RT117x Driving RTC_XTALI using External oscillator with 1.8V output

[Marwan]

Is it possible to drive RTC_XTALI  with external clock with dc level of 1.8V?
since ensuring that external clock match VDD_SNVS_ANA will increase the design complexity. Also 1.8V is below the absolute  maximum rating of clock inputs.

Marwan_2-1786726380644.png

[Pablo_Ramos]

Hi @Marwan,

As stated in the Hardware Development Guide for the MIMXRT1160/1170 Processor, if you want to feed an external low-frequency clock into RTC_XTALI, the RTC_XTALO pin must remain unconnected or be driven by a complementary signal. The logic level of this forcing clock must not exceed the VDD_SNVS_DIG level.

Additionally, the i.MX RT1170 Crossover Processors Data Sheet states that VDD_SNVS_DIG has an operating voltage range of 0.81 V to 0.95 V, with a typical value of 0.85 V.

This means that a 1.8 V signal would exceed the VDD_SNVS_DIG voltage level.

Best Regard,
Pablo

[Marwan]

Hi @Pablo_Ramos 

There is discrepency in the documents, as mention in other posts.
The datasheet state that it is referenced to VDD_SNVS_ANA.


Kind Regards,

Marwan

[Pablo_Ramos]

Hi @Marwan,

I apologize for the inconvenience.

Your observation is correct, and I will remark this internally.

For now, please refer to the datasheet and ensure that the external clock into RTC_XTALI does not exceed the VDD_SNVS_ANA supply level.

In this case, an external clock with dc level of 1.8V oscillator may be used, as long as VDD_SNVS_ANA is guaranteed to be at or above 1.8 V in the design.

Best Regards,
Pablo

[Marwan]

Hi @Pablo_Ramos,
thanks for your reply,

1 - is there away to guarantee that?
since this power rail is internally generated and there is no mention about whether is it programmable or not.

2 - is there a VDD_SNVS_ANA variance between IC batches?

Kind regards,

Marwan