Datasheet 搜索 > 稳压芯片 > Linear Technology（凌力尔特） > LTC3803HS6#TRPBF 数据手册 > LTC3803HS6#TRPBF 数据手册 7/16 页
￥ 18.668
LTC3803HS6#TRPBF 数据手册 - Linear Technology（凌力尔特）
制造商:
Linear Technology（凌力尔特）
分类:
稳压芯片
封装:
TSOT-23-6
Pictures:
3D模型
符号图
焊盘图
引脚图
产品图
页面导航:
引脚图在P6Hot
典型应用电路图在P1P12P13P16
原理图在P6P7
封装尺寸在P14
焊盘布局在P14
技术参数、封装参数在P4
应用领域在P1P4P8P9P10P11P12P13P16
电气规格在P3P4P5
导航目录
LTC3803HS6#TRPBF数据手册
Page:
of 16 Go
若手册格式错乱，请下载阅览PDF原文件
LTC3803
7
3803fc
OPERATION
The LTC3803 is a constant frequency current mode control-
ler for fl yback and DC/DC boost converter applications in
a tiny ThinSOT package. The LTC3803 is designed so that
none of its pins need to come in contact with the input or
output voltages of the power supply circuit of which it is
a part, allowing the conversion of voltages well beyond
the LTC3803’s absolute maximum ratings.
Main Control Loop
Due to space limitations, the basics of current mode
DC/DC conversion will not be discussed here; instead, the
reader is referred to the detailed treatment in Application
Note 19, or in texts such as Abraham Pressman’s
Switch-
ing Power Supply Design
.
Please refer to the Block Diagram and the Typical Ap-
plication on the front page of this data sheet. An external
resistive voltage divider presents a fraction of the output
voltage to the V
FB
pin. The divider must be designed so
that when the output is at the desired voltage, the V
FB
pin
voltage will equal the 800mV from the internal reference.
If the load current increases, the output voltage will de-
crease slightly, causing the V
FB
pin voltage to fall below
800mV. The error amplifi er responds by feeding current
into the I
TH
/RUN pin. If the load current decreases, the
V
FB
voltage will rise above 800mV and the error amplifi er
will sink current away from the I
TH
/RUN pin.
The voltage at the I
TH
/RUN pin commands the pulse-width
modulator formed by the oscillator, current comparator
and RS latch. Specifi cally, the voltage at the I
TH
/RUN pin
sets the current comparator’s trip threshold. The current
comparator monitors the voltage across a current sense
resistor in series with the source terminal of the external
MOSFET. The LTC3803 turns on the external power MOSFET
when the internal free-running 200kHz oscillator sets
the RS latch. It turns off the MOSFET when the current
comparator resets the latch or when 80% duty cycle is
reached, whichever happens fi rst. In this way, the peak
current levels through the fl yback transformer’s primary
and secondary are controlled by the I
TH
/RUN voltage.
Since the I
TH
/RUN voltage is increased by the error ampli-
fi er whenever the output voltage is below nominal, and
decreased whenever output voltage exceeds nominal, the
voltage regulation loop is closed. For example, whenever
the load current increases, output voltage will decrease
slightly, and sensing this, the error amplifi er raises the
I
TH
/RUN voltage by sourcing current into the I
TH
/RUN pin,
raising the current comparator threshold, thus increasing
the peak currents through the transformer primary and
secondary. This delivers more current to the load, bringing
the output voltage back up.
The I
TH
/RUN pin serves as the compensation point for
the control loop. Typically, an external series RC network
is connected from I
TH
/RUN to ground and is chosen for
optimal response to load and line transients. The impedance
of this RC network converts the output
current
of the error
amplifi er to the I
TH
/RUN
voltage
which sets the current
comparator threshold and commands considerable infl u-
ence over the dynamics of the voltage regulation loop.
Start-Up/Shutdown
The LTC3803 has two shutdown mechanisms to disable
and enable operation: an undervoltage lockout on the
V
CC
supply pin voltage, and a forced shutdown whenever
external circuitry drives the I
TH
/RUN pin low. The LTC3803
transitions into and out of shutdown according to the state
diagram (Figure 1).
Figure 1. Start-Up/Shutdown State Diagram
LTC3803
SHUT DOWN
V
ITH/RUN
< V
ITHSHDN
(NOMINALLY 0.28V)
3803 F01
V
CC
< V
TURNOFF
(NOMINALLY 5.7V)
V
ITH/RUN
> V
ITHSHDN
AND V
CC
> V
TURNON
(NOMINALLY 8.7V)
LTC3803
ENABLED
器件 Datasheet 文档搜索
AiEMA 数据库涵盖高达 72,405,303 个元件的数据手册，每天更新 5,000 多个 PDF 文件
