Power on with VDD enable

[sobellinni]

Posted on August 28, 2007 at 14:51

Power on with VDD enable

[anis2399]

Posted on May 17, 2011 at 12:15

Hi sobellinni,

It's mandatory to use an external circuitry to turn ON an OFF the VDD because the VBAT is used only to keep same information in the backup registers and to run the RTC... so if your application will turn OFF the VDD by the STM32(it could be possible), it will be impossible to turn it ON again (exept by external hardware)...

Regards

The Lionheart

[sobellinni]

Posted on May 17, 2011 at 12:15

From AN2586

Battery backup

To retain the content of the Backup registers when VDD is turned off, the VBAT pin can be connected to an optional standby voltage supplied by a battery or another source.

The VBAT pin also powers the RTC unit, allowing the RTC to operate even when the main digital supply (VDD) is turned off. The switch to the VBAT supply is controlled by the power down reset (PDR) circuitry embedded in the Reset block

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No example or methodology is provided for turning on and off the VDD while the part is partially kept alive with Vbat. Do you need EXTERNAL circuitry for this trick?

Art Sobel

[sobellinni]

Posted on May 17, 2011 at 12:15

next question what happens if there is an input signal (+5 volt compatible) [ push button with resistor to VBAT] that is attached to the VBAT supply and then VDD is turned off. Does the input start draining the VBAT? Need to figure this out before layout.