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| 型号： | LT3748EMS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 11/30页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO CM 16MSOP |
| 产品培训模块： | LT3748 100V Flyback Controller |
| 特色产品： | LT3748 Isolated Flyback Controller |
| 标准包装： | 37 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 电源电压： | 5 V ~ 100 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm），12 引线 |
| 包装： | 管件 |
| 配用： | 732-3308-ND - BOARD EVAL FOR LT3748 732-3305-ND - BOARD EVAL FOR LT3748 |
| 相关产品： | 732-2669-2-ND - TRANS FLYBACK LT3748 20UH SMD 732-2669-6-ND - TRANS FLYBACK LT3748 20UH SMD 732-2668-6-ND - TRANS FLYBACK LT3748 14UH SMD 732-2667-6-ND - TRANS FLYBACK LT3748 500UH SMD 732-2666-6-ND - TRANS FLYBACK LT3748 12UH SMD 732-2665-6-ND - TRANS FLYBACK LT3748 12UH SMD 732-2664-6-ND - TRANS FLYBACK LT3748 15UH SMD 732-2663-6-ND - TRANS FLYBACK LT3748 15UH SMD 732-2662-6-ND - TRANS FLYBACK LT3748 8UH SMD 732-2661-6-ND - TRANS FLYBACK LT3748 8UH SMD 更多... |
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LT3748
APPLICATIONS INFORMATION
( V OUT + V F(DIODE) ) ? R SENSE ? t SETTLE(MIN) ? N PS
Minimum Primary Inductance Requirements
The LT3748 obtains output voltage information from the
external MOSFET drain voltage when the secondary winding
conducts current. The sampling circuitry needs a minimum
of 400ns to settle and sample the output voltage while the
MOSFET switch is off. This required settle and sample
time is controlled by external components independent of
the minimum off-time of the GATE pin as specified in the
Electrical Characteristics table. The electrical specification
minimum off-time is based on an internal timer and acts
as a maximum frequency clamp. The following equation
gives the minimum value for primary-side magnetizing
inductance:
L PRI ≥
V SENSE(MIN)
V SENSE(MIN) = 15mV
t SETTLE(MIN) = 400ns
N PS = Ratio of primary windings to secondary windings
In addition to the primary inductance requirement for
minimum settling and sampling time, the LT3748 has
internal circuit constraints that prevent it from setting the
GATE node high for shorter than approximately 250ns.
If the inductor current exceeds the desired current limit
during that time oscillation may occur at the output as
the current control loop will lose its ability to regulate.
Therefore, the following equation relating to maximum
input voltage must also be followed in selecting primary-
side magnetizing inductance:
Output Power
Because the MOSFET power switch is located outside the
LT3748, the maximum output power is primarily limited
by external components. Output power limitations can
be separated into three categories—voltage limitations,
current limitations and thermal limitations.
The voltage limitations in a flyback design are primarily
the MOSFET switch V DS(MAX) and the output diode re-
verse-bias rating. Increasing the voltage rating of either
component will typically decrease application efficiency if
all else is equal and the voltage requirements on each of
those components will be directly related to the windings
ratio of the transformer, the input and output voltages
and the use of any additional snubbing components.
The MOSFET V DS(MAX) must theoretically be higher than
V IN(MAX) + (V OUT ? N PS ) and the output diode reverse bias
must be higher than V OUT + (V IN(MAX) /N PS ), though leak-
age inductance spikes on both the drain of the MOSFET
and the anode of the output diode may more than double
that requirement (see section on leakage inductance for
more details on snubbers). Figure 1 illustrates the effect
on available output power for several MOSFET voltage
ratings while continuously maximizing windings ratio
for input voltage with a fixed MOSFET current limit and
output voltage. Increasing the MOSFET rating increases
the possible windings ratio and or maximum input voltage
and can increase the available output power for a given
application. Both figures assume no leakage inductance
and high efficiency.
L PRI ≥
V IN(MAX) ? R SENSE ? t ON(MIN)
V SENSE(MIN)
50
40
V DS = 200V
V DS = 150V
t ON(MIN) = 250ns
The last constraint on minimum inductance value would
relate to minimum full-load operating frequency, f MIN , and
is derived from f SW = 1/(t ON + t OFF ):
L PRI ≤ V IN(MIN) ? (V OUT + V F(DIODE) ) ? N PS /(f SW(MIN) ? I LIM ?
30
20
10
V DS = 100V
((V OUT + V F(DIODE) ) ? N PS + V IN(MIN) ))
0
0
20
40
60
80
100
The minimum operating frequency may be lower than
the calculated number due to delays in detecting current
INPUT VOLTAGE (V)
3748 F01
limit and detecting boundary mode that are specific to
each application.
Figure 1. Maximum Output Power at 12V OUT with a
3A I LIM and Maximum V DS = 100V, 150V, 200V
3748fa
11
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3748EMSTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:100V Isolated Flyback Controller |
| 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 |
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