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AN024 PDF даташит

Спецификация AN024 изготовлена ​​​​«AIC» и имеет функцию, называемую «For LCD Motherboard Power Supply».

Детали детали

Номер произв AN024
Описание For LCD Motherboard Power Supply
Производители AIC
логотип AIC логотип 

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AN024 Даташит, Описание, Даташиты
AN024
For LCD Motherboard Power Supply Using AIC1563
Introduction
The newest technology of monitor is Flat-Panel Display
(FPD). In FPD field, the widest and most grow up
application is Liquid Crystal Display (LCD). It has many
advantages, such as: light weight, less space, low
voltage operating and power saving. They are very
attractive. Certainly, on the brightness, contrast and the
activity transient despondence of display, they can’t
compare with Cathode Ray Tube (CRT) monitor.
Fig. 1 shows the structure of LCD monitor (LCDM),
there are three main parts in it: motherboard, panel
and inverter. For normal working, LCD monitor needs a
good power management to get in. This application
note focus on the power design for the motherboard of
LCD. It needs 5V; 3.3V and 2.5V output voltage, which
depend on vender’s desire. This application note will
discuss the steps of design.
RGB
DVI
Video
ADC
TMDS
Deccoder
Source Driver
Key Pads
Scaler
MCU
EEPROM
OSD PLL
LCD Panel
Adaptor
LCD MB Power
Fig.1 LCD structure
LCD Panel Power
Inverter
February, 2002
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AN024 Даташит, Описание, Даташиты
AN024
Application
Fig. 2 shows the application circuit for LCD power
management. This application circuit provides 5V,
3.3V and 2.5V output voltage. It uses AIC1563 to get
in the 12V-5V1A outputs. AIC1563 is a versatile
DC/DC converter, designed to drive an external
P-MOSFET to generate a programmable output
voltage. It consists of an internal temperature
compensated reference, comparator and a
bootstrapped driver, which can drive the NPN output
switch to saturation for higher efficiency and less heat
dissipation. Fig. 3 shows the block diagram, and it has
following features:
1. 3V to 30V input voltage operation.
2. 5A continuous output current.
3. Bootstrapped driver.
4. High side current sense capability.
5. Frequency operation from 100Hz to 100kHz.
6. High efficiency (up to 90%).
7. PSM (Pulse Skipping Modulation) control.
The operate principle is when the power turn on; the P
channel MOSFET Q2 doesn’t turn on yet and there is
no feedback voltage. The comparator in AIC1563
delivers a high signal to turn on the bootstrapped
driver. At this time, PIN 1 connects to ground through
a NPN transistor and makes the transistor Q1 turns off
and the P channel MOSFET Q2 turns on. The input
voltage stores energy on inductor through Q2 and the
output voltage starts rise until the feedback voltage
between R3 and R4 get in 1.25V. When the feedback
voltage gets bigger than the reference voltage, the
comparator in IC turns the bootstrapped driver off. At
this time PIN1 is floating, the voltages at collector and
base terminal of transistor Q1 are the same. It turns
Q1 on and Q2 off, and then the inductor supplies the
energy to output terminal.
During Q2 turns on, the voltage across the input
parasitism capacitor of Q2 is approximately zero. If
there is no charge path for the parasitism capacitor,
Q2 will get over temperature. Therefore during IC
turns off, the transistor Q1 turns on and provides a
charge path for the input parasitism capacitor of Q2
during Q2 turns off.
Concerning the 3.3V/1A output, we can use
AIC1084-33CT to achieve easily. The function of D3
and D4 are to reduce the dropout voltage from 5V
output of AIC1563. Due to there is no LDO has such
low dropout voltage can be used, we use AIC431 with
an N channel MOSFET to construct a LDO structure
with 2.5V output voltage from 3.3V output.
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AN024 Даташит, Описание, Даташиты
AN024
VIN
8~12VIN
R1
0.1
+ C1
470µF
8 BOOST DC 1
7 IS DE 2
6 VCC
CF 3
5 FB GND 4
AIC1563
C2
360pF
Q2
GF4435
R2
2.2K Q1
MMBT2222A
D1
LL4148
5VOUT/1A
VOUT
L1
47µH
D2 +
1N5820
C3
R3
470µF 3K
GND
R4
1k
D3
1N5401
D4
1N5401
3.3VOUT/1A N1
AIC1084-33CM
3.3VOUT/1A
3 VIN VOUT 2
GND
Q3
GF4410
1 + C4
470µF/6.3V
R5 1.2k
N14
2.5VOUT/1A
+ C5
R6 470µF/6.3V
N11
GND
N12
GND
UAI3C4313.9k
Fig. 2 The application circuit for the motherboard of LCD
DC 1
Q2
Q1
DE 2
80
QS
R
8 BOOST
7 IS
CF 3
GND 4
CT Is
Oscillator
1.25V
Reference
Voltage
Comparator
+
-
6
VCC
5
FB
Components Selection
Fig. 3 The block diagram of AIC1563.
(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.
(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 =
TON
T
=
VOUT + VD2
VIN VQ2,ON + VD2
= 69.49%
(3)
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