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LM22672: Unexpected Output oscillation on some units

Part Number: LM22672

Hi, We've used thousands of LM22672MRE-ADJ in the past to generate 11V from 24V with a very proven circuit design. The switching frequency is 200kHz. Our recent production batch came back having several devices that cause a "hum" in the inductor and the 11V regulated output shows a ~200mVpp oscillation at several kHz. Normally our output is very clean. Once we replace the LM22672-ADJ with a new IC, the hum goes away and the oscillation disappears. The load on the circuit is not changing - its an LED string. It seems the cause for the hum/oscillation is the LM22672 feedback input FB; the humming units seem to have a far larger deadzone. I am wondering what the cause could be? If our board shop didn't use a proper solder profile, would this cause the feedback input performance to change notably? Did TI change anything in the design of wafer fab process recently? Are there any known IC imitations on the market and we ended up with fake LM22672's? How would I verify that I have truly a TI product? It is nearly impossible for me to remove an LM22672 from the pcb without destroying it - so sending one into TI as an RMA is probably not an easy option. I'd appreciate your feedback. Thank you! ~Falk

  • It is possible that a poor solder joint on the ground tab could cause unstable operation.
    If you can take a photo of top of the device so that we can read the top marks we may be able to
    tell you more information. It would be good to see both "good" and "bad" devices.