PXA3xx Design Guide - Marvell

PXA3xx Processor FamilyDesign GuideFigure 5:TXTAL_IN and TXTAL_OUT Connections to External Clock SourcesTXTAL_IN, TXTAL_OUTconnection to 32.768 kHz crystalTXTAL_IN, TXTAL_OUT connectionto 32.768 kHz clock source22 pFTXTAL_IN32.768 kHzclock generatorTXTAL_IN32.768 kHz22 pFTXTAL_OUTGNDTXTAL_OUT4.4.1.2 Using an External 32.768 kHz ClockWhen using an external clock oscillator to supply the RTC timing, power the oscillator from the samesource that is driving the VCC_BBATT supply input. Connect the external oscillator output to theTXTAL_IN pin. TXTAL_OUT must be grounded.NoteRefer to the Marvell ® PXA30x, PXA31x, and PXA32x Processor Electrical, Mechanical,and Thermal Specification for external 32.768 kHz oscillator-output drive levels.4.4.1.3 Using the On-Chip Oscillator with a 13.000 MHz CrystalThe Marvell ® PXA30x, PXA31x, and PXA32x Processor Electrical, Mechanical, and ThermalSpecification provides specifications for the 13.000 MHz crystal. To use the on-chip crystal oscillator,connect the 13.000 MHz crystal between the PXTAL_IN and PXTAL_OUT pins of the PXA3xxprocessor family. The on-chip oscillator provides the required load capacitance. Therefore, do notconnect external load capacitors to the 13.000 MHz crystal. Place the crystal as close as possible tothe PXTAL_IN and PXTAL_OUT pins of the PXA3xx processor family to minimize PCB trace lengthand capacitance.Route these traces parallel to each other on the same PCB layer. If the 13.000 MHz oscillator outputis used by other components in the system, connect these inputs to the PXA3xx processor familyCLK_POUT output pin, and enable it. Do not attempt to connect an external load directly to thePXTAL_OUT pin.WarningDo not route CLK_POUT or other high-speed digital signals near the 13.000 MHzcrystal or other crystal signals.Doc. No. MV-S301368-00 Rev. A Copyright © 2009 MarvellPage 44 April 6, 2009, Released