Chapter 5 System Power; System Power Hardware; Battery Pack - Fujitsu ST4000 Technical Reference Manual

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Chapter 5

System Power

This chapter covers the Stylistic ST4000 Tablet PC's system power hardware, power management states, and state

transitions.

The Stylistic ST4000 Tablet PC uses components designed for low power consumption in mobile applications. DC

power, whether supplied by the battery pack or an external source, is regulated to different voltage levels required to

power various components in the system.

When the system is not connected to external power, system power is provided by the battery pack. When an

external DC power source is connected to the Tablet PC, the battery pack is gradually charged and the system is

The battery pack can also be removed from the Tablet PC and charged in an external charger. A bridge battery built

into the Tablet PC powers the system in suspend mode for approximately 5 minutes while the battery pack is

removed.

Note:

Do not remove the battery pack while the system is running unless an AC Adapter is connected. Suspend

system operation or shut down the system before removing the battery pack. The bridge battery will not power

the system in the Fully On state.

The Tablet PC is equipped with a microcontroller, called the power management microcontroller unit (PMU),

which is dedicated to managing battery pack power. The battery pack charge is monitored by the PMU. The PMU

determines the percent of charge remaining in the battery pack, controls the battery level, and supplies battery status

information to the system through a dedicated interface.

A low voltage level detect circuit (independent of the PMU) measures the battery pack voltage level to determine

whether the battery pack voltage has dropped to the critically low level (the critically low voltage varies depending on

total current draw). When the system is running and the critically low voltage level is reached, the circuit forces the

system into Suspend mode and the battery level window indicates the critically low condition.

When the system is forced into Suspend mode by a critically low battery, the system is powered by the remaining

charge in the battery pack or the bridge battery (whichever has the highest voltage). In this mode, the Suspend/

Resume button is disabled and system operation cannot be resumed until either an external DC power source is

connected or a battery pack with adequate charge is installed.

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