IMX6 32kHz Design Considerations

[bomsweigh]

Hello,

We are developing an IMX6 Solo/Quad common design and have seen a reference that states that applying a 32.768kHz external clock to RTC_XTAL1 can reduce boot time.  I cannot find an ap-note that describes this or addresses possible concerns.  Reading this forum and t6eh datasheetss, we see that the main considerations are that VDD_SNVS is powered, POR_B remains asserted until the clock is stable, XTAL0 left floating with a clock in to RTC_XTAL1, and that the peak amplitude of the clock must not exceed VDD_SNVS.

We would like to ask a few questions.

1 - does the use of an external 32kHz clock improve boot time?

2 - are the assumptions above correct?

3 - does the input to RTC_XTAL1 need to be AC coupled and is a series resistor required?

4 - are there other aspects to implementing an external 32k clock that NXP recommends or an AP note or reference design I should have referenced?

Thanks for your consideration,

BW

[igorpadykov]

Hi BOMS

since 32kHz crystal may have significant start-up times,

providing it externally can improve boot time.

No need for AC coupling, recommendations are provided in

Table 2-7. Oscillator and clock recommendations

i.MX6 System Development User’s Guide

http://cache.freescale.com/files/32bit/doc/user_guide/IMX6DQ6SDLHDG.pdf

Best regards

igor

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