Fujitsu Stylistic 3500, Technical Reference Manual

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Chapter 7
System Power
This chapter covers the Stylistic 3500 pen tablet’s system power hardware, power management states,
and state transitions.
System Power Hardware 7
The Stylistic 3500 pen tablet 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.
Battery Pack 7
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 pen tablet, the battery pack is charged and the
system is powered by the external source.
The battery pack can also be removed from the pen tablet and charged in an external charger. A bridge
battery built into the pen tablet 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. 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 pen tablet 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.