AM4376 datasheet(136/261 Pages) TI

136 / 261 page

Device

RTC_XTALIN

RTC_XTALOUT

N/C

LVCMOS

Digital

Clock

Source

VDDS_RTC

VSS_RTC

AM4376, AM4377, AM4378, AM4379

SPRS851B – JUNE 2014 – REVISED APRIL 2015

www.ti.com

5.12.2.3.4 OSC1 LVCMOS Digital Clock Source

Figure 5-15 shows the recommended oscillator connections when OSC1 of the package is connected to an

LVCMOS square-wave digital clock source. The LVCMOS clock source is connected to the RTC_XTALIN

terminal. In this mode of operation, the RTC_XTALOUT terminal should not be used to source any external

components. The printed circuit board design should provide a mechanism to disconnect the RTC_XTALOUT

terminal from any external components or signal traces that may couple noise into OSC1 via the RTC_XTALOUT

terminal.

The RTC_XTALIN terminal has a 10 - 40 k

Ω 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.

Figure 5-15. OSC1 LVCMOS Circuit Schematic

Table 5-18. OSC1 LVCMOS Reference Clock Requirements

NAME

DESCRIPTION

MIN

TYP

MAX

UNIT

Frequency, LVCMOS reference clock

32.768

kHz

Maximum RTC error =

-20

ppm

f(RTC_XTALIN)

10.512 minutes/year

Frequency, LVCMOS reference clock

stability and tolerance(1)

Maximum RTC error = 26.28

-50

ppm

minutes/year

tdc(RTC_XTALIN)

Duty cycle, LVCMOS reference clock period

tjpp(RTC_XTALIN)

Jitter peak-to-peak, LVCMOS reference clock period

-1

tR(RTC_XTALIN)

Time, LVCMOS reference clock rise

tF(RTC_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.

5.12.2.3.5 OSC1 Not Used

Figure 5-16 shows the recommended oscillator connections when OSC1 is not used. An internal 10-k

Ω pullup on

the RTC_XTALIN terminal is turned on when OSC1 is disabled to prevent this input from floating to an invalid

logic level which may increase leakage current through the oscillator input buffer. OSC1 is disabled by default

after power is applied. Therefore, both RTC_XTALIN and RTC_XTALOUT terminals should be a no connect

(NC) when OSC1 is not used.

For more information on disabling OSC1, see the device-specific technical reference manual.

136

Specifications

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