STM32H7S7L8H6: VBAT connection

[JK1234]

Hello Team,

Query related to VBAT. Please refer below capture and provide your feedback for VBAT. Diode D1 and other components are, ok? 

Thanks & Regards,

Jignesh Karena

[TDK]

Power dissipated by R218 if C56 is 0V is around 1.5 W which greatly exceeds the rated power value. Is C56 okay being charged at 500 mA? Can your 3.3V rail even supply that much excess current?

Generally want a much slower charge rate by increasing R218.

Diode reverse current seems a bit high. Probably better choices, but maybe it's good enough for your application.

[JK1234]

Hello @TDK ,

Thanks for updates.

Can you please suggest best diode for this?

If we do not use R218 and connect direct connect it with VBAT pin via D1 diode than it is, ok? Refer below image.

Thanks & Regards,

Jignesh Karena 

[KDJEM.1]

Hello @JK1234;

I recommend you to look at AN5935 application note Table 4. Power supply connection and Figure 3. Power supply component layout. The values of the two capacitors are 1 µF ceramic and 100 nF not 1F and 100 nF.

Thank you.

Kaouthar

[JK1234]

Hello @KDJEM.1 ,

We want to use this solution for RTC. So, here 1F is super capacitor.

So, can you please provide some reference design for RTC using super capacitor?

Thanks & Regards,

Jignesh Karena

[JK1234]

Hello Team,

Waiting for your feedback.

Thanks & Regards,

Jignesh Karena

[KDJEM.1]

Hello @JK1234 ;

Do you need more hardware information about how to retain the content of the RTC backup register?

Please look at 3.5 Battery charging domain.

Thank you.

Kaouthar

[TDK]

Do you have tools available to simulate this circuit? I suggest using those to see the effect of removing R218.