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BQ32000: BQ32000 - Suggested Voltage Rating for Vback Super Capacitor?

Adam Emes
Prodigy 40 points

Part Number: BQ32000

Tool/software:

Hello,

What is the recommended voltage rating for the Vback super capacitor? The datasheet specifies that the Vback voltage can reach Vcc. Vcc in my application is 3.3V - does this imply the super capacitor should be rated for > 3.3V?

I ask because I've seen other forum discussions where people state they are using 3V rated super caps. In the datasheet, a 3V coin cell battery is used (though I know a battery should be okay with >3V at full charge).

For further context, the previous designer for this circuit also was using a 3V super cap. PN I am using has gone end of life, and the only pin to pin alternative is 2.7V rated - is that too low?

Thanks for any support.

  • +1
    TI__Guru** 117000 points

    Hi Adam,

    Unless we close the switch TCFE, otherwise Vback is always smaller than Vcc. If Vcc = 3.3V and the voltage rating of the supercap is 3V, I would say it is rather safe. 

    If the rating is 2.7V, I suggest we add an additional diodes like below. Drawback is when using the supercap as the supply source, Vback is smaller than the voltage rating. 

    Please note, Vback affects the switchover timing.