Circuit Description - ViewSonic VTMS2431 Service Manual

4. Circuit Description

A/D converter
This brick convert is the 110-220AC input voltage to 24V output for inverter use and 5V for panel ,
system and audio use and 3.3V,1.8V for controller use.
INVERTER
In order to drive the CCFLs embedded in the panel module, there is a half bridge inverter to convert by
the controller.
The input 24V up to hundreds of AC voltage output.
The inverter is formed by symmetric in order to drive the separate lamp modules.
The input stage consists of a PWM controller, half bridge inverter, and switching MOSFET to convert
DC input into AC output.
The output stage consists of a tuning capacitor, coupling capacitor, transformer, push-pull MOSFET
pair to boost AC output up to hundreds of voltage.
And one resister is serial to lamp for output voltage feedback.
There are two signal to control the inverter which come from system.
Logic "high" level which send to I901 is turn on the inverter.
BRI signal control brightness by DC level which was integral from PWM signal.
I206 Scaler MSD2248AL
The MSD2248AL is a highly integrated controller IC for LCD/PDP DTV applications with resolutions
up to full-HD(1920 x 1080). It is configured with an integrated triple-ADC/PLL, a multi-standard TV
video and audio decoder, a motion adaptive video de-interlacer, a scaling engine, the MStarACE-3
color engine, an advanced 2D graphics engine, a transport processor, a high-definition (HD) MPEG
video decoder, a 24-bit DSP for MPEG audio decoding, a DVI/HDCP/HDMI receiver, and a peripheral
control unit providing a variety of HDTV control
functions.
The MSD2248AL comprises an MPEG-2 transport processor with advanced section filtering capability,
an MPEG-2 (MP@HL profile) video decoder, a Dolby  D igital (AC-3)/MPEG layer I and II digital audio
decoder with analog audio outputs that are designed to support ATSC HD/SDTV programs while
handling ATSC CC and EPG.
With additional software support, the MSD2248AL can be used in DVB-T standard areas such as part
of Asia,Africa, and Australia. Furthermore, it is also possible to decode MPEG-4, JPEG, MP3 formats
from external sources such as USB interfaces.
For analog TV, the MSD2248AL includes NTSC/PAL/SECAM multi-standard video decoder
comprising a 3-D motion adaptive comb filter and time-based correction, and a BTSC/A2/EIA-J audio
decoder to support worldwide television standards. In addition, the MStar advanced LCD TV processor
enhances video quality,motion adaptive de-interlacer, picture quality adjustment units, and
MStarACE-3 color engine.
By integrating peripherals including USB 2.0 host controller, UART, IR, SPI, I2C, and PWM, the
MSD2248AL fulfills all requirements in advanced DTV sets.To further reduce system costs, the
MSD2248AL also integrates intelligent power management control capability for green-mode
requirements and spread-spectrum support for EMI management.
PIN DESCRIPTION
Analog Interface
Pin Name Pin Type Function Pin
VCLAMP CVBS/YC Mode Clamp Voltage Bypass 18
REFP Internal ADC Top De-coupling Pin 19
REFM Internal ADC Bottom De-coupling Pin 20
REXT Analog Input External Resister 390 ohm to AVDD_33 13
BIN1P Analog Input Analog Blue Input from Channel 1 21
SOGIN1 Analog Input Sync-On-Green input from Channel 1 22
GIN1P Analog Input Analog Green Input from Channel 1 23
RIN1P Analog Input Analog Red Input from Channel 1 24
BINM Analog Input Reference Ground for Analog Blue Input 25
BIN0P Analog Input Analog Blue Input from Channel 0 26
GINM Analog Input Reference Ground for Analog Green Input 27
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