AM3359 datasheet(98/195 Pages) TI

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AM335x

XTALIN

VSS_OSC

XTALOUT

LVCMOS

Digital

Clock

Source

AM3359, AM3358, AM3357

AM3356, AM3354, AM3352

SPRS717B

– OCTOBER 2011 – REVISED JANUARY 2012

www.ti.com

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 k

Ω 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.

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 Rbias and Rd 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.

Power and Clocking

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AM3359 Datasheet(PDF) 98 Page - Texas Instruments