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TMAG5115: RC Filter on remote end on the Hall Effect Sensor

Neet
Intellectual 622 points
Part Number: TMAG5115
Other Parts Discussed in Thread: ESDS312, TMAG5213

Tool/software:

Hello E2E Community,

We are planning to use the low-jitter TMAG5115 Sensor for our Speed sensing use case where we plan to measure 2 pulses per revolution to synchronize our accelerometer data with the shaft speed for TSA ie Time Synchronous Averaging.

I would like to confirm from the TMAG Product Team to help us with feedback on some design decisions:

  1. To minimize the noise glitches on the MCU GPIO end - we are installing a RC based Low Pass Filter with R=1kOhm & C=0.1uF
  2. Install ESDS312 on the Vcc & Vout to the GND wire of the TMAG5115 for ESD protection of the sensor pins

Let us know the impact of RC filter on the Jitter performance if any - the maximum speed we would be measuring shall be 60-90Hz.

  • 0
    TI__Mastermind 23045 points

    Hello Neet,

    Thanks for posting to the sensors forum! Thank you for considering our products for you design.

    The RC filter is great for trying to minimize any noise that may couple to your GPIO signal. As far as the LP filter affecting jitter on your measurement this should not have much of an impact. Jitter is impacted by the slew of the magnetic field so in order to have the best jitter possible for your system, the most crucial item to consider would be the sensor to magnet placement. The higher the magnetic slew is the smaller your jitter is expected to be and the for a smaller magnetic slew rate the higher your jitter is expected to be. This is why the jitter is specified as a value dependent on your magnetic field strength and the shape of the magnetic field on the data sheet (I included a capture of the datasheet below). 

    So while you may not be able to control the shape of your magnetic field in your application but you may certainly control the strength of the magnetic field. As far as any effect caused by the filter the main item to consider would be any phase shift caused by the filter.

    Please let me know if there are any other questions I may be able to help out with!

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Intellectual 622 points

    Hello Issac,

    Thank you for detailed response, I appreciate your suggestion.

    Any recommendations for the filter sizing?

    1. R: 1kOhm & C: 100nF
    2. R: 10kOhm & C: 10nF
    3. R: 100kOhm & C: 1nF

    Let me know which RC Filter configuration is better suited for the TMAG5115 series sensors - higher resistance vs higher capacitor.

    Also is the jitter performance of the TMAG5213 very bad (ie much higher than 5us?) when compared to the TMAG5115?

  • 0 in reply to Neet
    TI__Mastermind 23045 points

    Hello Neet,

    My recommendation would be to first identify what value of resistor you could use for your system, since the resistor is also used as the pullup for the open drain then it is recommended to identify what range of values you can use first and choose something in the middle of the range. Once the resistor has been decided you can consider the capacitance values in order to achieve your LP filter. To calculate the resistors range you would need to use your operating voltage range (min/max), this will help you determine a range of pullup resistors.

    e.g. Vs_max/15mA < R < Vs_min/100uA

    The jitter performance of the TMAG5213 would be worse than the TMAG5115, I think it would be almost 2-3 times as worse.

    Best,

    Isaac