AL8862Q
Application Information (continued)
1200
1000
800
600
400
200
0
RSET=0.1
RSET=0.15
RSET=0.3
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
CTRL Pin Voltage (V)
Figure 1. Analog Dimming Curve
Soft-Start
The default soft-start time for the AL8862Q is 0.1ms – this provides very fast turn-on of the output, improving the PWM dimming accuracy.
Nevertheless, adding an external capacitor from the CTRL pin to ground will provide a longer soft-start delay. This is achieved by increasing the
time for the CTRL voltage rising to the turn-on threshold and by slowing down the rising rate of the control voltage at the input of hysteresis
comparator. The additional soft-start time is related to the capacitance between CTRL pin and GND, the typical value will be 1.5ms/nF.
Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and
will reduce the overall efficiency. This capacitor can supply the relatively high peak current to the coil and smooth the ripple on the input current.
The minimum capacitance needed is determined by input power, cable’s length and peak current. 4.7μF to 10μF is a common used value range
for most of cases. A higher value will improve performance at lower input voltages, especially when the source impedance is high. The input
capacitor should be placed as close as possible to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with Y5V
dielectric are not suitable for decoupling in this application and should NOT be used.
Freewheel Diode Selection
For maximum efficiency and performance, the freewheeling diode (D1) should be a fast low capacitance Schottky diode with low reverse leakage
current. It also provides better efficiency than silicon diodes, due to the lower forward voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum
output load current. It is very important to control the reverse leakage current of the diode when operating above +85°C. Excess leakage current
will increase power dissipation.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak output voltage on the SW pins. If a
silicon diode is used, more care should be taken to ensure that the total voltage appearing on the SW pins including supply ripple, will not exceed
the specified maximum value.
10 of 17
www.diodes.com
July 2023
AL8862Q
© 2023 Copyright Diodes Incorporated. All Rights Reserved.
Document number: DS42199 Rev. 5 - 2
5秒后页面跳转
深入解析CS8416引脚说明、参数、技术特点
TPA3116D2功放芯片参数详解、引脚说明
移位寄存器74HC165引脚说明、驱动程序示例解读
深入解析AD9833：DDS频率合成器的卓越性能与广泛应用
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
数据手册
如果您发现信息不准确，
