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参数资料
| 型号： | LT3956EUHE#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PQCC36 |
| 封装： | 5 X 6 MM, LEAD FREE, PLASTIC, QFN-36 |
| 文件页数： | 4/20页 |
| 文件大小： | 1424K |
| 代理商： | LT3956EUHE#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
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3956IUHE#PBF | 功能描述:IC LED DVR BUCK BOOST 36-VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:6,000 系列:- 恒定电流:- 恒定电压:- 拓扑:开路漏极，PWM 输出数:4 内部驱动器:是 类型 - 主要:LED 闪烁器 类型 - 次要:- 频率:400kHz 电源电压:2.3 V ~ 5.5 V 输出电压:- 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘 供应商设备封装:8-HVSON 包装:带卷 (TR) 工作温度:-40°C ~ 85°C 其它名称:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
| LT3956IUHE#TRPBF | 功能描述:IC LED DVR BUCK BOOST 36-VQFN RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:6,000 系列:- 恒定电流:- 恒定电压:- 拓扑:开路漏极，PWM 输出数:4 内部驱动器:是 类型 - 主要:LED 闪烁器 类型 - 次要:- 频率:400kHz 电源电压:2.3 V ~ 5.5 V 输出电压:- 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘 供应商设备封装:8-HVSON 包装:带卷 (TR) 工作温度:-40°C ~ 85°C 其它名称:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
| LT3956IUHE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:80VIN, 80VOUT Constant-Current, Constant-Voltage Converter |
| LT3956IUHE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:80VIN, 80VOUT Constant-Current, Constant-Voltage Converter |
| LT3957 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Wide Input Voltage Range |
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