UCC28950EVM-442: Question about function and setting

Hello Satoshi

1/ It's not unusual to see some jitter on the PWM signals. This can come from several sources the main ones being - if there is low frequency ripple on the input voltage to the power stage (2 x line frequency) then the control loop will adjust the duty cycle to maintain a constant output voltage.

If there is some noise on the CS signal then the PWM period can be terminated early or late as the control loop compensates.

2/ D5 and D11 are clamp diodes used to reduce voltage ringing on the secondary of the transformer. Normally they are chosen to carry the full output current and their voltage rating is the input voltage to the power stage plus some margin. They must be ultra fast types - SiC is a good choice.

3/ We don't have a specific layout guideline for magnetics. A few points are worth mentioning. An external screen will reduce the amount of H field interference - grounding the external screen will also reduce the amount of E field noise. Keep the ends of the transformer windings on pins which are close together. If you are using flying leads to make the transformer connections then twist the leads together. This is to reduce the amount of H field interference from the currents in the windings and to a lesser extent to reduce the E field interference. Do not put any sensitive components under the transformer. Talk to the magnetics vendor about how to reduce the Common Mode and Differential mode noise generated by the transformer and about how to minimise the losses in the transformer windings. Some more information is at the TI Power Supply Design Seminars site at  http://www.ti.com/ww/en/power-training/login.shtml  and enter the keyword Magnetics.

Regards

Colin

Colin-san

Thank you for information;

About question-3; If you know something about background of choice EVM's transformer(T3, T4) and inductor(L2), please let me know.

These datasheet is attached below,

56P3362.pdf

60P964.pdf

By the way, is there any information for above(T3, T4, L2) core detailed information?

⇒Core name, internal spec/size, existence insulation tape, core manufacture(or in house?), etc.

I contact and confirming manufacture(Vitec), but reply is not yet.

I think that these Core and package are very high performance, low leak magnetic.

I want to know UCC28950 board need externally care of magnetic field or not. 

Best regards,

Satoshi