UCC2897A: The waveform is not normal

Vickers

Intellectual 980 points

Part Number: UCC2897A

Hello all,

UCC2897 this chip power output 12V, a lot of ripple when powering up.

Channel1 is DC 12V input:

waveform of SS pin:

over 5 years ago

0 John Griffin1 over 5 years ago

TI__Mastermind 34465 points

Hello Vickers,

What are the waveforms shown in your second scope plot ?

CH 2 is ?

CH 1 is ?

Regards

John

0 Vickers over 5 years ago in reply to John Griffin1

Intellectual 980 points

Hi John,

Picture 1 Ch1 is DC input 24V

picture 2 Ch1 is SS PIN

0 Vickers over 5 years ago in reply to John Griffin1

Intellectual 980 points

Hello John,

FB pin waveform when power is less than 2W:

MOS VGS waveform when power is less than 2W:

is this normal?

0 John Griffin1 over 5 years ago in reply to Vickers

TI__Mastermind 34465 points

Hi Vickers,

What you are seeing here is a burst type of operation at very light loads.
At very low loads the FB signal is very small and the controller starts missing pulses because of the narrow pulse width.
This causes a resulting burst in pulses as the controller attempts to set the correct output voltage.
The burst waveforms you are seeing are normal at light loads.

Regards

John

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UCC2897A: The waveform is not normal