance and Snubbers
Transformer leakage inductance (on either the primary
or secondary) causes a voltage spike to appear at the
primary after the MOSFET switch turns off. This spike is
increasingly prominent at higher load currents where more
stored energy must be dissipated. Transformer leakage
inductance should be minimized.
In most cases, proper selection of the external MOSFET
and a well designed transformer will eliminate the need for
snubber circuitry, but in some cases the optimal MOSFET
may require protection from this leakage spike. An RC
(resistor capacitor) snubber may be sufficient in applica-
tions where the MOSFET has significant margin beyond
the predicted DC drain voltage applied in flyback while a
clamp using an RCD (resistor capacitor diode) or a Zener
might be a better option when using a MOSFET with very
little margin for leakage inductance spiking.
The recommended approach for designing an RC snubber
is to measure the period of the ringing at the MOSFET drain
when the MOSFET turns off without the snubber and then
add capacitance—starting with something in the range of
100pF—until the period of the ringing is 1.5 to 2 times
longer. The change in period will determine the value of the
parasitic capacitance, from which the parasitic inductance
can be determined from the initial period, as well. Similarly,
initial values can be estimating using stated switch capaci-
tance and transformer leakage inductance. Once the value
of the drain node capacitance and inductance is known, a
series resistor can be added to the snubber capacitance
to dissipate power and critically dampen the ringing. The
equation for deriving the optimal series resistance using
the observed periods (tPERIOD, and tPERIOD(SNUBBED)) and
snubber capacitance (CSNUBBER)isbelow,andtheresultant
waveforms are shown in Figure 6.
CPAR =
CSNUBBER
tPERIOD(SNUBBED)
tPERIOD
2
–1
LPAR =
tPERIOD2
CPAR 4π
2
RSNUBBER =
LPAR
CPAR
TIME (μs)
0
V
DRAIN
(V)
10
30
40
50
0.20
90
3748 F06
20
0.10
0.05
0.25
0.15
0.30
60
70
80
NO SNUBBER
WITH SNUBBER
CAPACITOR
WITH RESISTOR
AND CAPACITOR
Figure 6. Observed Waveforms at MOSFET Drain when
Iteratively Implementing an RC Snubber
Note that energy absorbed by a snubber will be converted
to heat and will not be delivered to the load. In high volt-
age or high current applications, the snubber may need to
be sized for thermal dissipation. To determine the power
dissipated in the snubber resistor from capacitive losses,
measure the drain voltage immediately before the MOSFET
turns on and use the following equation relating that volt-
age and the MOSFET switching frequency to determine
the expected power dissipation:
PSNUBBER = fSW CSNUBBER VDRAIN2/2
Decreasing the value of the capacitor will reduce the dis-
sipated power in the snubber at the expense of increased
peak voltage on the MOSFET drain, while increasing the
value of the capacitance will decrease the overshoot.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3748HMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LT3748HMS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3748HMSPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748HMSTRPBF | 制造商:LINER 制造商全称: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 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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