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RTC backup battery on i.MX6 and MMPF0100

Question asked by Daniele Licini on Nov 17, 2014
Latest reply on Nov 20, 2014 by Pankaj Rana

Dear community,

 

I have developed a board based on i.MX6 Dual Lite and PMIC MMPF0100.

 

I need RTC function.

 

My system hasn't a main battery but is supplied by a wall mount power supply. I need that RTC will keep the time when the main power supply will be disconnected for a little.

So, I have provided a supercap but it seems that it isn't enough.

Now I'm revising my board and I would provide a small lithium rechargable battery.

But, I have some doubts.

 

1) How is the voltage required to mantain RTC time when the main power is OFF? In the i.MX6 datasheet I read  that "Backup battery supply range (VDD_SNVS_IN) is minimum 2.9V and maximum 3.3V". Is it correct?

2) I read that the Maximum supply current of VDD_SNVS_IN is 275uA

 

With the supply current specified (275uA), the small coin lithium batteries (like ML614 or ML621) has a voltage drop and doesn't assure that the voltage will be above 2.9V, even if it is full charged.

 

Should I provide a bigger battery or there is something that I miss?

Onto the SABRE SDP is present a ML414 that for sure can't assure a voltage above 2.9V with a current sink of 275uA.

 

Thanks very much,

Daniele.

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