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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： | 30/30页 |
| 文件大小： | 284K |
| 代理商： | LT3748EMS#TRPBF |
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LT3748
9
3748fa
Pseudo-DC Theory of Operation
The RREFandRFBresistorsasdepictedintheBlockDiagram
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 VIN. The amplitude
of this flyback pulse (i.e., the difference between it and
VIN) is given as:
VFLBK = (VOUT + VF + ISEC ESR) NPS
VF = DOUT forward voltage
ISEC = Transformer secondary current
ESR = Total impedance of secondary circuit
NPS = Transformer effective primary-to-secondary
turns ratio
The flyback voltage is converted to a current by RFB and
Q2. Nearly all of this current flows through resistor RREF 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.
The relatively high gain in the overall loop will then cause
the voltage at the RREF resistor to be nearly equal to the
bandgap reference voltage, VBG. The relationship between
VFLBK and VBG may then be expressed as:
VFLBK
RFB
=
VBG
RREF
or
VFLBK = VBG
RFB
RREF
VBG = Internal bandgap reference
Combining with the previous VFLBK expression yields an
expression for VOUT, in terms of the internal reference,
programming resistors, transformer turns ratio and diode
forward voltage drop:
VOUT = VBG
RFB
RREF
1
NPS
VF ISEC (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 VOUT equation does not have a tem-
perature dependence, but the diode forward drop, VF, has a
significant negative temperature coefficient. To compensate
for this, a positive temperature coefficient current source
is internally connected to the RREF pin. The current is set
by resistor RTC to ground connected between the TC pin
and ground. To cancel the temperature coefficient, the
following equation is used:
δVF
δT
=
RFB
RTC
1
NPS
δVTC
δT
or,
RTC =
RFB
NPS
1
δVF / δT
δVTC
δT
≈
RFB
NPS
(δVF/δT) = Diode’s forward voltage temperature coef-
ficient
(δVTC/δT) = 1.85mV/°C
VTC = 0.55V
The resistor value given by this equation should also
be verified experimentally and adjusted, if necessary, to
achieve optimal regulation over temperature.
The revised output voltage is as follows:
VOUT = VBG
RFB
RREF
1
NPS
VF
VTC
RTC
RFB
NPS
–ISEC (ESR)
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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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