参数资料
| 型号： | LT3587EUD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/24页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST INV ADJ DL 20QFN |
| 标准包装： | 2,500 |
| 类型： | 升压（升压），反相 |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 可调至 ±32V |
| 输入电压： | 2.5 V ~ 6 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1MHz |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 20-QFN 裸露焊盘（3x3） |
LT3587
APPLICATIONS INFORMATION
V VIN
2.5V TO 5V
10 μ H
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
V IN
LT3587
SW3
CAP3
V OUT3
1 μ F
LED DRIVER
20mA
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
I FB3
R IFB3
8.06k
EN/SS3
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
2.5V
0V
PWM
FREQ
MN1
Si1304BDL
3587 F13
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
Figure 13. Six White LEDs Driver With PWM Dimming
open-circuit voltage at the V OUT3 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
I VOUT3
13mA/DIV
I L4
200mA/DIV
ENSS3
5V/DIV
0mA
0mA
0V
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
I VOUT3 = 160V/R IFB3 ?ows through the LEDs. When the
PWM signal goes low, the LEDs are disconnected and
turned off.
V VIN = 3.6V
6 LEDs
2ms/DIV
3587 F14
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. PWM Dimming Waveforms
Figure 14 shows the PWM dimming waveforms for the
circuit in Figure 13.
3587fc
17
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