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TPS53355: current limit

Yuta Nishie
Genius 5280 points
Part Number: TPS53355


Hi,

1) How many seconds above the current limit set by the 21pin does overcurrent protection start to work?

2) What is the unit for each parameter in equation (2) on datasheet P18?

Best Regards,

Nishie

  • +1
    TI__Genius 11805 points

    Hey Nishe,

    Overcurrent protection is handled through a comparator that measures the voltage across the low-side FET during "off time" and applies an extension to the "off time" until the current level falls below the threshold. This means that the current protection is cycle by cycle, so the maximum time for OCP protection would be the period of a switching frequency. Time = 1/Fsw.

    Units in the equation are standard SI units unless otherwise noted. (Volt, Ohm, Amp, Hz, Inductance).

    Please click "this resolved my issue if I have answered your questions.

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Genius 5280 points

    Hi Caleb-san,

    Thank you for your reply.

    1) I understand that the maximum time for OCP is "Time = 1/Fsw".

    Am I correct in my understanding that the minimum time will be the same as the Off time for Low-side FET? ”Time(min)=1/Fsw(off)”.

    Or does OCP work if the current limit threshold is exceeded even for a moment?

    2) Is the following unit correct?

    VTRIP is mV, RDS (on) is mΩ, IIND (ripple) is mA, L is uH, fsw is kHz, VIN and VOUT are V.

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Mastermind 32420 points

    Hello Caleb is OoO today, he will respond on Next week. 

  • 0 in reply to Tahar Allag
    Genius 5280 points

    Hi Tahar-san,

    I look forward to your reply.

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Genius 12405 points

    Thanks!

    Caleb will respond in a few days

  • +1 in reply to Yuta Nishie
    TI__Genius 11805 points

    Hello Nishie,

    The current is measured when the Low-side FET is ON (current is passing through it). So, if OCP is hit when the HS FET is on and the LS FET is off, then the OCP will not be recognized until the HS FET is OFF and the LS FET is ON. The LS FET will stay on as long as there is an OCP condition.

    In regards to your second question: VTRIP (V), RDSon (Ohms), IIND(Ripple) (A), L(H), FSW(Hz), VIN and VOUT are V.

    Thanks,
    Caleb