Samsung SGH-P400 Service Manual page 6

2. Baseband Circuit description of SGH-P400
1) PSC2106 & LTC 1734
1. Power Management
Seven 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, and 3.0V SIMs,
while a self-resetting, electronically fused switch supplies power to external
accessories. Ancillary support functions, such as an LED driver and two
call-alert drivers, aid in reducing both board area and system complexity.
A three-wire serial interface unit(SIU) provides access to control and
configuration registers. This interface gives a microprocessor full control of
the PSC2106 and enables system designers to maximize both standby and
talk times.
Supervisory functions. including a reset generator, an input voltage monitor,
and a thermal monitor, 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).
2. Battery Charge Management
A battery charge management block provides fast, efficient charging of a
single-cell Li-ion battery. Used in conjunction with a current-limited voltage
source and an external PMOS pass transistor, this block safely conditions
near-dead cells and provides the option of having fast-charge and top-off
controlled internally or by the system's microprocessor.
3. Backlight LED Driver
The backlight LED drivers are low-side, programmable current source
designed to control the brightness the keyboard and LCD illumination.
LED1_DRV is controlled via LED1_[0:2] and can be programmed to sink
from mA to 60mA in 7.5mA steps. LED2_DRV is controlled via LED2_[0:2]
and can be programmed to sink from 5 to 40mA in 5mA steps. Both LED
drivers are capable of sinking their maximum output current at a worst
worst case maximum output voltage of 0.6V. For efficient use, the LEDs
should be forward connected between the ma battery and their
corresponding LED driver output.
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SGH-P400 Circuit Description