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Original question:

TIDA-01605: Short-Circuit detection circuit explanation, user guide page 9

TIDA-01605: query in short circuit sense circuit & short circuit time setting in TIDA-01605

naga sahitya
Intellectual 550 points
Part Number: TIDA-01605
Other Parts Discussed in Thread: TL431,

Hiii TI Team,

                           I have a query in short circuit sense circuit & short circuit time setting. when there is a short circuit , the voltage across drain to source is almost dc link voltage( assume the voltage  drop across leakage inductance is zero). In this case D6 is reverse biased , D5 also reverse biased, so R15 & R18 will be in series & its effective value will be 15.1k(10k + 5.1k). I am ignoring D8 for simplifying calculation. ,  R25 & R26 are in parallel & its effective value will be 2.55k ( 5.1k// 5.1k). The time constant of the equivalent circuit is (15.1k // 2.55k) * 27pF & the final steady state voltage across R26 is ( (19*2.55)/(2.55+15.1)) = 2.745V, which is less than the reference voltage ( which is 3V from TL431 circuit ).,  means fault is not detecting by the hardware. Let me know  if i  am wrong & also explain me the short circuit time setting.

Regards

Nagasahitya.m

  • 0
    TI__Mastermind 18120 points

    Hi Nagasahitya,

    Good catch. The board went through a couple of different adjustments. R25 was initially populated for different drive output voltages. At last we didn't populate R25, and we forgot to put it DNP in the schematic. We will update it. Sorry for the confusion.

  • 0 in reply to Xun
    Intellectual 550 points

    Hiii Xun,

                      Thank you for your reply. I have a one more query related to two level tun off in TIDA-01605. what will be the two level turn off voltage with R13 = 27 ohm . what is the purpose of adding C25 in series with R13 , how its value is decided? Please explain clearly.

  • 0 in reply to naga sahitya
    TI__Mastermind 18120 points

    Hi Nagasahitya,

    This has been descried in detail in the design guide page 10. The gate resistor and R13 creates the voltage divider for the mid-level.

  • 0 in reply to Xun
    Intellectual 550 points

    Hiii Xun,

                    I have seen the detail explanation given in page no.10. But the real confusion is with the waveforms given in page no.11, where it is showing as around 7V. Please clarify the confusion. I have also asked about the requirement of C25= 0.1uF in my previous query, please explain it.

    Regards

    Nagasahitya.m

  • 0 in reply to naga sahitya
    TI__Mastermind 18120 points

    Hi Nagasahitya,

    We initially designed the mid-level voltage to 7V and this was verified via simulation. However during the test afterwards we found that 7V excites too high overshoot therefore we increased the R13. The simulation reflects the concept with initial RC values. 

    At the moment when gate starts discharge, C25 is seen as short circuit, then C25 stabilizes the mid level voltage. Therefore C25 must be much larger than gate capacitance of the MOSFET. 0.1uF is 150 times the value of MOSFET gate capacitance which provides sufficient energy storage.