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LT3476
APPLICATIONS INFORMATION
V REF
througharesistordivider,orconnecteddirectlytoREFto
give the full-scale threshold of 105mV. A DAC may also be
used to drive the V ADJ pins. The V ADJ pins should not be
left open. If the V ADJ input is connected to a voltage higher
than 1.25V, the default regulation threshold across CAP
and LED is 125mV (typ). The V ADJ pin can also be used
in conjunction with a PTC thermistor to provide overtem-
perature protection for the LED load as shown in Figure 2.
Dimming Control
There are two methods to control the current source for
dimming using the LT3476. The first method, popular
with LED applications, uses the PWM pin to modulate the
1.05V
20k 25k
V ADJ 1-4
470
PTC
3476 F01
current source between zero and full current to achieve
a precisely programmed average current. To make this
method of current control more accurate, during the qui-
escent phase the switch demand current is stored on the
V C node. This feature minimizes recovery time when the
PWM signal goes high. The minimum PWM on- or off-time
will depend on the choice of operating frequency through
the RT input pin. For best current accuracy, the minimum
PWM low or high time should be at least ten switching
cycles. This guideline has two reasons: first to allow the
output to reach steady state before shutting off, and second
because the oscillator is not synchronized to the PWM
signal and there may be as much as one switching cycle
delay from PWM going high to the start of switching. This
delay, however, does not apply to the negative transition
of the PWM signal. The minimum PWM low/high time can
be reduced to five switching cycles if a disconnect switch
is used in the LED current path.
The second method of dimming control uses the V ADJ pin
to linearly adjust the current sense threshold during the
PWM high state. The LED current programming feature
augments the PWM dimming control, possibly increasing
total dimming range by a factor of ten.
Figure 2. Overtemperature Protect Circuit
3476fb
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相关代理商/技术参数
LT3476EUHF#TR
制造商:Linear Technology 功能描述:SP-SWREG/LED Driver, High Current Quad Output LED Driver in QFN (5x7)
LT3476EUHF#TRPBF
功能描述:IC LED DRVR HP CONST CURR 38-QFN 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
LT3476EUHF-PBF
制造商:LINER 制造商全称:Linear Technology 功能描述:High Current Quad Output LED Driver
LT3476EUHF-TR
制造商:LINER 制造商全称:Linear Technology 功能描述:High Current Quad Output LED Driver
LT3476EUHF-TRPBF
制造商:LINER 制造商全称:Linear Technology 功能描述:High Current Quad Output LED Driver
LT3476IUHF#PBF
功能描述:IC LED DRVR HP CONST CURR 38QFN 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
LT3476IUHF#TRPBF
功能描述:IC LED DRVR HP CONST CURR 38QFN 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
LT3477
制造商:LINER 制造商全称:Linear Technology 功能描述:Full-Featured LED Driver with 1.5A Switch Current