Using An External 13.00-Mhz Clock; Power Interface; Power Supplies - Intel PXA27 Series Design Manual

Clocks and Power Interface
3.5.1.4

Using an External 13.00-MHz Clock

When using an external clock oscillator to supply the 13-MHz timing, power the oscillator from the
same source driving the VCC_BATT supply input. Connect the oscillator output to the CLK_PIO
pin. Leave the CLK_REQ pin floating or connect it to the external oscillator's output enable input.
During reset, sample the CLK_REQ pin to determine the oscillator configuration. During reset,
when not driven externally, CLK_REQ pulls high internally. When CLK_REQ is pulled high
internally, it allows CLK_PIO to be configured as an input and makes CLK_REQ an active high
output enable to control the external oscillator. Refer to Intel
Mechanical, and Thermal Specification and Intel
Mechanical, and Thermal Specification for CLK_REQ timing specification.
Notes:
•
The oscillator output high drive level must be between 80% of VCC_BATT (0.8 x
VCC_BATT) and VCC_BATT. Similarly, the oscillator output low drive level must be
between VSS and 20% of VCC_BATT (0.2 x VCC_BATT).
•
CLK_REQ must not be pulled high or driven high externally.
3.5.2

Power Interface

To enable low power system design, the PXA27x processor has nine separate power supply
domains for the processor core, memory, and peripherals. All functional units, within a power
domain, connect to the same power supply and are powered up and down together. This
architecture provides flexibility in system configuration (for example, selection of different I/O
voltages for memory and peripherals) and efficient power management (for example, flexibility in
selecting which peripherals are powered at the same time).
In a complete system, there are other components besides the processor such as DRAM and flash
memory, audio CODECs, touchscreen controllers, and specialized companion chips with their own
unique power requirements. In many designs, a highly-integrated power controller supplies power
for the processor and other components, particularly those that interface directly to the PXA27x
processor. An advanced power controller contains circuitry for charging batteries, for powering the
display panel, and includes other analog functions as required by the system. The PXA27x
processor provides several dedicated control signals as well as an Inter-Integrated Circuit (I
interface to communicate with an external power management integrated circuit (PMIC).
3.5.2.1

Power Supplies

A summary of the voltage and tolerance requirements for each external supply input is provided in
®
the Intel
PXA27x Processor Family Electrical, Mechanical, and Thermal Specification. In systems which
dynamically adjust the processor power supply and clock frequency to minimize power, there are
additional requirements for the VCC_CORE power supply. Refer to the Intel
Family Power Requirements Application Note document for more information.
II:3-8
PXA270 Processor Electrical, Mechanical, and Thermal Specification and Intel
®
PXA270 Processor Electrical,
®
PXA27x Processor Family Electrical,
®
Intel PXA27x Processor Family Design Guide
2
C)
®
®
PXA27x Processor