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| 型号： | LT3478EFE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 15/24页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 16TSSOP |
| 标准包装： | 95 |
| 恒定电流： | 是 |
| 拓扑： | PWM，降压（降压），升压（升压） |
| 输出数： | 1 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 车载，背光 |
| 类型 - 次要： | 颜色，白色 LED |
| 频率： | 200kHz ~ 2.25MHz |
| 电源电压： | 2.8 V ~ 36 V |
| 输出电压： | 42V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 16-TSSOP-EP |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 125°C |
LT3478/LT3478-1
APPLICATIO S I FOR ATIO
The value for R4 can now be solved using equation (a)
where,
R4 = 0.77 (R NTC (25°C) + R Y ) = 0.77 (22k + 7.5k)
R4 = 22.7k (choose 22.6k)
for the output LED(s) is programmed for a given bright-
ness/color and “chopped” over a PWM duty cycle range
(Figure 10) from 100% to as low as 0.033%.
D2
I LED slope can now be calculated from,
I LED slope = [CTRL2(50°C) – CTRL2(25°C)]/25°C
where CTRL2 (50°C) = 1.24/(1 + 22.6/(7.9 + 7.5)) =
503mV
V IN
SHDN
V REF
CTRL2
V S
L
LT3478/
LT3478-1
SW
V OUT
C OUT
(LT3478)
R SENSE
and CTRL2 (25°C) = 1.24/(1 + 39.2/(22 + 28.7)) =
CTRL1
699mV
OVPSET
LED
giving I LED slope (from 25°C to 50°C)
R T
V C
PWM
D1
= 503mV – 699mV/25°C
PWM DIMMING
= –196mV/25°C => I LED slope = –196mA/25°C
CONTROL
3478 F09
Using the Murata simulation tool for the resistor network
and values in the above example shows a CTRL2 volt-
Figure 9. PWM Dimming Control Using the LT3478/LT3478-1
age curve that ?attens out as temperatures approach
100°C ambient. The ?nal resistor network chosen for the
derating curve in Figure 6 used option C network with
PWM
T PWM
TON PWM
(= 1/f PWM )
R4 = 19.3k, R NTC = 22k (NCP15XW223J0SRC) and R Y
= 3.01k. Although the CTRL2 downward slope is greater
than –200mA/25°C initially, the slope is required to avoid
exceeding maximum allowed LED currents at high ambient
INDUCTOR
CURRENT
temperatures (see Figure 6).
LED
CURRENT
MAX I LED
PWM Dimming
Many LED applications require an accurate control of the
brightness of the LED(s). In addition, being able to main-
Figure 10. PWM Dimming Waveforms Using the
LT3478/LT3478-1
3478 F10
tain a constant color over the entire dimming range can
be just as critical. For constant color LED dimming, the
LT3478/LT3478-1 provide a PWM pin and special internal
circuitry to allow up to a 3000:1 wide PWM dimming
range. With an N-channel MOSFET connected between
the LED(s) and ground and a PWM signal connected to
the gate of the MOSFET and the PWM pin (Figure 9), it
is possible to control the brightness of the LED(s) based
on PWM signal duty cycle only. This form of dimming is
superior to dimming control using an analog input voltage
(reducing CTRL1 voltage) because it allows constant color
to be maintained during dimming. The maximum current
Some general guidelines for LED Current Dimming using
the PWM pin (see Figure 10):
(1) PWM Dimming Ratio (PDR) = 1/(PWM duty cycle) =
1/(TON PWM ? f PWM )
(2) Lower f PWM allows higher PWM Dimming Ratios
(use minimum f PWM = 100Hz to avoid visible ?icker and
to maximize PDR)
(3) Higher f OSC value improves PDR (allows lower TON PWM )
but will reduce ef?ciency and increase internal heating. In
general, minimum operational TON PWM = 3 ? (1/f OSC ).
(4) Lower inductor value improves PDR
34781f
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3478IFE | 制造商:LINER 制造商全称:Linear Technology 功能描述:4.5A Monolithic LED Drivers with True Color PWM Dimming |
| LT3478IFE#PBF | 功能描述:IC LED DRVR HP CONS CURR 16TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:60 系列:- 恒定电流:- 恒定电压:- 拓扑:线性（LDO），PWM，升压（升压） 输出数:8 内部驱动器:是 类型 - 主要:背光 类型 - 次要:RGB，白色 LED 频率:500kHz ~ 1.5MHz 电源电压:4.75 V ~ 26 V 输出电压:45V 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* 工作温度:-40°C ~ 85°C |
| LT3478IFE#TRPBF | 功能描述:IC LED DRVR HP CONS CURR 16TSSOP 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 |
| LT3478IFE-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:4.5A Monolithic LED Drivers with True Color PWM Dimming |
| LT3478IFE-1#PBF | 功能描述:IC LED DRVR HP CONS CURR 16TSSOP 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 |
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