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UCC2800-EP: Using Overcurrent Detection Feature

Priya Kakarla Naga Lakshmi
Prodigy 130 points
Part Number: UCC2800-EP
Other Parts Discussed in Thread: UCC2800

Hi,

We intend to use UCC2800 just for its internal overcurrent detection feature. Now, we understand that for this feature to work the design has to ensure that the voltage at CS pin has to exceed 1.5V within the blanking period of 50-150ns. For such a fast detection, during overcurrent the primary of the transformer has to go into saturation to ensure the fault is detected reliably. The question is how do we do this? Our transformer design is such that we are operating with lot of margin from saturation. Hence, during overcurrent conditions we are not able to guarantee that CS pin voltage will exceed 1.5V. What design techniques/suggestions/inputs do you have to enable us to use this feature.

Thanks & Regards,

Priya

  • 0
    TI__Mastermind 32805 points

    Priya,

    You are correct! You have normal cycle-by-cycle current sensing happening as a result of peak current mode control. This is happening between the 0-1V CS threshold. The CS input includes internal leading edge blanking (LED) of 100 ns. For the first 100 ns of the CS input, the CS signal is disconnected from the CS comparator and during this disconnect time the second level OCP is providing protection. The second level OCP is also for protection against transformer saturation. This is a very fast OCP that is happening at 1.55V threshold. Even though your transformer is designed with plenty of margin to avoid saturation, what happens if a winding shorts, a VGS or VDS MOSFET failure...you have this second level OCP to protect the power stage from catastrophic failure.

    Regards,

    Steve M