A8430

更新时间： 2024-02-05 14:50:00

品牌	Logo	应用领域
急速微 - ALLEGRO		转换器驱动升压转换器
页数	文件大小	规格书
10页	328K
描述
White LED Driver Constant Current Step-up Converter

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技术参数
数据手册

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A8430 技术参数

生命周期：	Obsolete	Reach Compliance Code：	unknown
风险等级：	5.84	特性阻抗：	50 Ω
最大输入功率 (CW)：	43.98 dBm	最大工作频率：	4000 MHz
最小工作频率：		最高工作温度：	125 °C
最低工作温度：	-55 °C	射频/微波设备类型：	FIXED ATTENUATOR
最大电压驻波比：	1.35	Base Number Matches：	1

A8430 数据手册

A8430

White LED Driver Constant Current Step-up Converter

Device Operation

The A8430 uses a constant-frequency, current-mode control

scheme to regulate the current through the load. The load

current produces a voltage across the external sense resistor

(R1) and the input at the FB pin. This voltage is then

compared to the internal 95 mV reference to produce an error

signal. The switch current is sensed by the internal sense

resistor and compared to the load current error signal. As the

load current increases, the error signal diminishes, reducing

the maximum switch current and thus the current delivered

to the load. As the load current decreases, the error signal

rises, increasing the maximum switch current and thus

increasing the current delivered to the load.

The table below shows typical values for R1. Note that the

resistance value is from the standard E96 series.

As load current is reduced, the energy required in the

inductor diminishes, resulting in the inductor current

dropping to zero for low load current levels. This is known

as Discontinuous mode operation, and results in some low-

frequency ripple. The average load current, however, remains

regulated down to zero.

In Discontinuous mode, when the inductor current drops to

zero, the voltage at the SW pin rings, due to the capacitance

in the resonant LC circuit formed by the inductor and the

capacitance of the switch and the diode. This ringing is

low-frequency and is not harmful. It can be damped with a

resistor across the inductor, but this reduces efficiency and is

not recommended.

To set the load current, ensure that the required internal

reference value of 95 mV is produced at the desired load. To

do so, select a resistance value for the sense resistor, R1 (Ω),

such that:

R1=95 mV/I_LOAD

where I_LOADis the target load current (mA).

Power Dissipation versus I_OUT

120

110

100

Target Load Current

Sense Resistor (R1)

(I_LOAD

)

(Ω)

(mA)

19.1

9.53

7.87

6.34

4.75

I_OUT(mA)

Vin = 3V, 3 LED

Vin = 5V, 3 LED

Vin = 3V, 4 LED

Vin = 5V, 4 LED

www.allegromicro.com

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

1 2 3 456 7 8...10

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