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參數(shù)資料
| 型號： | LT3587EUD#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING REGULATOR, 1200 kHz SWITCHING FREQ-MAX, PQCC20 |
| 封裝： | 3 X 3 MM, LEAD FREE, PLASTIC, QFN-20 |
| 文件頁數(shù)： | 9/24頁 |
| 文件大小： | 395K |
| 代理商： | LT3587EUD#PBF |
LT3587
17
3587fc
APPLICATIONS INFORMATION
Figure 14. PWM Dimming Waveforms
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
typical human eye has a sensitivity limit of ~60Hz. By
increasing the PWM frequency to ~80Hz or higher, the eye
will interpret that the pulsed light source is continuously
on. Additionally, by modulating the duty cycle (amount of
“on-time”), intensity of the LEDs is controlled. The color
of the LEDs remains unchanged in this scheme since the
LED current is either zero or a constant value.
Figure 13 shows a partial application showing an LED
driver for six white LEDs. If the voltage at the CAP3 pin is
higher than 10V when the LEDs are on, direct PWM dim-
ming method requires an external NMOS. This external
NMOS is tied between the cathode of the lowest LED in
the string and ground as shown in Figure 13.
A Si1304 logic-level MOSFET can be used since its source
is connected to ground, and it is able to withstand the
open-circuit voltage at the VOUT3 pin across its drain and
source. The PWM signal must be applied to the EN/SS3
pin of the LT3587 and the gate of the NMOS. The PWM
signal should traverse between 0V to 2.5V, to ensure
proper turn on and off of the Boost3 regulation loop and
the NMOS transistor MN1. When the PWM signal goes
high, the LEDs are connected to ground and a current of
IVOUT3 = 160V/RIFB3 ows through the LEDs. When the
PWM signal goes low, the LEDs are disconnected and
turned off.
The output disconnect feature and the external NMOS
ensure that the LEDs quickly turn off without discharging
the output capacitor. This allows the LEDs to turn on faster.
Figure 14 shows the PWM dimming waveforms for the
circuit in Figure 13.
Figure 13. Six White LEDs Driver With PWM Dimming
10μH
3587 F13
VOUT3
CAP3
IFB3
LT3587
RIFB3
8.06k
EN/SS3
SW3
VIN
LED DRIVER
20mA
1μF
VVIN
2.5V TO 5V
PWM
FREQ
2.5V
0V
MN1
Si1304BDL
3587 F14
ENSS3
5V/DIV
IL4
200mA/DIV
IVOUT3
13mA/DIV
2ms/DIV
VVIN = 3.6V
6 LEDs
0mA
0V
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| LT3590EDC#TRPBF | 功能描述:IC LED DRIVER WHITE BCKLGT 6-DFN RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅動器 系列:- 標準包裝:6,000 系列:- 恒定電流:- 恒定電壓:- 拓撲:開路漏極，PWM 輸出數(shù):4 內部驅動器:是 類型 - 主要:LED 閃爍器 類型 - 次要:- 頻率:400kHz 電源電壓:2.3 V ~ 5.5 V 輸出電壓:- 安裝類型:表面貼裝 封裝/外殼:8-VFDFN 裸露焊盤 供應商設備封裝:8-HVSON 包裝:帶卷 (TR) 工作溫度:-40°C ~ 85°C 其它名稱:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
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