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LM5060 Does Not Detect Over current During Output Short Circuit to Ground Test

vijay kumar thimmaiah
Prodigy 60 points
Other Parts Discussed in Thread: LM5060

Hello,

We are using Lm5060 in our application as high side switch protection controller. LM5060 is configured for Input Over Voltage protection (Vin > 14V) and Over Current Detection (Iout > 1.5A). timer capacitor value is set as 4,7nF and a external gate Capacitor of 330pF is used to control MOSFET Turn On time. the circuit works fine under normal operating conditions like over voltage protection and over current detection (when output current is increased slowly) but the circuit does not detect over current during output short circuit to ground. during short circuit, LM5060 is supposed to detect over current and Latch OFF the MOSFET until EN pin or VIN pin is reset. but this does not work during short circuit condition. so, the MOSFET turns ON and OFF continiously during the short circuit and until its get damaged. The circuit is attached below for your reference and your support in this regard is highly appreciated.

Thank You

Vijay

  • 0
    TI__Intellectual 2980 points

    Hello Vijay, 

     few questions-

    are you testing it one EVM?

     does your circuit works at 12V ??

     I would need to test your cases once I am back after Nov10 in the office,

     Regards

    Dinesh

  • 0 in reply to Dinesh Kumar6
    Prodigy 60 points

    Hello Dinesh,

    Yes. We are testing on LM5060 Evaulation board. The circuit absolutely works fine under normal operating conditions (EX: 12V Input, Output load of 1.5A). It also detects over current when the load current is increased in steps (slowly) but it does not detct over current when the Output is shorted to ground. With oscilloscope waveform our Initial Analysis shows that during short circuit, the Output current is so high that causes Input voltage to fall below 5.1V (Power On Reset Threshold of LM5060) and resets the latch causing LM5060 toTurn ON MOSFET again..this happens continiously until the MOSFET is damaged. Can you please analyses this in Detail and suggest us a solution for this Problem?

    Thanks in advance

    Vijay

  • 0 in reply to vijay kumar thimmaiah
    TI__Intellectual 2980 points

    Thanks Vijay, 

    I am out of station, will analyse this case once I am back in town.

    Regards

    Dinesh

  • 0 in reply to Dinesh Kumar6
    TI__Intellectual 2980 points
    Hello Vijay,
    Actually LM5060 is designed to provide the over current protection (slow changes).
    The over current detection and protection sequence goes like this-
    Whenever Vds increase the set threshold (as explain in the data sheet “VDS FAULT DETECTION and SELECTING SENSE PIN RESISTOR RS” on page 17 of LM5060.) the timer (time is based on ) will start and after expiry of the timer. It will take another 5us(typically) to pull out the gate in the fault even. and that is very slow process for the short circuit event.
    To limit the output current at desired, please tune the Rs as explain in eq 1, and 2 on page 17 of LM5060 based on the selected MOSFET Rdson.
    Please let me know if you need more information on this.
    Regards
    Dinesh