User`s guide

Intel
®
StrongARM
®
SA-1110 Microprocessor Development Board User’s Guide 6-1
System Power Management 6
The SA-1110 Development Board is a battery-powered design. It will also run from an AC adapter
that charges the built in batteries or it can draw power from the USB slave port connection.
System power management is a complicated resource management problem that requires
knowledge of all the system resources, as well as an understanding of battery technology and safety
issues.
The following section is intended as a short primer on the SA-1110 Development Board power
system resources and Li-ion battery management basics.
6.1 Battery Power
The main battery is a Lithium Ion (Li-ion) cell of 1000 mAH or greater capacity for a total energy
capacity of 3.6 Watt hours. A Li-ion cell has a fully charged terminal voltage of 4.1 V, a nominal
voltage of 3.6 V and a bottom of charge voltage of 2.5 V.
6.2 Battery Management
The SA-1110 Development Board supports two types of battery and power management: a simple
low-cost scheme and a more expensive smart-battery scheme.
6.2.1 Low-Cost Battery Management
Note: This section provides background information on low-cost battery management issues. The SA-
1110 Development Board supports the hardware implementation of most battery management
functions, however, the software implementation is operating system specific and has not been
fully implemented yet.
The battery terminal voltage may be measured in real time by using the UCB1300 auxiliary analog
to digital converter input AD1. The operating system reads, records and produces histograms
relative to the battery terminal voltage and battery temperature on a fixed schedule of no less than
once per minute.
A battery voltage threshold detect with a hysteresis interrupt circuit is used to interrupt the SA-
1110 via GPIO 26. When the battery hits the hard wired low voltage threshold of 3.5 V, an interrupt
to the SA-1110 is generated. Depending upon the operating system, the system software should
measure the battery terminal voltage using the UBC1300 AD1 and warn the user of the low battery
condition. The hardware for the low-battery interrupt is only active while the LCD is powered up.
The low-battery interrupt scheme requires less software development then the periodic
measurement scheme and is usually a simpler and less sophisticated solution, depending upon the
operating system used. However it does require some system and hardware resources and it does
not provide gas gauging functions.