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How to use coin cell (not rechargeable) for RTC with protection diodes

Question asked by nahoko on Aug 19, 2013
Latest reply on Jun 19, 2014 by davecbluechip

Hello,

 

I would like to populate coin cell (not rechargeable) for Real Time Clock on my board which I am designing with i.MX6Q. First I thought single 3.0V coin cell was enough for i.MX6Q. But I can not solve the problem of recharging protection.

 

-VDD_SNVS_IN is required from 2.8 - 3.3V (i.MX6Q datasheet)

-Coin cell voltage (e.g. CR2032) is normally 3.0V.

-Coin cell needs recharge protection. In UL standard, a low leakage diode is recommended as the protection device. The following picture is copied from Panasonic website.

t.bmp

When I put protection diode between coin cell and i.MX6Q, the voltage at VDD_SNVS_IN drops approx. 0.3-0.6V because of V(Forward), so the voltage made by single coin cell does not meet 2.8V.( >3.0V-0.3V)

Does i.MX6Q only intend to use with rechargeable coin cell which may not need a protection diode?

 

I would really appreciate it if you could give me an advice.

 

Thank you.

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