Tool/software:
Hi team,
The customer designed flyback using the UCC28740, the following figure is a cut-off HV input test for light loads of two UCC28740 boards.
Customers find that some of the boards’ UCC28740 stops output when VCC drops to UVLO off after the INPUT is cut off, but the VOUT does not output after VCC recovers.
Assumption for the customer: When VCC reaches UVLO on, iso-output does not fall to 0, does that trigger some protection of the IC to turn off VOUT?
My assumption: Customer configuration rated VCC=22V, UVLO on max 23V specified in DS, is there some probabilities of the UCC28740 not turning on at 22V VCC? However, customer feedback: The UCC28740 in the picture below is also able to turn on the 21V VCC. I don't know if UVLO on is a small range change?
Due to the special circumstances, the customer is inconvenient to test more data, and we need to provide some possible conjectures first.
Green: board 1# VCC of UCC28740; Blue: board 2# VCC of UCC28740; Red: board 2# flyback iso-output; Yellow: Vout of UCC28740