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LM2852 Theory of Operation

David Lamensdorf
Prodigy 20 points
Other Parts Discussed in Thread: LM2852, LM2854

Hello,

I am trying to find some information on the LM2852 that specifically addresses its short circuit protection circuitry. Is there a theory of operation overview? The datasheet does not go into this depth of technical discussion.

Thank you,

David Lamensdorf

Safe Environment Engineering

  • 0
    TI__Genius 11085 points

    I've forwarded your question to the responsible engineer. Hope he will get back to you soon.

    I found a description of short circuit protection in the LM2854 datasheet. I believe they are the same family of parts with the same protection strategy. LM2852 peak current limit typical values are 4A in X version and 3A in Y version based on the EC table.

    "POSITIVE CURRENT LIMIT
    The LM2854 employs lossless cycle-by-cycle high-side current limit circuitry to limit the peak current through the
    high-side FET. The peak current limit threshold, denoted ICL, is nominally set at 6A internally. When a current
    greater than ICL is sensed through the PFET, its on-time is immediately terminated and the NFET is activated.
    The NFET stays on for the entire next four switching cycles (effectively four PFET pulses are skipped). During
    these skipped pulses, the voltage on the soft-start pin is reduced by discharging the soft-start capacitor by a
    current sink on the soft-start pin of nominally 6 µA or 14 µA for the 500 kHz or 1 MHz options, respectively.
    Subsequent over-current events will drain more and more charge from the soft-start capacitor, effectively
    decreasing the reference voltage as the output droops due to the pulse skipping. Reactivation of the soft-start
    circuitry ensures that when the over-current situation is removed, the part will resume normal operation smoothly."

    Hope this helps.

    Yang

  • 0
    Prodigy 20 points

    Hello,

    I would greatly appreciate hearing back from your Engineer specifically regarding the the LM2852 and its short circuit protection. Our product is currently in laboratory testing for an intrinsic safety rating so that it can be used in potentially explosive environments. The Engineers performing the testing are requesting more detail on this parts protection circuit.


    Very much appreciated,

    David Lamensdorf

    Safe Environment Engineering

  • 0 in reply to David Lamensdorf
    TI__Genius 15810 points

    Hello David, 

    The LM2852 core is the same as the LM2854. Therefore everything that Yang mentioned in the above post should apply to the LM2852 as well. Let me know if this information helps. What specific more information would you like on the devices? 

    Regards,
    Akshay