AM3359 datasheet(109/256 Pages) TI1

109 / 256 page

AM335x

XTALIN

VSS_OSC

XTALOUT

LVCMOS

Digital

Clock

Source

VDDS_OSC

109

AM3359, AM3358, AM3357, AM3356, AM3354, AM3352, AM3351

www.ti.com

SPRS717L – OCTOBER 2011 – REVISED MARCH 2020

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Product Folder Links: AM3359 AM3358 AM3357 AM3356 AM3354 AM3352 AM3351

Power and Clocking

(1)

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

6.2.2.2

OSC0 LVCMOS Digital Clock Source

Figure 6-11 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. The

ground for the LVCMOS clock source and VSS_OSC should be connected directly to the nearest PCB

digital ground (VSS). In this mode of operation, the XTALOUT terminal should not be used to source any

external components. The PCB 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- to 40-kΩ internal pulldown 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 6-11. OSC0 LVCMOS Circuit Schematic

Table 6-4. OSC0 LVCMOS Reference Clock Requirements

NAME

DESCRIPTION

MIN

TYP

MAX

UNIT

ƒ(XTALIN)

Frequency, LVCMOS reference clock

19.2, 24, 25,

or 26

MHz

Frequency, LVCMOS reference clock stability and tolerance(1)

–50

ppm

tdc(XTALIN)

Duty cycle, LVCMOS reference clock period

45%

55%

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

6.2.2.3

OSC1 Internal Oscillator Clock Source

Figure 6-12 shows the recommended crystal circuit for OSC1 of the ZCE package and Figure 6-13 shows

the recommended crystal circuit for OSC1 of the ZCZ package. TI recommends that preproduction 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 preproduction PCBs.

The RTC_XTALIN terminal has a 10- to 40-kΩ internal pullup 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.

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