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UCC256403: Are there any conditions other than "OCP3 threshold" to enter OCP3 operation?

masaki tosu
Prodigy 10 points
Part Number: UCC256403

Figure 1 shows OCP3 operating waveforms. Figure 2 shows OCP3 not working.

The ISNS pin (ch2) in Fig. 1 has an average value of 0.403V per cycle, so it corresponds to "OCP3 threshold min 0.40V".

Figure 2 is also 0.449V, so it should correspond to "OCP3 threshold min 0.40V". However, Figure 2 does not show OCP3 operation.

In addition, the operation to pull out the FB terminal from another circuit is implemented.

fig.1

fig.2

ch1: output voltage ch2: ISNS pin voltage ch3: HO pin voltage ch4: output current

thank you.

  • +1
    TI__Genius 15155 points

    Hi Tosu,

    We have verified with other boards. There is no issue with the OCP fault detection for this controller.

    As per data sheet, OCP3 threshold can be anywhere between 0.4 to 0.46V. 

    So, can you increase the current further and see the OCP3 triggering.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 10 points

    Hi Manikanta,

    Sorry for my lack of explanation.

    Why is Figure 2 not OCP3?

    Since the ISNS voltage in Figure 2 is higher than in Figure 1, we assume that it should OCP3.

    thank you.

    Tosu

  • 0 in reply to masaki tosu
    TI__Genius 15155 points

    Hi Tosu,

    As I mentioned before, OCP3 threshold can be anywhere between 0.4 to 0.46V as per the datasheet.

    Could you increase the output current little further and see OCP3 is getting triggered?

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 10 points

    Hi Manikanta,

    I tried increasing the output current by 10A, but OCP3 does not work.
    Figure 3 shows the waveforms.

    Fig.3


    Compared to Figure 2, the ISNS voltage of ch2 has also increased.
    thank you.

    Tosu

  • 0 in reply to masaki tosu
    TI__Genius 15155 points

    Hi Tosu,

    Could you increase the RISNS value further. See if this improves the situation. Also, could you let me know how you measuring the OCP3 value from your actual ISNS signal.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 10 points

    Hi Manikanta,

    Currently, it is not possible to change the value of RISNS.

    The value of OVC3 is measured by the oscilloscope's measure function to measure the amount of charge on ISNS.
    The range to be measured is the area where the high side is ON and positive.
    By dividing the amount of charge by the time of one cycle, the average value of one cycle is obtained.
    Please let me know if there is a different measurement method.

    Thank you.

    Tosu

  • 0 in reply to masaki tosu
    Prodigy 25 points

    Hello Manikanta,

    May i ask you to help with FA analysis of few samples of Part • UCC256301LLC controller SOIC16 from TEXAS INSTRUMENTS.

    Thank you in advance

    BR,

    Mykhailo

  • 0 in reply to Mykhailo Zubaka
    TI__Genius 15155 points

    Hi Mykhailo,

    The questions were related to UCC256403. Why do you want to send UCC256301 for FA analysis? Could you explain to me more?

    Regards

    Manikanta P

  • 0 in reply to masaki tosu
    TI__Genius 15155 points

    Hi Masaki,

    The measurement method was correct. I would assume that there could be a measurement error (since there is lot of switching noise on the actual signal, Also actual turn on and turn off are difficult to identify for finding average as there is a delay involved ) since we are taking about very tight tolerances. As I mentioned before, we have verified this OCP protection, on several test plat forms. If possible, try to increase the resistance value just to verify the functionality. Let me know what you think.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Prodigy 10 points

    Hi Manikanta,

    got it. Currently, the resistance value of RISNS is 47Ω, how much should I increase it?

    Regarding "OCP3 threshold" sensing, is it detected by the average value of the plus side of the ISNS waveform?

    Or do you include the negative side as well? 

                                               Fig.4

    In Figure 4, ch2 is the ISNS voltage and ch3 is HO.

    The yellow filled range is the positive side, and the red filled range is the negative side.

    thank you.

  • +1 in reply to masaki tosu
    TI__Genius 15155 points

    Please Use the design calculator for finding out this RISNS value.

    For finding the average of ISNS signal, you need to consider both positive and negative sides during HO on.

    Regards

    Manikanta P