參數(shù)資料
型號(hào)： LT3956IUHE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, PQCC36
封裝： 5 X 6 MM, LEAD FREE, PLASTIC, QFN-36
文件頁(yè)數(shù)： 4/20頁(yè)
文件大?。?/td> 1424K
代理商： LT3956IUHE#TRPBF
LT3956
3956f
applicaTions inForMaTion
Dimming Control
There are two methods to control the current source for
dimming using the LT3956. One method uses the CTRL
pin to adjust the current regulated in the LEDs. A second
method uses the PWM pin to modulate the current source
between zero and full current to achieve a precisely pro-
grammed average current. To make this method of current
controlmoreaccurate,theswitchdemandcurrentisstored
on the VC node during the quiescent phase when PWM is
low. This feature minimizes recovery time when the PWM
signal goes high. To further improve the recovery time, a
disconnect switch may be used in the LED current path to
prevent the ISP node from discharging during the PWM
signal low phase. The minimum PWM on or off time will
depend on the choice of operating frequency through the
RTinput.Forbestoverallperformance,theminimumPWM
low or high time should be at least six switching cycles
(6μs for fSW = 1MHz).
Programming the Switching Frequency
The RT frequency adjust pin allows the user to program
the switching frequency from 100kHz to 1MHz to optimize
efficiency/performanceorexternalcomponentsize.Higher
frequency operation yields smaller component size but
increases switching losses and gate driving current, and
may not allow sufficiently high or low duty cycle operation.
Lowerfrequencyoperationgivesbetterperformanceatthe
cost of larger external component size. For an appropriate
RT resistor value see Table 1. An external resistor from the
RT pin to GND is required—do not leave this pin open.
Table 1. Switching Frequency vs RT Value
fOSC (kHz)
RT (k)
1000
10
900
11.8
800
13
700
15.4
600
17.8
500
21
400
26.7
300
35.7
200
53.6
100
Duty Cycle Considerations
Switching duty cycle is a key variable defining converter
operation, therefore, its limits must be considered when
programming the switching frequency for a particular
application. The fixed minimum on-time and minimum
off-time (see Figure 4) and the switching frequency define
the minimum and maximum duty cycle of the switch,
respectively. The following equations express the mini-
mum/maximum duty cycle:
Min Duty Cycle = (minimum on-time) switching
frequency
Max Duty Cycle = 1 – (minimum off-time) switching
frequency
When calculating the operating limits, the typical values
for on/off-time in the data sheet should be increased by at
least 60ns to allow margin for PWM control latitude and
SW node rise/fall times.
0
100
200
300
50
150
250
3956 F04
TIME
(ns)
TEMPERATURE (°C)
–50
0
50
75
–25
25
100 125
MINIMUM ON-TIME
MINIMUM OFF-TIME
Figure 4. Typical Switch Minimum On
and Off Pulse Width vs Temperature
Thermal Considerations
The LT3956 is rated to a maximum input voltage of 80V.
Careful attention must be paid to the internal power dis-
sipation of the IC at higher input voltages to ensure that a
junctiontemperatureof125°Cisnotexceeded.Thisjunction
limitisespeciallyimportantwhenoperatingathighambient
temperatures.IftheLT3956’sjunctiontemperaturereaches
165°C (typ), the power switch will be turned off and the
soft-start (SS) pin will be discharged to GND. Switching
相關(guān)PDF資料
PDF描述
LT3957EUHE#TRPBF SWITCHING REGULATOR, PQCC36
LT3957IUHE#PBF SWITCHING REGULATOR, PQCC36
LT3958IUHE#PBF SWITCHING REGULATOR, PQCC36
LT3958EUHE#PBF SWITCHING REGULATOR, PQCC36
LT3958EUHE#TRPBF SWITCHING REGULATOR, PQCC36
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LT3957 制造商:LINER 制造商全稱:Linear Technology 功能描述:Wide Input Voltage Range
LT3957A 制造商:LINER 制造商全稱:Linear Technology 功能描述:Boost, Flyback, SEPIC and Inverting Converter
LT3957AEUHE#PBF 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁(yè)面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2
LT3957AEUHE#TRPBF 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V，1.5V，1.8V，2.5V 輸入電壓:2.7 V ~ 20 V PWM 型:- 頻率 - 開關(guān):- 電流 - 輸出:50mA 同步整流器:是 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬）裸露焊盤 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:10-MSOP 裸露焊盤
LT3957AIUHE#PBF 功能描述:IC REG MULTI CONFIG ADJ 5A 36QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)包裝:250 系列:- 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:1.2V 輸入電壓:2.05 V ~ 6 V PWM 型:電壓模式 頻率 - 開關(guān):2MHz 電流 - 輸出:500mA 同步整流器:是 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:6-UFDFN 包裝:帶卷 (TR) 供應(yīng)商設(shè)備封裝:6-SON（1.45x1） 產(chǎn)品目錄頁(yè)面:1032 (CN2011-ZH PDF) 其它名稱:296-25628-2
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