Hi guys,
I am working with UCC28950 controller applied to phase-shifted full bridge DC/DC converter (PSFB). I am experienced in that field and UCC28950, I have used this chip in severals projects with outstanding outcomes. My PSFB is works with 270 V (input voltage) to yield 48 V (output voltage) with peak current control (input current loop). I work with several PSFB in parallel. The problem I firstly have found is that voltage SS/EN pins falls down below normal operation voltage (about 4.65 V) in one of the converters that works in parallel, let me explain better:
- I use a high voltage source to generate 270 V. When this voltage accomplishes about 100 V the output voltage is clamped (controlled) to 48 V, my output voltage refrerence because I use a 1:2 high frequency transformer. When the input voltage is among 150 V an 270 V the SS/EN pins fall down below normal operation voltage (about 4.65 V) and starts to oscillate (about 1 V to 3 V). However the output voltage follows in 48 V but if I try to supply current the output voltage falls down uo to 0 V. I have checked the VREF and VDD pin and are OK but the SYNC pin is fallen down when SS/EN is down. I can solve this situation when the output current is a big step (for example from 0 A to 5 A) as a results the SS/EN is clamped to normal operation voltage, now the converter can work in any range of current (from 0 to max current). Very extange.
- Anther anormal situation that I hafve found is that when I work with several PSFB in parallel is that sometimes some of the ouputs of the chip, for example outputs OUTA and OUTB, are fallen down even when the SS/EN pin are in normal operation voltage.
What situations can cause a drop voltage in SS/EN?
Is it a noyse (EMC) problem?
Could someboy give me some advices?
Has somebody have this troubles?
I am looking forward to hearing from you,
Best regards,
Manuel