TMS320F280039C: Why the decoupling cap. for VDD 1.2V has a max?

Wayne Huang

Genius 16375 points

Part Number: TMS320F280039C

Dear Champs,

I am asking this for our customer.

We usually think the larger decoupling cap the better.

In TRM 6.12.1.5.1 Power Management Module Operating Conditions,

Why the cap for VDD has a max spec 26.8 uF?

What will happened if cap total is over the max value?

over 2 years ago

0 Hareesh Janakiraman over 2 years ago

TI__Guru* 95315 points

Wayne,

I will research this and get the answer. May take a few days. On a different note, note that the latest version of this datasheet is SPRSP61B.

0 Hareesh Janakiraman over 2 years ago in reply to Hareesh Janakiraman

TI__Guru* 95315 points

Wayne,

I have had some interactions with the Design team. Will update you before the end of this week.

+1 Joe Prushing over 2 years ago in reply to Hareesh Janakiraman

TI__Genius 15271 points

Hi Wayne, I apologize for the delay getting you a response to this question. The reason for the max capacitance spec is that the internal VREG will take longer to charge a larger capacitor and the result is the device can start executing code (i.e. running BROM) before the VREG output has stabilized into the recommended operating voltage. I hope that clarifies the customer concern.

Note the value should support a standard 22uF +/-20% bulk cap plus some additional small filtering caps if needed.

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TMS320F280039C: Why the decoupling cap. for VDD 1.2V has a max?