UCC28780: UCC28780 PWML

user5781628

Intellectual 970 points

Part Number: UCC28780

Hi,

The PWML is supposed to be turned on when the primary transformer current just reaches to 0A. Right?

But I found that the PWML is turned on after PWMH turned off about 160us. Could you help explain why?

Is it possible that the TDM time is too long?

It works at 2pulses in ABM, what decides the first TDM of the of every burst packet in ABM?

Test condition: Vin=165Vdc, Vout=5V; Iout=2A;

CH1:RUN; CH2:PWML; CH3:VSW; CH4:Ipri;

over 6 years ago

0 Hong Huang over 6 years ago

TI__Guru 74115 points

CH2 PWML, can you label PWML turn-on time instant. Your cursors 164ns should be PWML turn off point. Can you check the waveform and your statement to make alignment between.

0 user5781628 over 6 years ago in reply to Hong Huang

Intellectual 970 points

Please see the below picture: CH1:RUN; CH2:PWML; CH3:VSW; CH4:Ipri;

PWML should be turned on just Ipri reaches 0A, right?

But now in this picture, PWML is turned on at high negative Ipri current.

What cause this phenomenon? Is theres any relationship with the RDM setting?

0 Hong Huang over 6 years ago in reply to user5781628

TI__Guru 74115 points

It looks your TZ time is not long enough. If you increase RTZ, the PWML should turn on with more delay so at a less negative Ipri. You can refer the datasheet page 19 and Figure 18. Please make sure ZVS when you tune RTZ and RDM.

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UCC28780: UCC28780 PWML