Contradiction on DS and UM of QN902X regarding RTC crystal oscillator selection

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Contradiction on DS and UM of QN902X regarding RTC crystal oscillator selection

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szlittle
Contributor II

Hi all,

I am planning to use QN902X for my application. Regarding the RTC crystal oscillator, It seems a contradiction in DS and UM. 

In DS, it mentioned that a 32.768Khz crystal should be used while UM(Page 70) said it should be 32Khz. 

A clarification would be highly appreciated.

Li Yongyong

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estephania_mart
NXP TechSupport
NXP TechSupport

Hello, 

The 32 kHz it's being used as an abbreviation for the 32.768 kHz. 

In the same UM you can see several references as 32 kHz (32.768 kHz), you can check as well the Figure 7 Clock block diagram in the UM. 


Regards, 

Estephania

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szlittle
Contributor II

Hi Estephania,

Thanks for your reply. 

I don't think the 32Khz in Page 70 of UM is a abbr. of 32.768Khz.

Quote:"The RTC is composed of two counters. The first one is the 15-bit 1-second counter, which runs at 32 kHz clock and wraps to 0 once it reaches 32000 corresponding to the 1- second interval. The second one is the 32-bit counter, which is triggered by the first counter and can last for years with 1LSB representing one second."

Please see how the counter runs--- it will be cleared to 0 when reaches "32000", instead of "32767".

Thank you.

Li Yongyong

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