ZEUS Technical Manual

Power and power management

 

 

On-board supplies

There are seven on-board supply voltages derived from the +5V supply. They are listed in the following table:

Supply railPower domainsVoltage

Reset threshold

VCC_BATT

PXA270 Sleep-control subsystem,

3.3V or 3.0V

2.25V

 

oscillators and real time clock

 

 

VCC_CORE

PXA270 core and other internal units

0.85V-1.55V

91% of

 

 

 

nominal

VCC_PLL

PXA270 Phase-locked loops

1.3V

1.18V

VCC_SRAM

PXA270 Internal SRAM units

1.1V

1V

+3V3

PXA270 I/O, PXA270 internal units,

3.3V

3.05V

 

on-board 3.3V peripherals

 

 

VCC_PER

PC/104, Audio Amp, CAN Bus

5V

4.63V

 

transceiver, External GPIO pull-ups

 

(PC/104 only)

VCC_MODEM Zeus Modem

5V

NA

 

 

 

 

Reset will be generated if the supplies fall below the thresholds shown in the table.

VCC_CORE, VCC_PLL and VCC_SRAM rails are controlled by PWR_EN signal of the PXA270. They are switched off when PXA270 is in sleep or deep-sleep mode.

VCC_PER, VCC_MODEM and +3V3 supply rails are controlled by SYS_EN signal of the PXA270. They are switched off when PXA270 is in deep-sleep mode.

VCC_PER rail is also monitored, and reset will be generated to the PC/104 interface if the voltage falls below 4.63V. This can also generate an interrupt on pin GPIO20 of the PXA270.

Power management IC

The Linear Technology device LTC3445 is used to provide the power supply for the PXA270. It is specifically designed for the PXA27x family of microprocessors.

The LTC3445 contains a high efficiency buck regulator (VCC_CORE), two LDO regulators (VCC_PLL, VCC_SRAM), a PowerPath controller and an I2C interface. The buck regulator has a 6-bit programmable output range of 0.85V to 1.55V. The buck regulator uses either a constant frequency of 1.5MHz, or a spread spectrum switching frequency. Using the spread spectrum option gives a lower noise regulated output, as well as low noise at the input. In addition, the regulated output voltage slew rate is programmable via the Power Management I2C interface of the PXA270.

© 2007 Eurotech Ltd Issue D

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