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Circuit Description
2-2
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2-2. Baseband Circuit description of SGH-E750
2-2-1. PCF50603 (U405)
- Power Management
Eight low-dropout regulators designed specifically for GSM applications power the terminal and help ensure optimal
system performance and long battery life. A programmable boost converter provides support for 1.8V, 3.0V SIMs,
while a self-resetting, electronically fused switch supplies power to external accessories.
Ancillary support functions, such as RTC module and High Voltage Charge pump, Clock generator, aid in reducing
both board area and system complexity.
I2C BUS serial interface provides access to control and configuration registers. This interface gives a microprocessor
full control of the PCF50603 and enables system designers to maximize both standby and talk times.
Supervisory functions. including a reset generator, an input voltage monitor, and a temperature sensor, support reliable
system design. These functions work together to ensure proper system behavior during start-up or in the event of a
fault condition(low microprocessor voltage, insufficient battery energy, or excessive die temperature).
- Backlight Brightness Modulator
The Backlight Brightness Modulator (BBM) contains a programmable Pulse-width modulator (PWM) and FET to
modulate the intensity of a series of LED’ s or to control a DC/DC converter that drives LCD backlight.
- Clock Generator
The Clock Generator (CG) generates all clocks for internal and external usage. The 32.768 kHz crystal oscillator
provides an accurate low clock frequency for the PCF50603 and other circuitry.
2-2-2. LCD Connector
LCD is consisted of main MAIN LCD, SUB LCD
Chip select signals in the U305, LCD_CS, can enable LCD. BACKLIGHT signal enables white LED of main LCD. These
signal is from U400.
16-bit data lines(LD(0)~LD(15)) transfers data and commands to LCD. Data and commands use "RS" signal. If this signal
is high, Inputs to LCD are commands. If it is low, Inputs to LCD are data. The signal which informs the input or output
state to LCD, is required. But this system is not necessary this signal. So "L_WR" signal is used to write data or
commands to LCD. Power signals for LCD are "VDD_IO_HIGH".
2-2-3. Key
This is consisted of key interface pins KEY_ROW(0:4) and KEY_COL(0:4) in PCF5213EL1. These signals compose the
matrix. Result of matrix informs the key status to key interface in the PCF5213EL1. Power on/off key is seperated from
the matrix. So power on/off signal is connected with PCF50603 to enable PCF50603. Key LED is consisted of
six white
LEDs for sub key and eight white LEDs for main key.
Main and Sub key LED use the
3.3V LDO for a supply voltage. KEY_LED_ON signal enables eight white LED.
