Q&A: i.MX6S minimum level of VDDSNVS_IN for keeping RTC running

Document created by Yixing Kong Employee on Sep 9, 2013
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Question:

What is minimum requirement for VDDSNVS_IN voltage to keep RTC timing info in SNVS block?

In the datasheet, there is requirement for VDDSNVS_IN input and it is 2.9V to 3.3V. Is it recommended requirement for RTC operation?

Other security function is not used in SNVS and just interested in basic RTC fuction after power off.

 

Answer:

 

 

The finall answer is tha to folow our datasheet saying for no matter if you are only RTC keeping application.

"The SNVS regulator takes the SNVS_IN supply and generates the SNVS_CAP supply which powers the real time clock and SNVS blocks. If  VDDHIGH_IN is present, then the SNVS_IN supply is internally shorted to the VDDHIGH_IN supply to allow coin cell recharging if necessary. The output voltage is roughly one third(1/3) of SNVS_IN.
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in the SNVS_CAP powered on-chip logics, need min 0.9v for normal operation, we can only guarantee the operation in this condition, whih means min SNVS_IN = 3*SNVS_CAP = around 2.7. with some margin, so min 2.8v is the requireent. Again, we can only guarantee the operation in this condition(VDD_SNVS_CAP >0.9v).

 

The datasheet is correct : VDDSNVS_IN must not be less than 2.8 V (Table 6. Operating Ranges, of IMX6DQCEC,  Rev. 2.2, 07/2013

 

I guess you talked about operating condition in ON mode. In case of OFF mode, VSNVS output of PFUZE depends on LICELL input power and usually coincell can supply under 2.5V output.

 

According to PFUZE spec, VSNVS output in OFF mode is under 1.8V. And as I know, LP (low power) part of SNVS is only operation al in OFF mode so I don't think VDDSNVS_IN requires over 3V in that condition.

 

In my assumption, SNVS can maintain itis data and RTC if VDDSNVS_IN is over 1.1 ~ 1.3V in OFF mode but I just want to know what is our spec for it.

If we consider low power modes of the i.MX6, then - according to Table 10 (Stop Mode Current and Power Consumption) of IMX6DQCEC, Rev. 2.3, 07/2013 (for example) - in "SNVS Only" mode VDD_SNVS_IN of 2.8V is considered. Here 2.8 V is taken as minimal value. At least, as we can see, there are no other specifications.

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