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UA9638C-EP: Description of Short-Circuit Protection

Vincent Chen64988
Expert 4480 points
Part Number: UA9638C-EP

Hi Team,

Since datasheet doesn't describe how short circuit protection works, my customer would like to know the detail.

Does short-circuit cause heat then trigger thermal protection?

Thanks a lot.

Vincent Chen

  • 0
    TI__Mastermind 25705 points

    Vincent,

    The short current is limited by the internal resistor (9.6Ohm typical) as shown in Figure 4 on the datasheet. The shorting itself may or may not trigger the thermal protection. Depending on the short current value and ambient temperature, you can use the thermal information to estimate the junction temperature, which determines if the thermal protection is enabled. Please let me know if it makes sense to you.

    Regards,

    Hao 

  • 0 in reply to Hao L
    TI__Expert 4480 points

    Hi Hao,

    My customer wants to use short circuit protection feature in his system, what we understand is when one of output pins is shorted to ground then short circuit protection will be triggered and shut down UA9638C. But the customer test result is not as our expected.

    Here is customer's SCH. Our thought is drive UA9638C pin 3 always to high then pin 6 will be at high level as well, connecting pin 6 to ground directly then this part will entry to shot down mode. Customer used this approach to check short circuit protection function works on not.

    Below is the test result.

    CH1: PULSE_O0_B is always drive high level. (means UA9638C pin 3 is at high level)

    CH2: U136.6 is connected to ground.

    CH3: Feed PWM signal into PULSE_O0_A,  AXIS_O0_A#( U136.7) is still work. UA9638C is still at active status, not enter to shut down mode.

    That is why customer wants to know what is the short circuit protection working principle. And why he shorted output pin but it seems nothing happen. Could you please comment this behavior? 

    Thanks a lot.

    Vincent 

  • 0 in reply to Vincent Chen64988
    TI__Mastermind 25705 points

    Vincent,

    Thanks for your explanation and data. Unfortunately as I mentioned before, the customer might not be able to see the device enter the thermal shutdown mode by shorting the bus. Assume the device consumes about 200mA (45mA + 150mA) in the short condition, which is about 1W with 5V Vcc. According the datasheet, the power rating at 25c is 725mW. You can see the shorting in this case is at the edge of the triggering. The customer can try to increase Vcc or temperature to see if it makes any difference. The proper way to check Ios is by biasing the input voltage to the abs max (-0.5V in this testing) to see the current exceeds the spec on the datasheet. Please let me know if you have more questions.

    Regards,

    Hao