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Plimit of external FET by TPS2492

Vivekananda dayananda
Prodigy 20 points
Other Parts Discussed in Thread: TPS2492, TPS2493, TPS2393

Application : linear - 28V 6A continuous DC,
Purpose : load protection from UVLO, OV and di/dt & SC.

The power limit set point from calculation (SPREAD SHEET) SLVC033 is set at 84W, while power supply power limit is 168W (APLLICATION LIMIT - 28*6 = 168).

1- THE POWER LIMIT CURVE FORMED IN THE SPREAD SHEET SEEMS TO LIMIT THE VOLTAGE AT 15V,

2- WILL THE DEVICE WORK PROPERLY AT FULL LOAD OF 28V WHEN PLIM IS SET AT 85W ??

 

  • 0
    TI__Genius 14890 points
    Vivekananda,I have moved your post to a different forum for better support.
  • 0
    TI__Mastermind 42795 points
    TPS2492 is designed to protect the MOSFET switch used AND be able to pass the maximum load power. The curve in SLVC033 plots the MOSFET Vds vs. current as controlled by TPS2492. So when Vds is low (normal operating conditions) then the current limit set by 50mV/Rsense applies. But if some fault occurs to increase Vds above 15V then the current limit will be reduced accordingly such that MOSFET power (Vds x I-load) is regulated at 84W.
  • 0 in reply to Eric Wright
    Prodigy 20 points

    Thank you Mr Eric Wright,

    ok got your point, during operation the Vds is very low and Plimit lies within the set Plimit but, does this Power limit, do not affect the start up or the restart feature, as the supply power limit is at 28*6 = 168W which is less than the set limit by TPS2493 at 84W?
    Supply voltage of the application is 28V and 6 A .

    additional
    (The FEt is chosen with current and voltage limits within the SOA and Rds ON as per the SLVC033.
    according to calcuation based on fet characteristics the fet Power limit is 84W while the supply power limit is 168W. )
     

  • 0 in reply to Vivekananda dayananda
    TI__Mastermind 42795 points

    The MOSFET is also protected at start up by the power limit (FET SOA protection) feature. At start up, the assumption is that the output load is not applied (so at start up the 168W load is disabled by the TPS2492 PG pin) and that the only start up FET stress is due to the load capacitor. After the load capacitor is charged, then nPG allows the DC load to pull current through the fully saturated MOSFET. Under this condition, the load can achieve full power of 168W.

    When a load fault occurs, the TPS2492/3 will respond and protect the FET. If the circuit turns off then the nPG pin will disable the load and the hotswap will either latch off or restart (TPS2393).