UCC2897A: Power management forum

Mike Liu1

Prodigy 80 points

Part Number: UCC2897A
Other Parts Discussed in Thread: PMP5123, PMP3162

Hi...

ucc2897a spec(p16) 8.3.1.14 VDD:one of the references

The capacitance on VREF and VDD should be in a minimum ratio of 1:10.

I want to ask if there is any reason for this?Thanks

6 months ago

0 Hong Huang 6 months ago

TI__Guru 56765 points

Hi,

The reason is to avoid VDD capacitors CDD voltage drop below its UVLO OFF due to transfer CDD stored energy before VDD UVLO ON to VDD UVLO ON as right at UVLO ON, the energy for the device comes nowhere except from CDD which energy will bias the IC and charge up VREF capacitors until an external bias can take over during which time CDD needs to keep its voltage above UVLO ON. This requires CDD value big enough so when consider engineering practice 10 to 1 is recommended,

0 Mike Liu1 6 months ago in reply to Hong Huang

Prodigy 80 points

Hi...

Thank you for answering!!

But i also refer to another design refence: PMP5123

CREF(C29) : CVDD(C28) = 10: 1

This is spical case?! Or another reason?!

Thanks!!

0 Hong Huang 6 months ago in reply to Mike Liu1

TI__Guru 56765 points

Hi,

What about C18 - you cannot ignore this capacitance 220uF which is in parallel with C28 - I believe you overlooked the C18.

0 Mike Liu1 6 months ago in reply to Hong Huang

Prodigy 80 points

Thank you!!

If i want turn on faster!?Can i added green circuit on VDD pin?

See the below (PMP3162)

+1 Hong Huang 6 months ago in reply to Mike Liu1

TI__Guru 56765 points

Hi,

As long as VDD reaches its UVLO ON, the IC will turn on: If your green circuit can do then ok. But this circuit has nothing to do with the 10:1 question. Is your 10:1 question resolved?

For a new and not related you need to create a new thread and if the issue resolved you need to close the thread. These are the rules to work on E2E

0 Mike Liu1 6 months ago in reply to Hong Huang

Prodigy 80 points

OK!!Thank you