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參數(shù)資料
| 型號： | LT3837IFE#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 110 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.40 MM, LEAD FREE, PLASTIC, TSSOP-16 |
| 文件頁數(shù)： | 13/28頁 |
| 文件大?。?/td> | 247K |
| 代理商： | LT3837IFE#PBF |
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LT3837
20
3837fc
APPLICATIONS INFORMATION
Minimum Load Considerations
At light loads, the LT3837 derived regulator goes into
forced continuous conduction mode. The primary side
switch always turns on for a short time as set by the
tON(MIN) resistor. If this produces more power than the
load requires, power will ow back into the primary during
the “off” period when the synchronization switch is on.
This does not produce any inherently adverse problems,
though light load efciency is reduced.
Maximum Load Considerations
The current mode control uses the VC node voltage and
amplied sense resistor voltage as inputs to the current
comparator. When the amplied sense voltage exceeds the
VC node voltage, the primary side switch is turned off.
In normal use, the peak switch current increases while
FB is below the internal reference. This continues until
VC reaches its 2.56V clamp. At clamp, the primary side
MOSFET will turn off at the rated 98mV VSENSE level. This
repeats on the next cycle.
It is possible for the peak primary switch currents as
referred across RSENSE to exceed the max 98mV rating
because of the minimum switch-on time blanking. If the
voltage on VSENSE reaches 206mV after the minimum
turn-on time, the SFST capacitor is discharged, which also
discharges the VC capacitor. This then reduces the peak
current on the next cycle and will reduce overall stress in
the primary switch.
Short-Circuit Conditions
Loss of current limit is possible under certain conditions
such as an output short-circuit. If the duty cycle exhib-
ited by the minimum on-time is greater than the ratio of
secondary winding voltage (referred-to-primary) divided
by input voltage, then peak current is not controlled at
the nominal value. It ratchets up cycle-by-cycle to some
higher level. Expressed mathematically, the requirement
to maintain short-circuit control is:
DC
t
f
IR
R
VN
MIN
ON MIN
OSC
SC
SEC
DS ON
IN
=<
+
()
SSP
where:
tON(MIN) = primary side switch minimum on-time
ISC = short-circuit output current
Other variables as previously dened.
Trouble is typically encountered only in applications with a
relatively high product of input voltage times secondary-
to-primary turns ratio and/or a relatively long minimum
switch-on time. Additionally, several real world effects such
as transformer leakage inductance, AC winding losses, and
output switch voltage drop combine to make this simple
theoretical calculation a conservative estimate. Prudent
design evaluates the switcher for short-circuit protection
and adds any additional circuitry to prevent destruction.
Output Voltage Error Sources
The LT3837’s feedback sensing introduces additional
sources of errors. The following is a summary list.
The internal bandgap voltage reference sets the reference
voltage for the feedback amplier. The specications detail
its variation.
The external feedback resistive divider ratio proportional
directly affects regulated voltage. Use 1% components.
Leakage inductance on the transformer secondary reduces
the effective secondary-to-feedback winding turns ratio
(NS/NF) from its ideal value. This increases the output volt-
age target by a similar percentage. Since secondary leakage
inductance is constant from part to part (with a tolerance)
adjust the feedback resistor ratio to compensate.
The transformer secondary current ows through the im-
pedances of the winding resistance, synchronous MOSFET
RDS(ON) and output capacitor ESR. The DC equivalent
current for these errors is higher than the load current
because conduction occurs only during the converter’s
“off” time. So divide the load current by (1 – DC).
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相關(guān)代理商/技術(shù)參數(shù) |
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| LT3844EFE#PBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| LT3844EFE#TRPBF | 功能描述:IC REG CTRLR BST INV PWM 16TSSOP 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 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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