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TCAN1145-Q1: What is POR?

Masatoshi Oguri
Expert 4780 points
Part Number: TCAN1145-Q1

Hello,

What is POR? I guess it stands for Power On Reset and sometimes it is a voltage level also called as “POR level”, which is probably the same as VSUP(PU)R/VSUP(PU)F. However, I cannot find any meaningful difference from “Power Up” and UVSUP. I think all those 3 are effectively the same. Why do you treat them as different events? What difference should be kept in mind when the device is used?

In the figures 10-8 through 10, the device goes into standby mode anyway. No effective difference.

In “10.4.7.6.1 UVSUP, UVCC” the explanation is “If VSUP decreases more, the TCAN114x-Q1 shuts everything down as the POR level has been reach and when VSUP returns, the device comes up as if it is the initial power on.”. But the device is power off under UVSUP anyway.

In “11.2.2.1 Brownout”, Brownout is defined as “when VSUP is ≤ UVSUP but > POR state”. But what is meaningful in the figure is just ≤ UVSUP. POR state is not necessary here and effectively the same as UVSUP.

I tried hard to figure out what the difference is to find everything suggests they are effectively the same.

Thank you.

Regards,

Oguri (TIJ automotive FAE)

  • 0
    TI__Guru 74262 points

    Oguri-san,

    The biggest difference is the device's register contents. If a Undervoltage on VSUP occurs, the device will still retain it's register configuration, but just go into a fault state. If a POR event occurs, the register contents will not be retained and the device has to be reconfigured. Also, UVSUP will place the device into Standby mode automatically if the voltage stays above the POR threshold, but if the VSUP voltage is below the POR threshold, it will be in an off state.

    Regards,

    Eric Hackett

  • 0 in reply to Eric Hackett
    TI__Expert 4780 points

    Thank you for the feedback.

    So, it seems the datasheet requires correction. In the Table 10-8 when VSUP is <UVSUP, the device is to be Power off. But it actually should be Standby, as the 1st line of the 10.4.7.6.1 explains.

    This wrong information as well as undefined term of POR make the datasheet highly confusing. If you actually make a correction I would like you to first define the POR, then provide descriptions independently for POR, UVSUP, UVCC, UVIO. Explaining about UVSUP and VCC in the same section as well as the hidden POR makes it very difficult to understand (it seems also the writer was confused). And I would like you to remove the meaningless discussion about Brownout. It is just UVSUP event.

    Please confirm one thing, is POR level the same as VSUP(PU)R/F?

    Thank you.

    Regards,

  • 0 in reply to Masatoshi Oguri
    TI__Expert 4780 points

    Hi Eric,

    Please confirm one thing, is POR level the same as VSUP(PU)R/F?

    Thanks you.

    Regards,

    Oguri

  • 0 in reply to Masatoshi Oguri
    TI__Mastermind 26806 points

    Oguri-san,

    I apologize for any confusion. The information you cited is not incorrect.

    As Eric mentioned in his response above, these are different thresholds.

    When a UVSUP event occurs, the device enters Standby mode as mentioned in 10.4.7.6.1 and Figure 10-8/10-9/10-10 (State Diagrams). This is also the entire reason that the Brownout section (11.2.2.1) exists, since this condition occurs.

    When the supply is below the UVSUP threshold, the device is effectively off. This is what you see in Table 10-8 as you included above. When the UVSUP event ends, the device will be in Standby mode, even though a POR has not occurred.

    Standby mode is the result of an undervoltage event, which is usually short.

    When UVSUP occurs, you will see interrupt 8'h52[4] (INT_2[UVSUP]) high. Other registers will retain their original contents.

    When POR occurs, you will see interrupt 8'h52[6] (INT_2[PWRON]) high. Other registers will be reset.

    Hopefully this helps clarify things.

    Best,

    Danny

  • 0 in reply to Danny Bacic
    TI__Expert 4780 points

    Hi Danny,

    Thank you for the comment. I see what would happen in POR and UVSUP events. But I still can not know when POR to happen, because there is no clear definition of POR level. Instead there are similar parameters of VSUP(PU)R and VSUP(PU)F in the EC table. What I would like you to do is confirming if these parameters are the same as POR level. Is VSUP(PU)R/F the same as POR level?

    Regards,

    Oguri

  • +1 in reply to Masatoshi Oguri
    TI__Guru 74262 points

    Oguri-san,

    The VVSUP(PU)R/F are labeled as Supply on thresholds, which are in fact the Power on voltage of the device, thus the POR event happens at these thresholds. I understand the confusion, and we can look into addressing this in a datasheet update.

    Regards,

    Eric Hackett