參數(shù)資料
型號(hào)： LT1737IS
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： High Power Isolated Flyback Controller
中文描述： SWITCHING CONTROLLER, 250 kHz SWITCHING FREQ-MAX, PDSO16
封裝： 0.150 INCH, PLASTIC, SO-16
文件頁(yè)數(shù)： 15/28頁(yè)
文件大?。?/td> 320K
代理商： LT1737IS
15
LT1737
1737f
implications regarding output voltage regulation at mini-
mum load (see Minimum Load Considerations).
A second benefit of the enable delay time function occurs
at light load. Under such conditions the amount of energy
stored in the transformer is small. The flyback waveform
becomes “l(fā)azy” and some time elapses before it indicates
the actual secondary output voltage (see Figure 4C). So
the enable delay time should also be set long enough to
ignore the “irrelevant” portion of the flyback waveform at
light load.
Additionally, there are cases wherein the gate output is
called upon to drive a large geometry MOSFET such that
the turnoff transition is slowed significantly. Under such
circumstances, the enable delay time may be increased to
accommodate for the lengthy transition.
Average “start-up” V
C
current =
MinimumEnableTime
SwitchingFrequency
I
SRC
Minimum enable time can also have implications at light
load (see Minimum Load Considerations). The temptation
is to set the minimum enable time to be fairly short, as this
is the least restrictive in terms of minimum load behavior.
However, to provide a “reliable” minimum start-up current
of say, nominally 1
μ
A, the user should set the minimum
enable time at no less that 2% of the switching period
(= 1/switching frequency).
CURRENT SENSE RESISTOR CONSIDERATIONS
The external current sense resistor allows the user to
optimize the current limit behavior for the particular appli-
cation under consideration. As the current sense resistor
is varied from several ohms down to tens of milliohms,
peak switch current goes from a fraction of an ampere to
tens of amperes. Care must be taken to ensure proper
circuit operation, especially with small current sense
resistor values.
For example, a peak switch current of 10A requires a
sense resistor of 0.025
. Note that the instantaneous
peak power in the sense resistor is 2.5W, and it must be
rated accordingly. The LT1737 has only a single sense line
to this resistor. Therefore, any parasitic resistance in the
ground side connection of the sense resistor will increase
its apparent value. In the case of a 0.025
sense resistor,
one milliohmof parasitic resistance will cause a 4%
reduction in peak switch current. So resistance of printed
circuit copper traces and vias cannot necessarily be
ignored.
An additional consideration is parasitic inductance. In-
ductance in series with the current sense resistor will
accentuate the high frequency components of the current
waveform. In particular, the gate switching spike and
multimegahertz ringing at the MOSFET can be
considerably amplified. If severe enough, this can cause
erratic operation. For example, assume 3nH of parasitic
inductance (equivalent to about 0.1 inch of wire in free
space) is in series with an ideal 0.025
sense resistor.
A “zero” will be formed at f = R/(2
π
L), or 1.3MHz. Above
APPLICATIOU
W
U
U
ENABLE DELAY
TIME NEEDED
1737 F04
DISCONTINUOUS
MODE
RINGING
IDEALIZED FLYBACK
WAVEFORM
MOSFET GATE DRIVE
FLYBACK WAVEFORM
WITH LARGE LEAKAGE
SPIKE AT HEAVY LOAD
“SLOW” FLYBACK
WAVEFORM AT
LIGHT LOAD
B
A
C
ENABLE
DELAY
TIME
NEEDED
Figure 4
Minimum Enable Time
This function sets a minimum duration for the expected
flyback pulse. Its primary purpose is to provide a mini-
mum source current at the V
C
node to avoid start-up
problems.
相關(guān)PDF資料
PDF描述
LT1737CGN High Power Isolated Flyback Controller
LT1737IGN High Power Isolated Flyback Controller
LT1737 High Power Switching Regulator for Isolated Flyback Controller(大功率，用于隔離回掃控制器的開(kāi)關(guān)穩(wěn)壓器)
LT1738 Slew Rate Controlled Ultralow Noise DC/DC Controller
LT1738EG Slew Rate Controlled Ultralow Noise DC/DC Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LT1737IS#PBF 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LT1737IS#PBF 制造商:Linear Technology 功能描述:ICSMPS CONTROLLERCURRENT-MOD 制造商:Linear Technology 功能描述:IC,SMPS CONTROLLER,CURRENT-MODE,SOP,16PI
LT1737IS#TR 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LT1737IS#TRPBF 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LT1738 制造商:LINER 制造商全稱:Linear Technology 功能描述:Slew Rate Controlled Ultralow Noise DC/DC Controller
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