User manual

ZEUS user manual

Issue E

Battery backup

An on-board non-rechargeable coin cell battery (CR2032) provides a 3V battery backup

supply for the ISL1208 RTC, external SRAM and the supply supervisor, when there is no

+5V supply to the board. The ZEUS is normally shipped with battery disconnected. See

JP2 – Battery disconnect

, page 85, for details.

The table below shows the typical and maximum current load on the backup battery:

Device load on battery Typical (µA) Maximum (µA)

SRAM 0.3 3

ISL1208 RTC (with Clock Out Off) 0.4 0.95

Supply Supervisor 0.5 0.5

Total 1.2 1.45

An onboard Schottky diode drops 13mV from VBAT at +25°C (+77°F). At -40°C

(-40°F) this may increase to 170mV and at +85°C (+185°F) it may decrease

below 10mV. The SRAM and ISL1208 minimum voltages are 1.5V and 1.8V

respectively. Reliable operation below these minimum voltages cannot be

guaranteed.

Processor power management

First available in the PXA270 processor, Wireless Intel SpeedStep Technology

dynamically adjusts the power and performance of the processor based on CPU

demand. This can result in a significant decrease in power consumption.

In addition to the capabilities of Intel Dynamic Voltage Management, the Intel XScale

micro architecture of the PXA27x family incorporates three new low power states. These

are deep idle, standby and deep sleep. It is possible to change both voltage and

frequency on the fly by intelligently switching the processor into the various low power

modes. This saves additional power while still providing the necessary performance to

run rich applications.

Wireless Intel SpeedStep technology includes the following features:

• Five reset sources: power-on, hardware, watchdog, GPIO and exit from sleep and

deep-sleep modes (sleep-exit).

• Multiple clock-speed controls to adjust frequency, including frequency change, turbo

mode, half-turbo mode, fast-bus mode, memory clock, 13M mode, A-bit mode and

AC ’97.

• Switchable clock source.

• Functional-unit clock gating.

• Programmable frequency-change capability.

• One normal-operation power mode (run mode) and five low power modes to control

power consumption (idle, deep-idle, standby, sleep and deep-sleep modes).

• Programmable I

C-based external regulator interface to support changing dynamic

core voltage, frequency change and power mode coupling.