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参数资料
| 型号： | LT3748HMS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/30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 |
| 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 ~ 150°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 BG ?? FB ?? ?
R REF ? ? ? N PS ? ?
Pseudo-DC Theory of Operation
The R REF and R FB resistors as depicted in the Block Diagram
are external resistors used to program the output voltage.
The LT3748 operates much the same way as traditional
current mode switchers with the exception of the unique
error amplifier which derives its feedback information
from the flyback pulse.
Operation is as follows: when the NMOS output switch
turns off, its drain voltage rises above V IN . The amplitude
of this flyback pulse (i.e., the difference between it and
V IN ) is given as:
V FLBK = (V OUT + V F + I SEC ? ESR) ? N PS
V F = D OUT forward voltage
I SEC = Transformer secondary current
ESR = Total impedance of secondary circuit
N PS = Transformer effective primary-to-secondary
turns ratio
The flyback voltage is converted to a current by R FB and
Combining with the previous V FLBK expression yields an
expression for V OUT , in terms of the internal reference,
programming resistors, transformer turns ratio and diode
forward voltage drop:
? R ? ? 1 ?
? ? V F ? I SEC (ESR)
?
Additionally, it includes the effect of nonzero secondary
output impedance (ESR). This term can be assumed to
be zero in boundary control mode.
Temperature Compensation
The first term in the V OUT equation does not have a tem-
perature dependence, but the diode forward drop, V F , has a
significant negative temperature coefficient. To compensate
for this, a positive temperature coefficient current source
is internally connected to the R REF pin. The current is set
by resistor R TC to ground connected between the TC pin
and ground. To cancel the temperature coefficient, the
following equation is used:
R TC =
δ V TC
Q2.NearlyallofthiscurrentflowsthroughresistorR REF to
form a ground-referred voltage. This voltage is fed into the
flyback error amplifier. The flyback error amplifier samples
this output voltage information when the secondary-side
winding current reaches zero. The error amplifier uses a
bandgap voltage, 1.223V, as the reference voltage.
δ V F R FB
δ T R TC
= ?
? R FB
N PS
?
1
? ?
N PS
1
δ V F / δ T
δ V TC
δ T
?
δ T
or,
R FB
≈
N PS
The relatively high gain in the overall loop will then cause
the voltage at the R REF resistor to be nearly equal to the
bandgap reference voltage, V BG . The relationship between
V FLBK and V BG may then be expressed as:
( δ V F / δ T ) = Diode’s forward voltage temperature coef-
ficient
( δ V TC / δ T ) = 1.85mV/°C
? V FLBK ? V BG
? R ? R
? FB ?
? ?=
REF
or
V TC = 0.55V
The resistor value given by this equation should also
be verified experimentally and adjusted, if necessary, to
? R
V FLBK = V BG ?? FB ??
? R
? FB ? ? 1 ? ? V F
= V BG ?
V OUT
? R REF ? ? N PS ?
? ? FB – I SEC (ESR)
R TC ? ? N PS
?
? R REF ?
V BG = Internal bandgap reference
achieve optimal regulation over temperature.
The revised output voltage is as follows:
? ? ?
? ? ?
? V TC ? R
? ??
?
3748fa
9
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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) |
| LT3748IMS#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: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) |
| LT3748IMSPBF | 制造商:Linear Technology 功能描述:100V Isolated Flyback Controller MSOP16 |
| LT3748IMSTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:100V Isolated Flyback Controller |
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