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AN024 Motherboard Power Supply Using AIC1563
newest technology monitor Flat-Panel Display (FPD). field, widest most grow application Liquid Crystal Display (LCD). many advantages, such light weight, less space, voltage operating power saving. They very attractive. Certainly, brightness, contrast activity transient despondence display, they can't compare with Cathode Tube (CRT) monitor. Fig. shows structure monitor (LCDM), there three main parts motherboard, panel inverter. normal working, monitor needs good power management This application note focus power design motherboard LCD. needs 3.3V 2.5V output voltage, which depend vender's desire. This application note will discuss steps design.
Video
TMDS
Deccoder Timing Controller
Source Driver
Panel
Pads
EEPROM
Adaptor
Power
Panel Power
Inverter
Fig.1 structure
February, 2002
CCFL
Scaler
Gate Driver
AN024
Application
Fig. shows application circuit power management. This application circuit provides 3.3V 2.5V output voltage. uses AIC1563 12V-5V1A outputs. AIC1563 versatile DC/DC converter, designed drive external P-MOSFET generate programmable output voltage. consists internal temperature compensated reference, comparator bootstrapped driver, which drive output switch saturation higher efficiency less heat dissipation. Fig. shows block diagram, following features: input voltage operation. continuous output current. Bootstrapped driver. High side current sense capability. Frequency operation from 100Hz 100kHz. High efficiency 90%). (Pulse Skipping Modulation) control. operate principle when power turn channel MOSFET doesn't turn there feedback voltage. comparator AIC1563 delivers high signal turn bootstrapped driver. this time, connects ground through transistor makes transistor turns channel MOSFET turns input voltage stores energy inductor through output voltage starts rise until feedback voltage between 1.25V. When feedback voltage gets bigger than reference voltage, comparator turns bootstrapped driver off. this time PIN1 floating, voltages collector base terminal transistor same. turns off, then inductor supplies energy output terminal. During turns voltage across input parasitism capacitor approximately zero. there charge path parasitism capacitor, will over temperature. Therefore during turns off, transistor turns provides charge path input parasitism capacitor during turns off. Concerning 3.3V/1A output, AIC1084-33CT achieve easily. function reduce dropout voltage from output AIC1563. there such dropout voltage used, AIC431 with channel MOSFET construct structure with 2.5V output voltage from 3.3V output.
AN024
5VOUT/1A VOUT 47µH MMBT2222A 1N5820 470µF 1N5401 1N5401 3.3VOUT/1A 3.3VOUT/1A AIC1084-33CM VOUT
GF4435 2.2K
GF4410
2.5VOUT/1A
8~12VIN
BOOST
360pF
470µF/6.3V
1.2k 3.9k AIC431
470µF/6.3V
LL4148
470µF AIC1563
Fig. application circuit motherboard
BOOST
Oscillator Comparator 1.25V Reference Voltage
Fig. block diagram AIC1563.
Components Selection
(1). Current Limit Resistor (R1) Selection
current limit resistor calculated following formula: R1=0.3/ILIMIT limit resistor should R1=0.3/3A=0.1. Since need loading least, current should (VOUT+VD2)*TOFF, where (0.75V) forward voltage free-wheel diode According conservation magnetic flux, energy stored inductor should same MOSFET turns off. Therefore relationship written (VIN- VOUT-VQ1,ON)*TON= (VOUT +VD2)*TOFF duty cycle
DUTY VOUT 69.49% VQ2,ON
(2). Oscillator Timing Capacitor (CT) Selection
During MOSFET turns energy stores inductor should (VIN-VOUT-VQ2,ON)*Ton, where VQ2,on (0.475V) dropout voltage MOSFET (Q2) turns Similarly, during MOSFET turns off, energy stores inductor
AN024
switching frequency been 80kHz, then turn-on time
DUTY 69.49% 8.69µS
Consider output current capacity, select 47µH inductor with this case. recommended inductor with magnetic shield reduce magnetic loop.
oscillator AIC1563, typical charging current 25µA voltage amplitude 0.6V. From formula
dVCT
(4). Output Capacitor (C3) Selection
maximum ripple voltage 100mA, then minimum capacitor output terminal obtained
IP(MAX VRIPPLEF 0.5)
written
8.69 361.91pF dVCT
select CT=360pF switching frequency 80KHz.
54.69µF
(10)
where switching frequency, which before. However, output ripple voltage depends (equivalent series resistance)
(3). Inductor (L1) Selection
Owing this application circuit supply three-output voltage, which concludes 5V/1A, 3.3V/1A 2.5V/1A. total loading current working (Continuous Conduction Mode), assuming minimum loading 500mA. Then peak-to peak current amplitude inductor
2IOUT(MIN) 500mA
output capacitor. output ripple voltage maintained
Vripple
(11)
written
VRIPPLE 0.1(
(12)
Thus, select HERMEI series 470µF/6.3V capacitor. minimum loading
maintain
continuous condition mode, minimum value inductor obtained form
VOUT 8.69
written
(MIN)
0.475 21.94µH
AN024
Layout Consideration
There several notes needs considered layout board. components, which follow large current, should placed close possibly reducing loop. each component should placed along direction output current following circuit reducing loss. Each ground should placed same point effectively reduce loop. ground plane shouldn't apart, occur disturbed signals noise. traces, which following large current, should layout width shorten possibly reducing parasitism resistor. Following shows recommend layout this application circuit.
Fig. Layer
Fig. Bottom Layer
Fig. Over Layer
Test Result
Efficiency Test
(mA) 1374 2103 1436 1257 VOUT 4.952 4.949 4.9465 4.943 4.983 4.979 4.9585 4.9585 4.9795 4.976 4.9725 4.97 IOUT (mA) 1000 2000 3000 1000 2000 3000 1000 2000 3000 90.23324 91.10825 90.00182 88.14194 84.40041 87.16737 87.73001 86.32486 82.71595 84.42484 85.68844 84.72554
AN024
Frequency Test
VIN=12V, CT=360pF.
Ripple Voltage Test
VIN=12V, VOUT=5.0V, IOUT=500mA
VIN=12V, VOUT=5.0V, IOUT=1A
VIN=12V, VOUT=5.0V, IOUT=2A
VIN=12V, VOUT=5.0V, IOUT=3A
AN024
step-down step-up DC/DC converter inverting converter. This application note using step-down function AIC1563 cooperates AIC1084-33CT AIC431 achieve power management motherboard. There many application AIC1563 needs discovered.
Conclusion
this application note, main part focuses AIC1563 power design. supply stable output voltage main power motherboard high efficiency light loading (82% upward). used many fields, such constant current source battery charger,

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