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# PMP9766: Problems during the charging operation

Part Number: PMP9766

Hi,

I read the document of PMP9766.http://www.ti.com/lit/ug/slva726/slva726.pdf I want to use this reference design to charge the super-cap. However, during the charging operation, I have some poblems.

In figure 5, during the charging operation, is it constant current charging or constant voltage charging?

How to calculate the charging current?

How to calculate the charging time?

Thank you!

Best Regards,

Wenxiu

### 4 Replies

• Hi Wenxiu,

Could you share your power requirements like Input/output voltage, charging current?

The negative current limit is not specified in the TPS63020 DS.

Please have a look on the new TPS63802. There you can find the negative current limit in the spec.

best Regards,

Michael

• In reply to Michael Helmlinger:

Hi Michael,

I'm learning the document of PMP9766. I'm curious that with the parameters set in the document of PMP9766, during the charging operation, is it constant current charging or constant voltage charging? What is the charging current? And how to calculate the charging time?

In my application, the input voltage is 12V,output voltage is 5.4V and charging current is 1A. PMP9766 can not be applied in my application. But I want to know how is the charging operation of PMP9766 realized.

• In reply to Wendy Wang1:

Hi Wenxiu,

Since the supercap has low impedance the converter runs in current limit. So the charge current gets limited by negative the current limit. See chapter 3.2 in the test report.

Do you need the bidirectional operation or do you just need a step down converter to charge the supercap? Maybe you can share a block diagramm of your application.

best Regards,

Michael

• In reply to Michael Helmlinger:

Hi Michael,

Here is our block diagram.

And it's just the initial plan and we want to find if there is a better one.

Thanks and best regards,

Wenxiu

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