ViewSonic VE710b-4 Service Manual page 16

an external pull up resistor.
A "8051 standard pin" is a pseudo open drain pin. It can sink at least 4mA current when output is at low level, and drives at least 4mA current
for 160nS when output transits from low to high, then keeps driving at 100uA to maintain the pin at high level. It can be used as input or output
function. It needs an external pull up resistor when driving heavy load device.
POWER CONFIGURATION
The MTV312M can work on 5V or 3.3V power supply system.
In 5V power system, the VDD pin is connected to 5V power and the VDD3 needs an external capacitor, all
output pins can swing from 0~5V, input pins can accept 0~5V input range.
And ADC conversion range is 5V. However, X1 and X2 pins must be kept below 3.3V.
In 3.3V power system, the VDD and VDD3 are connected to 3.3V power, all output pins swing from 0~3.3V, HSYNC, VSYNC and open drain
pin can accept 0~5V input range, other pins must be kept below 3.3V. And the ADC conversion range is 3.3V.
C. 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 12V 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.
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