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TPS53515: calculation for max OCL

Henry Kang
Intellectual 1080 points
Part Number: TPS53515

Hi Team,

May i have your help to know how to calculate the max OCL threshold?

the datasheet only shows the 8mΩ parameter for calculating the min OCL but no any others parameters for max OCL.

here is the application condition:

vin 13.5 V
vout 0.83 V
Rtrip 59 kohm
vtrip 0.59 mV
fsw 500 khz
L 1.5 uH
  • 0
    TI__Guru**** 191445 points

    Henry,

    Ideally you could also factor in the tolerance on Itrip (not specified) as well as switching frequency tolerance (not specified) and inductor tolerance in your calculations.

  • 0
    TI__Prodigy 580 points

    Hi Henry, 

    RdsonL is not expected to decrease, so 5.9mOhm is the lowest value to use in OCP calculations. 

    When calculating the worst case Iocp, the only parameter that is a device spec that will change is the RdsonL increasing from 5.9 to 8mOhm. The worst case for RdsonL is provided, because as the part heats up, RdsonL will increase, and can cause the OCP limit to lower. However, the maximum OCP is not something that will change because of the RDSonL changing. To increase the OCP limit, RdsonL would have to decrease, and while the part is operating, the RdsonL is not expected to decrease.

    As a thought experiment, and to be extra thorough, you could test different lower values of RDsonL to see what your worst case would be, but there is not a value lower than the the typical 5.9mOhm that we would expect you to see in any application. 

  • 0 in reply to Alec_Heierman
    TI__Intellectual 1080 points

    Hi John and Alec,

    thanks for your answer.

    now i know how to calculate the max/min OCL threshold, but how about the typical OCL? and as John's replied, can we know the variation of Itrip?

    customer doesn't expect an accurate equation for calculating but just for reference.

  • 0 in reply to Henry Kang
    TI__Prodigy 580 points

    Hi Henry,

    As far as typical OCL, use 5.9mOhm. Because we do not expect RdsonL to drop, typical and max end up being the same. 

    I sent you an email to follow up with your question about Itrip.