AM3359 datasheet(109/236 Pages) TI

109 / 236 page

AM335x

XTALIN

VSS_OSC

XTALOUT

LVCMOS

Digital

Clock

Source

VDDS_OSC

AM3359, AM3358, AM3357

AM3356, AM3354, AM3352

www.ti.com

SPRS717F – OCTOBER 2011 – REVISED APRIL 2013

4.2.2.2

OSC0 LVCMOS Digital Clock Source

Figure 4-10 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 4-10. OSC0 LVCMOS Circuit Schematic

Table 4-4. OSC0 LVCMOS Reference Clock Requirements

NAME

DESCRIPTION

MIN

TYP

MAX

UNIT

f(XTALIN)

Frequency, LVCMOS reference clock

19.2, 24, 25,

MHz

or 26

Frequency, LVCMOS reference clock stability and tolerance(1)

-50

ppm

tdc(XTALIN)

Duty cycle, LVCMOS reference clock period

tjpp(XTALIN)

Jitter peak-to-peak, LVCMOS reference clock period

-1

tR(XTALIN)

Time, LVCMOS reference clock rise

tF(XTALIN)

Time, LVCMOS reference clock fall

(1)

Initial accuracy, temperature drift, and aging effects should be combined when evaluating a reference clock for this requirement.

4.2.2.3

OSC1 Internal Oscillator Clock Source

Figure 4-11 shows the recommended crystal circuit for OSC1 of the ZCE package and Figure 4-12 shows

the recommended crystal circuit for OSC1 of the ZCZ package. 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 is not required and Rd is a 0-Ω 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 has a 10 - 40 k

Ω internal pull-up resistor which is enabled when OSC1 is

disabled. This internal resistor prevents the RTC_XTALIN terminal from floating to an invalid logic level

which may increase leakage current through the oscillator input buffer.

Power and Clocking

109

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