AL8821SP-13 Просмотр технического описания (PDF) - Diodes Incorporated.

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AL8821SP-13

40V, 2A BOOST LED DRIVER

Diodes Incorporated. 

AL8821

Application Information (Cont.)

VLT







(VCOMP



1.5) 0.6 1.4

16

mV ,1.5V

 VCOMP

 5V

88mV , 0V  VCOMP  1.5V

The range of VCOMP is from 0V to 5V.

The upper threshold depends on the lower threshold and the hysteresis value. The hysteresis value is set by external resister RHYS. It is defined as

below.

VHYS  RHYS 100 A

According to the operation principle , the peak to peak current ∆IL and the valley current IL(val) can be obtained by the below equations.

I L(val)



VLT

RSET

I L



VHYS

RSET

Where:

∆IL is the peak to peak current of inductor.

IL(val) is the valley current of inductor.

From the Figure 2, the relationship between IL(peak), IL(val), IL(ave) and ∆IL can be obtained as below.

I L( peak)  I L(val)  I L

I L(ave)



I L(val)



1

2

 IL

Where:

IL(peak) is the peak current of inductor.

IL(ave) is the average current of inductor.

As we know the average current IL(ave) depends on the output power, rated input voltage VIN1 of step-up converter and total efficiency η. So the

average current IL(ave) can be obtained by the following equation.

I L(ave)



(VLED

 0.444 )  I LED

 VIN1

Where: VLED is the voltage in LEDs.

Set ratio of ∆IL to IL(peak) as K.

AL8821

Document number: DS37671 Rev. 1 - 2

8 of 14

www.diodes.com

January 2015

© Diodes Incorporated

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