Counterfeit TOP246PN?

Hello friends,

Since we start to manufacture our power supply using TOP, sometimes we face problems. Last time we begin to make many bench tests and during it our TOP246 blowed up. WE could not understand why, as all measured parameter were correct. We changed the TOP for a new one and then everything came back to normal. But at the time we changed the TOP we notice that the one that had blowed up had a different case marking. We investigeded depply and we found one more model at our factory warehouse, and worst, we found that the chip size from that one that blowed up is smaller than the others. Please, can you help us identify what is the correct, original PI part?