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ZEUS Technical Manual Power and power management
© 2007 Eurotech Ltd Issue D 64
On-board supplies
There are seven on-board supply voltages derived from the +5V supply. They are listed
in the following table:
Supply rail Power domains Voltage Reset threshold
VCC_BATT PXA270 Sleep-control subsystem,
oscillators and real time clock
3.3V or 3.0V 2.25V
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,
on-board 3.3V peripherals
3.3V 3.05V
VCC_PER PC/104, Audio Amp, CAN Bus
transceiver, External GPIO pull-ups
5V 4.63V
(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 I
2
C 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 I
2
C interface of the PXA270.