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Damage the synchronous driving pin(SRA/SRB) of UCC28250 when testing input OVP function

Jerry Chen
Expert 5110 points
Other Parts Discussed in Thread: UCC28250, TPS2812, UCC28250EVM-501

My customer is using UCC28250 to design a half-bridge synchronous 150W power. lsolated transformer and driver IC TPS2812 are used for driving secondary synchronous Mosfet IRFB4310. An input OVP function is required and the protection threshold is 141V and recovery threshold is 137.5V. However, when decrease the input voltage from 141V to 137.5V , UCC28250 would enter a hiccup mode and one of the two synchronous driving PIN(SRA/SRB) was damaged(shorted to ground). Then the customer  lower the recovery threshold from 137.5V to 121V, the hiccup mode was disappeared, but sometime the damage of SRA or SRB also happened. The customer wants a threshold of 141V and 137.5V, so I wonder is there any way to protect the SRA and SRB from damage? A capacitor bypass from input of the UC2812 is already used to make a dead-time delay, but the problem still exists.

  • 0
    TI__Mastermind 25130 points

    I will need a lot more information than you are providing to be able to help starting with a schematic.

    regards,

    John

  • 0 in reply to John Bottrill
    TI__Expert 5110 points

    Customer reported a breakdown issue of the SRA/B pin in UCC28250. I have checked it in their lab. The spec is synchronous half bridge. Vin=110 Output=12V/12A. They designed a OVP function of Vin. The issue happens when in OVP: When Vin>=140V, entering OVP. The wanted recovery voltage is 137.5V. However, when Vin comes back to 137.5V, a hiccup happens and SRB is damaged(short to GND). I have just seen this once and the customer said most breakdown issues happened on SRB and SRA was unbroken. The issue happened whenever in heavy or light load. They couldn’t give me the schematic and I cut the structure from our UCC28250EVM-501 as below. The value of OVP resistor is R4=200k R5=1K R44=500Ω. The customer thought it is the hiccup mode damage the SRB, so they have attempted to modify the HICC capacitor(C19), but no improvement. This afternoon, I added a film capacitor(22nF) in parallel with R5 and the hiccup disappeared. However, when changing the capacitor to a 0805 ceramic capacitor, the hiccup happened sometimes(not always). I’ve changed the capacitor bigger(up to 100nF) or smaller, but the issue still existed. It seems that film capacitor(22nF) with 2 leads is able to avoid hiccup. The customer wants to know why the SRB failed when recovery from OVP and why hiccup at this time. They plan to go to the factory and replace the damaged IC with a good one tomorrow, and then check whether the damage still exists in hiccup mode after adding a ceramic capacitor.