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TMAG5111: Query about Direction Sensing using 2D Latch

Neet
Intellectual 532 points
Part Number: TMAG5111
Other Parts Discussed in Thread: TSD05, TMAG5110

Tool/software:

Hello E2E Community,

We are planning to use the TMAG5111 2D Hall Effect latch for our next project, which requires separate outputs for speed and direction sensing.

I have a specific query regarding the detection of direction after a system reset. Here's the scenario:

  1. The machine starts from zero, and we allow an initial stabilization time of 1 second.
  2. The sensors record rotational speed and direction.
  3. The system is then switched off and restarted in the reverse direction.

In this case, while the speed detection is straightforward, I want to confirm the behavior of the direction output. Specifically:

  • For clockwise rotation, will the direction output consistently be high?
  • For counter-clockwise rotation, will the direction output consistently be low?

Is it correct to assume that, regardless of the system's configuration and state, we can map the direction output as high for one direction and low for the other?

Also, do we need to install ESD diode close to the sensor? We plan to minimize the component count near the sensor by using only decoupling MLCC of 0,1uF - let us know if we can simply add 27Ohm pulse proof resistors on OUT1 & OUT2 pins for some safety while having a TVS diode installed on the MCU side (TSD05)? Or do we also need to install the TVS diodes near the Sensors? Our system works on 5V DC & the length of the wires shall be no more than 3m from the host MCU.

Your insights would be greatly appreciated.

  • 0
    TI__Mastermind 23695 points

    Hey Neet,

    The TMAG5111 uses the same circuitry as the TMAG5110.  If you look at figure 8-3 in the datasheet, you can observe for the TMAG5110 that there are two sensors monitoring the flux in two perpendicular axes (90° out off phase).  Based on the order of rising and falling edges with these sensors, that is how the direction is determined.  So as long as the device is powered and you are spinning in the same direction, the direction signal should be constant.  If you power off, I don’t think the last state is remembered.  I will check with my team on that. 

    Orientation will have influence on how the field looks to the device.  For instance a north pole of the magnet has flux oriented out of the magnet.  If you look at one sensor at a fixed point  above this magnet pole, the device hall sensor sensing in the z-axis will read a negative value if the package top faces the north pole and will read a positive value if the package bottom faces the north pole.

    Most TI devices have some level ESD protection integrated into the chip.  Unless you are expecting conditions that exceed the limits stated in our ESD ratings section, I don’t think you need an ESD nearby.  However, having the decoupling capacitor near to the device supply pin and ground pin is highly recommended.  Are you using 270ohm resistors as a pull-up to the supply of 5V.  If so I think those value might be a little small and may negative impact the output high value.

  • 0 in reply to Patrick Simmons
    Intellectual 532 points

    Hello Patrick,

    1) Do let us know about the Direction output signal on the TMAG5111 - how does it behave during active state & then after power off state

    2) We are planning to use a 27-Ohm resistor in series to act as current limiting resistor in case of EOS/ESD event - for Pull up we are using 4.7k on the MCU side

  • 0 in reply to Neet
    TI__Mastermind 23695 points

    Hello Neet,

    Thanks for clarifying that, I have forwarded your questions to one of our design engineers, will let you know when I have an update from him.

  • 0 in reply to Patrick Simmons
    TI__Mastermind 23695 points

    Hello Neet,

    As this is one of our older parts, the people that worked on it are no longer here.  So I need to dig a little deeper on the issue and potentially run some tests to determine the power back on behavior.

    As for the ESD event, can you comment on if there is a standard you are trying to achieve or perhaps what the ESD characteristic you are designing for looks like?

  • 0 in reply to Patrick Simmons
    TI__Mastermind 23695 points

    Hey Neet,

    I did some tests on a single TMAG5111A2AQDBVR with a rotating diametric magnet and found that often the prior direction was re-asserted upon power on.  However, not always though.  It seems that where the pole boundaries are relative to the device has some impact on the direction outputted when powering up.

  • 0 in reply to Patrick Simmons
    Intellectual 532 points

    Hey ,

    Thank you for the update. So if I understand it properly - for any given use case - where the prior direction needs to be stored - if we store the direction output (which could be HIGH or LOW for the last known direction) after a power on - assuming the rotor shaft to have started from the same instance it stopped, we cannot relay on the direction output bit of the TMAG5111 device, right?

  • 0 in reply to Neet
    TI__Mastermind 23695 points

    Hello Neet,

    Yes the TMAG5111 does not have memory that stores the last direction prior to power-off, and per the tests I performed the direction output may not be the same when the device powers back on, even though the magnetic field source has not moved.