AN024 datasheet(3/7 Pages) AIC

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AN024

GND

VCC

BOOST

AIC1563

470

µF

470

µF

0.1

360pF

µH

1N5820

GF4435

5VOUT/1A

8~12VIN

VOUT

VIN

GND

2.2K

VOUT

VIN

GND

AIC1084-33CM

AIC431

470

µF/6.3V

3.3VOUT/1A

R5 1.2k

3.9k

2.5VOUT/1A

470

µF/6.3V

3.3VOUT/1A

N14

N12

GND

N11

GND

GF4410

1N5401

LL4148

MMBT2222A

Fig. 2 The application circuit for the motherboard of LCD

BOOST

VCC

GND

Oscillator

Comparator

1.25V

Reference

Voltage

Fig. 3 The block diagram of AIC1563.

Components Selection

(1). Current Limit Resistor (R1) Selection

The current limit resistor can be calculated by

following formula:

R1=0.3/ILIMIT

(1)

Since we need a 3A loading at least, the current

limit resistor should be R1=0.3/3A=0.1

Ω.

(2). Oscillator Timing Capacitor (CT) Selection

During the MOSFET turns on, the energy stores

in inductor should be (VIN-VOUT-VQ2,ON)*Ton,

where VQ2,on (0.475V) is the dropout voltage at

MOSFET (Q2) turns on. Similarly, during the

MOSFET turns off, the energy stores in inductor

should be (VOUT+VD2)*TOFF, where VD2 (0.75V) is

the forward voltage of the free-wheel diode D2.

According to the law of the conservation of

magnetic flux, the energy stored in inductor

should be the same at MOSFET turns on and off.

Therefore the relationship can be written as

(VIN- VOUT-VQ1,ON)*TON= (VOUT +VD2)*TOFF

(2)

and the duty cycle is

DUTY

OUT

−

(3)

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