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TPS51285B: TPS51285B OCP settings

jerry lee12
Prodigy 120 points
Part Number: TPS51285B

Hi sir:

TPS51285B OCP design.

Protection point for Iout: 10A , How do I design?

Spec content description, but not very understand.

Thanks

.

  • 0
    TI__Mastermind 18510 points

    Hi Jerry,

    First, You can calculate the ocp based on formular 3+4. The IOCL is the OC point.

    From the formular, we can get If Vin, Vout and LC circuit are fixed, the OCP will depend on Rdson of low side mosfet and  CS pin resistor(RCS), and if MOSFET is fixed as well, you can only tune RCS to get the OCP point that you want, I recommend you set OCP at (1.5~2)Iout, and of course you also need care about the ID of mosfet and indcutor current ability, and even Vinput source current ability need to be considered.

  • 0
    TI__Expert 6425 points

    Hi Jerry,

    In order to provide both good accuracy and cost effective solution, the device supports temperature compensated MOSFET RDS(on) sensing. So you should set Rcs. You can do following below step. you also can refer DS page 18.

    1, set I(OCL_DC). for example: you set 10A.

    2, calculate ripple, Please use equation: Iripple= (Vin-Vout)x Vout/(L x fsw x Vin).

    3, calculate Vtrip. Vtrip=Rds(on) x (Iocl_dc-Iripple/2). In the equation, Rds(on) is low side Rds(on).

    4, calculate Rcs. Rcs =8 x (Vtrip-1mV) /Ics. Ics is 50uA. please pay attention, Confirm Vcs voltage is within the range of 0.2 V to 2 V over all operation temperature using below equation: Vcs=Ics x Rcs{(25-TA)x0.0045-1}. where TA is an operation temperature.

    best regards.