AM3359 Datasheet, PDF (95/162 Pages) Texas Instruments – AM335x ARM Cortex-A8 Microprocessors (MPUs)

AM3359, AM3358, AM3357
AM3356, AM3354, AM3352
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SPRS717 – OCTOBER 2011
4.2.2.2 OSC0 LVCMOS Digital Clock Source
Figure 4-7 shows the recommended oscillator connections when OSC0 is connected to an LVCMOS
square-wave digital clock source. The LVCMOS clock source is connected to the XTALIN terminal. In this
mode of operation, the XTALOUT terminal should not be used to source any external components. The
printed circuit board design should provide a mechanism to disconnect the XTALOUT terminal from any
external components or signal traces that may couple noise into OSC0 via the XTALOUT terminal.
The XTALIN terminal has a 15 - 40 kΩ internal pull-down resistor which is enabled when OSC0 is
disabled. This internal resistor prevents the XTALIN terminal from floating to an invalid logic level which
may increase leakage current through the oscillator input buffer.
XTALIN
AM335x
VSS_OSC
XTALOUT
LVCMOS
Digital
Clock
Source
Figure 4-7. OSC0 LVCMOS Circuit Schematic
4.2.2.3 OSC1 Internal Oscillator Clock Source
Figure 4-8 shows the recommended crystal circuit. It is recommended that pre-production printed circuit
board (PCB) designs include the two optional resistors R_bias and R_d in case they are required for proper
oscillator operation when combined with production crystal circuit components. In most cases, Rbias will
not be required and Rd will be a zero ohm resistor. These resistors may be removed from production PCB
designs after evaluating oscillator performance with production crystal circuit components installed on
pre-production PCBs.
The RTC_XTALIN terminal does not enable an internal pull-down resistor when OSC1 is disabled. If this
oscillator is disabled, the RTC_XTALIN terminal may float to an invalid logic level which may increase
leakage current through the oscillator input buffer. This should not be an issue for most applications that
use this oscillator to source the RTC clock since the RTC requires a continuous clock to maintain time.
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Power and Clocking
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