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TPS548B22: Short Circuit Protection

Denny Huang
Expert 7170 points
Part Number: TPS548B22

Dear team 

The customer performed Short Circuit Protection on TPS548B22 and the results shown as below.

CH1 is the output voltage and CH4 is the output current capacity.

1. This is the result of tested during the POL(point of load) is operating.

2. this is the result of tested at the moment the POL is start-up.

1. The customer wonder why there is a step of POL output voltage when Short Circuit condition occurred instead of pulled to low directly?

I have checked TPS548B22 datasheet and not sure if I am correct that the step is caused by UVP. It seems the step duration ~1.2ms is quite match to datasheet that device latches OFF both high/low side MOSFET driver after 1ms so caused the step situation.

2. In addition, why the step only occurred when POL operating condition but not start-up condition?

Would you please confirm?

 Many thanks 

Denny

  • 0
    TI__Expert 7500 points

    Hi Denny,

    Alec will feedback to you soon.

    Thanks,

    Lishuang

  • 0
    TI__Expert 5310 points

    Hi Denny,

    To answer your questions:

    1. When the short circuit is applied, the output voltage falls below the undervoltage protection threshold. At this point, it appears that the customer's load in the short circuit state can sustains some current draw. The device during the 1ms interval following the undervoltage condition, will continue to switch such that the overcurrent protection threshold is not violated, which maintains a charge on the the output caps of 0.5V and sustains the load in this instance. Following the 1ms interval the device's undervoltage protection engages, and the device latches off. The ~0.2ms of additional delay that you highlighted is likely the time it takes the output voltage to discharge to the undervoltage threshold following the application of a short circuit.

    2. After the device latches off following an undervoltage event, a power cycle is needed to reset the fault response of the device. As the datasheet indicates, the UVP engages after soft-start is complete, so an undervoltage event cannot occur during startup. Therefore, we would expect a monotonic startup absent of the apparent "step" seen during an undervoltage event. During startup, there does not appear to be any overcurrent protection occurring as well so the device powers up successfully.

    Regards,

    Alec Biesterfeld