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Original question:

UC2625-EP: UC2625-EP Application

UC2625-EP: Transitions per rotation, computation, etc.

ArTzy
Genius 17625 points
Part Number: UC2625-EP

Hi Experts,

Asking assistance and clarification on these queries:

In the example from the link above, they're stating that 16krpm Mech equals 62.5uS per rotation. How is this value calculated?

I initially thought it was Mrpm/60 = Mrps, 1/Mrps = Mspr and then Mspr/1E-6 = Muspr. What I'm seeing in the response is that 1/16krpm gives 62.5uS per rotation which is incorrect is 62.5 uM per rotation because there wasn't a conversion.

In this response it's also stating that the RPM can be divided by 5 to get the dead time, can you explain this to me?

Also, as highlighted above, what really means by "transition"? As I understand it, it refers to the steps/position of rotor to complete the revolution, correct? Or, are the transitions related to the Tachometer? The Tachometer on this chip triggers whenever there's a change in state for the Hall effect sensors.

In the current system of my customer that is 6 because there are only 3 hall effect sensors, but in the Datasheet it mentions there could be 6 transitions or 12 transitions, which deters me from thinking it's related to the tachometer.

Hope to explain these queries to me.

Thank you very much.

Regards,
Archie A.

PN: UC1625

  • 0
    TI__Mastermind 26046 points

    Hi Archie,

    I am reviewing this today and will get you a response.

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Mastermind 26046 points

    Hi Archie,

    I have not had time to finalize reviewing it, please give me some more time tomorrow to come up with a reply. 

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Genius 17625 points

    Hello Aaron,

    Thank you for your response.

    Looking forward for your updates.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 18981 points

    Hi Archie, 

    we'll take a closer look at this next week. apologies for the delay 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    TI__Genius 17625 points

    Hello Andrew,

    Thanks.

    Customer is looking confirmation and asking an update.

    Let us know if any further information you need on this query to proceed.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 18981 points

    Hi Archie,

    Our team may need a few more days to investigate this but will aim to get you a response by EoD Wednesday. 

    A bit of context: this is a very old device that does not have support from the original team that developed it, so we'll need more time than usual to investigate the datasheet descriptions and clarify device behavior 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    TI__Mastermind 26046 points

    Hi Archie,

    ArTzy said:

    In the example from the link above, they're stating that 16krpm Mech equals 62.5uS per rotation. How is this value calculated?

    I initially thought it was Mrpm/60 = Mrps, 1/Mrps = Mspr and then Mspr/1E-6 = Muspr. What I'm seeing in the response is that 1/16krpm gives 62.5uS per rotation which is incorrect is 62.5 uM per rotation because there wasn't a conversion.

    My calculation is:

    16000RPM = 16000 rotations/60 seconds = 266.67 rot/sec =  3.75ms/rotation. I think their calculation is wrong. 

    ArTzy said:

    In this response it's also stating that the RPM can be divided by 5 to get the dead time, can you explain this to me?

    This calculation is bizarre. The last two sentences indirectly state that the dead time will be 1-2 CLK periods from the RC oscillator clock. I would just assume dead time time worst case will be 2 divided by the RC clock frequency.

    ArTzy said:

    Also, as highlighted above, what really means by "transition"? As I understand it, it refers to the steps/position of rotor to complete the revolution, correct? Or, are the transitions related to the Tachometer? The Tachometer on this chip triggers whenever there's a change in state for the Hall effect sensors.

    In the current system of my customer that is 6 because there are only 3 hall effect sensors, but in the Datasheet it mentions there could be 6 transitions or 12 transitions, which deters me from thinking it's related to the tachometer.

    The tachometer triggers when there's a rising or falling edge, so this is likely the "transition" the datasheet is referring to. If there are 3 hall sensors, then there is 6 total transitions for a DIR direction state.

    My guesses for the 12 total transitions could be:

    1) If the DIR direction state is the opposite and this the motor spins in the opposite state, then this might be the other 6 transition making 12 total transitions in the motor operation, similar to Table 2:

    2) If the Hall sensors also placed 60 electrical degrees apart, then this could be 12 total transitions. 

    Thanks,
    Aaron