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TPS54202: OCP waveform

Hardy Xue
Expert 3640 points
Part Number: TPS54202

Hi Team,

My customer use TPS54202 on 3V and 5V output application. We are confused about OCP waveform as below. Is TPS54202's OCP behavior normal on 5V OCP waveform?

Test condition:

Vin :7.6V

3V load: 2.8A

5V load: 3.1A

3V OCP waveform:

5V OCP waveform:

Best regards,

Hardy

  • 0
    TI__Mastermind 30621 points

    Hi Hardy,

    What do channel 2 and channel 4 represent? Also, could you test the waveform of SW, VOUT, iL(inductor current) and increase the time scale like 10-100ms/div?

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Expert 3640 points

    Hi Lucai,

    Please refer to below 5V waveform.

    CH2:Vout

    CH3:SW

    Ch4:IL

    Best regards,

    Hardy

  • 0 in reply to Hardy Xue
    TI__Mastermind 30621 points

    Hi Hardy,

    Yes, it's behavior is normal. For TPS54202, if an output overload condition occurs for more than the hiccup wait time, which is programmed for 512 switching cycles, the device shuts down and restarts after the hiccup time of 16384 cycles. 16384 cycles mean 33ms. From your waveform, hiccup off time is approximately 35ms.

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Expert 3640 points

    Hi Lucia,

    Thanks for your reply.

    But my original question is why Output_5V drop to 4V after entering over current condition and then device turn off as my picture before. However, we didn't found the phenomenon at Output_3V waveform. 

    Best regards,

    Hardy

  • 0 in reply to Hardy Xue
    TI__Mastermind 30621 points

    Hi Hardy,

    It is normal.

    The device implements current mode control which uses the internal COMP voltage to control the turn off of the high-side MOSFET and the turn on of the low-side MOSFET on a cycle-by-cycle basis. During each cycle, the switch current and the current reference generated by the internal COMP voltage are compared. When the peak switch current intersects the current reference the high-side switch turns off.

    Thus, as the device is overloaded, the peak current increase until the high side current limit. When this limit is activated, the switch duty cycle is reduced and the output voltage falls out of regulation.  So this is reasonable.

    For output_3V and output_5V, loading is different, so one possibility is that 3V 2.8A loading does not enter high-side current limit and 5V 3.1A loading enters high-side current limit.  Could you also share your 3V Vout waveform and check whether it enters high-side current limit?  

    BRs

    Lucia