Datasheet > A8515

A8515

更新时间： 2024-02-10 14:16:10

品牌	Logo	应用领域
急速微 - ALLEGRO		驱动器显示器
页数	文件大小	规格书
34页	1183K
描述
The A8515 is a multi-output white LED (WLED) driver for LCD backlighting in consumer and industrial displays.

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A8515 数据手册

Wide Input Voltage Range, High Efficiency

Fault Tolerant LED Driver

A8515

The reverse breakdown voltage rating for the output diode in a

SEPIC circuit should be:

A capacitor larger than 3.96 μF should be selected due to degra-

dation of capacitance at high voltages on the capacitor. Select a

4.7 μF capacitor for this application.

V_BD> V_OUT(OVP)(max) + V_IN(max)

(44)

> 15.9 (V) + 16 (V) = 31.9 V

because the maximum output voltage in this case is V_OUT(OVP)

The rms current through the capacitor is given by:

(47)

The peak current through the diode is calculated as:

D(max)

I_COUTrms

OUT

I_dp= I_IN(max) + ¹/₂ΔI_Lused

(45)

1 – D(max)

= 0.848 (A) + 0.096 (A) = 0.944 A

0.765

1 – 0.765

0.240 (A)

0.433 A

The third major component in deciding the switching diode is the

reverse current, I_R, characteristic of the diode. This characteristic

is especially important when PWM dimming is implemented.

During PWM off-time the boost converter is not switching. This

results in a slow bleeding off of the output voltage, due to leakage

currents. I_Rcan be a large contributor, especially at high tempera-

tures. On the diode that was selected in this design, the current

varies between 1 and 100 μA. It is often advantageous to pick a

diode with a much higher breakdown voltage, just to reduce the

reverse current. Therefore for this example, pick a diode rated for

a V_BDof 60 V, instead of just 40 V.

The output capacitor must have a ripple current rating of at least

500 mA. The capacitor selected for this design is a 4.7 μF 50 V

capacitor with a 1.5 A current rating.

Step 8 Selecting input capacitor. The input capacitor must be

selected such that it provides a good filtering of the input voltage

waveform. A estimation rule is to set the input voltage ripple,

ΔV_IN, to be 1% of the minimum input voltage. The minimum

input capacitor requirements are as follows:

Step 7 Choosing the output capacitors. The output capacitors

must be chosen such that they can provide filtering for both the

boost converter and for the PWM dimming function. The biggest

factors that contribute to the size of the output capacitor are:

PWM dimming frequency and PWM duty cycle. Another major

contributor is leakage current, I_LK. This current is the combina-

tion of the OVP leakage current as well as the reverse current of

the switching diode. In this design the PWM dimming frequency

is 200 Hz and the minimum duty cycle is 1%. Typically, the volt-

age variation on the output, V_COUT, during PWM dimming must

be less than 250 mV, so that no audible hum can be heard. The

capacitance can be calculated as follows:

∆I_Lused

C_IN

(48)

f_SW

0.191 (A)

2 (MHz)

∆V_IN

0.24 μF

0.05 (V)

The rms current through the capacitor is given by:

∆I_Lused

C rms

(49)

0.191 (A)

1 – D(min)

(46)

C_OUT

0.055 A

f_PWM(dimming)

1 – 0.01

200 (Hz) 0.250 (V)

V_COUT

200 (μA)

3.96 μF

A good ceramic input capacitor with a rating of 2.2 μF 25 V will

suffice for this application.

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

1...28 29 303132 33 34

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与A8515相关器件

型号	品牌	获取价格	描述	数据表
A8515GLPTR-T	ALLEGRO	获取价格	The A8515 is a multi-output white LED (WLED) driver for LCD backlighting in consumer and i
A8516	ALLEGRO	获取价格	The A8516 is a multi-output WLED/RGB driver for backlighting LCD monitors and televisions.
A8516ELBTR-T	ALLEGRO	获取价格	The A8516 is a multi-output WLED/RGB driver for backlighting LCD monitors and televisions.
A8516ELPTR-T	ALLEGRO	获取价格	The A8516 is a multi-output WLED/RGB driver for backlighting LCD monitors and televisions.
A8517	ALLEGRO	获取价格	Extensive diagnostics and fault reporting
A8517KLPTR-T	ALLEGRO	获取价格	Extensive diagnostics and fault reporting
A8518	ALLEGRO	获取价格	Fully integrated 42 V MOSFET for boost converter
A8518-1	ALLEGRO	获取价格	Fully integrated 42 V MOSFET for boost converter
A8518KLPTR-T	ALLEGRO	获取价格	Fully integrated 42 V MOSFET for boost converter
A8518KLPTR-T-1	ALLEGRO	获取价格	Fully integrated 42 V MOSFET for boost converter

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