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TPS65235: TPS65235 current limit question

Hermes Lin1
Intellectual 420 points
Part Number: TPS65235

hi sir:

We have question about LNB current limit. we base on datesheet to calculation the current limit. Currently, our l_set resistor is 287K with I_ocp 0.48A.
But this current protection point are different, when 22KHz-Tone enable and disable.

Our verify result as below table
22KHz-Tone
Vout         Disable               Enable
13.4V      OCP = 0.46A       OCP = 0.39A
18.2V      OCP = 0.46A       OCP = 0.39A

When the 22KHz-Tone is enable, the current protection point seem don’t meet calculate formula.
We also verify the TPS65235 EVM and happen the same phenomenon.
The project request is "must be meet output current 400mA."(even if the 22KHz-Tone is enable.)\

  • 0
    TI__Genius 15135 points
    Hi, Hermes

    The OC limit is not related with tone, how do you enable the 22kHz tone?

    BTW, the calculted OC limit is not accuracy, suggest to leave some margin between max Iout=400mA and min OC limit.
  • 0 in reply to Zhao Ma
    Intellectual 420 points

    hi Zhao Ma:

    customer used Pin_13 EXTM to enable/disable the 22kHz tone for testing.

    the Pin_13 EXTM setting will cause the current setting error?

    How much tolerance for design margin?

  • 0 in reply to Hermes Lin1
    TI__Genius 15135 points
    Hi, Hermes

    1. I have double checked on EVM.
    When EXTM=low or high, the OC threshold is same, the EXTM signal will no affect the OC limit.
    My test method:
    Hard short VOUT to GND, probe the output current by oscilloscope.
    So, what is your test method?

    2. Suggest to leave 50% margin.
    For example, the max Iout=400mA, recommend to set typical OC limit =600mA.