RTC Problem with STM32F429ZIT6

[APAL.1]

With STm32F429ZIT6 the RTC battery used is 3.6V Ni-Cd and the RTC crystal used is 32.768khz. Initially, it works well for some days but after 1-2 months RTC date and time get reset to default value every time system is power reset.

Need help to resolve this ASAP.

Thanks in adcvance.

[TDK]

> Does LIR2032 work?
Go look at the voltage discharge curve of the LIR2032 and compare that against the allowable input voltages of the MCU.

[APAL.1]

Based on the datasheet of STM32F429ZIT6 Vbat pin can support the voltage range from 1.65V to 3.6Vbut when I used a 3V lithium-ion battery RTC was not working. It was getting reset after every power reset.

[TDK]

Batteries do not output a constant voltage. The nominal voltage might be 3V, but that doesn't give you enough information. You need to find a datasheet and look for a discharge curve to see the voltage range.

[MM..1]

Maybe help show schematics, seems as your BAT connection have an issue

[APAL.1]

[APAL.1]

Is this schematic Ok?? or am I doing something wrong?

[APAL.1]

The nominal voltage is 3V and the voltages in the discharge curve are in the range of the acceptable voltage range of Vbat pin as mentioned in the datasheet i.e. 16V to 3.6V. Theoretically, it should work but it is not working and I do use other controllers from ST i.e. STM32F103xx and STM32F107xx as well they are not displaying any issue as shown by this controller. This problem is only with STM32F429ZIT6. I have attached the schematic below for refrence. Please do let me know if i am doing someting wrong.

[MM..1]

More misstake here.
1. NiCd 3,6V is in charged state 1.44x3 = 4,32V >> as allowed for Vbat
2. You try charge 4,3V from 3,3V-diode = never charged
3. On total discharge you see RTC stop work
4. Maybe too your code for F4 reset your RTC, check it

[APAL.1]

Thankyou, I will check the code. Which battery do you suggest using with this?

[MM..1 · Accepted solution]

This is based on how often you plan recharge bat, how long need work system RTC without power etc.
For primary designs with often recharge you don’t need bat, can be used supercap
For long time without power big capacity NiCd is ok (charge from 5V in your circuit) but with conv to 3V3 with low quiescient current around 100nA