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TMAG5170-Q1: The temperature dependence of TMAG5170-Q1

meran_ruru
Prodigy 60 points
Part Number: TMAG5170-Q1
Other Parts Discussed in Thread: TMAG5170,

Hi team.

According to Data Sheets , This sensor has temperature dependence like below.

For example, offset value is 0.15mT.
When ambient temperature is going to be 120° from 20°, offset value will drift -0.2mT ( drift value =  -0.002mT/° × ( 120 - 20 ) )
In data sheets, this value is described only typical value. So, could you tell me max drift value if you know it ?
Also, is there anything else the temperature dependence of  this sensor except offset and gain error ?

Regards

  • 0
    TI__Mastermind 21020 points

    Thank you for reaching out with your question.  TMAG5170 is currently in an advance release stage, and is still under final characterization.  As a result, we do not yet have the typical temperature plots for this device published. Unfortunately, until the datasheet is updated with more details we cannot share any unpublished characterization results.  This means we should consider our estimations from the typical case information as available.  

    Your evaluation for the device performance at 140 °C is correct, at -2 µT/°C we would expect a typical change of about -0.2 mT.  

    It is not uncommon to see some minor change in Icc as temperature drifts in Hall effect sensors as well. I would anticipate seeing a small increase in Icc at 140 °C, but again any estimation here is dependent on unpublished data.

    One thing worth noting on TMAG5170 is that the device also has a programmable temperature compensation feature.  Magnets will lose strength as they heat, and so a positive temperature compensation for device sensitivity will help to counter this effect.  TMAG5170 has three options 0.0 %/°C , 0.12%/°C, and 0.2%/°C.

    Thanks,

    Scott Bryson

  • 0 in reply to Scott Bryson
    Prodigy 60 points

    Scott Bryson

    Thank you for your answering.
    So, I think that if ambient temperture changed,measurement error of magnetic flux densitiy arised like below.

    [ at 20°C ]
    measurement result = ( true value[mT] ± Offset[mT] ± RMS magnetic noise[mT] ) × Sensitivity error [%] × Sensitivity Linearity error[%] ± Quantization error

    [ at 120°C ]
    measurement result = ( true value[mT] ± Offset[mT] + Offset drift[mT] × (120 -20 ) ± RMS magnetic noise[mT] ) × Sensitivity error [%] × Sensitivity Linearity error[%] ± Quantization error

    For example, If Sensor setting is like below,mesurement result as follows.

    [Sensor Settings]
    CONV_AVG = x32
    Measurement_CH = Zch
    Z_RANGE = ±50mT

    [True magnetic flux densitiy]
    20.00[mT] at 20°C
    18.34[mT] at 120°C

    [Measurument Result at 20°C ]
    measurement result = ( 20[mT] ± 0.15[mT] ± 0.064×6(=6sigma)[mT] ) × (100 ±1.1)[%] × (100 ±0.05)[%] ± 1/654[mT]

    So, TMAG5170-Q1 may measure magnetic flux densitiy at 20°C
    =  19.24[mT] (min) ~ 20.77[mT] (max)

    [Measurument Result at 120°C ]
    measurement result = ( 18.34[mT] ± 0.15[mT] + (-0.002[mT] × (120-20) ± 0.064×6(=6sigma)[mT] ) × (100 ±1.1)[%] × (100 ±0.05)[%] ± 1/654[mT]

    So, TMAG5170-Q1 may measure magnetic flux densitiy at 120°C
    =  18.89[mT] (min) ~ 20.77[mT] (max)

    In this way, I think that measurement result was calculated as above.
    Are they correct calculates?

    I'm sorry to trouble you ,but please reply regarding this matter.

    Thank you

  • 0 in reply to meran_ruru
    TI__Mastermind 21020 points

    I noticed a few items reviewing your summary.  

    • At 120C you indicate an actual magnetic field of 18.34 mT.  This suggests a temperature drift for this magnet of about -0.08 %/C.  Typically, on average, NdFeB magnets will weaken at -0.12 %/C.  The expected field at 120 C would normally be approximated at 17.6 mT.
    • Sensitivity Linearity Error is the maximum deviation from the best fit line.  This is more accurately be represented additively as an offset
    • 6 sigma is a very conservative estimate for a typical measurement, but we can use it for a worst case scenario
    • The +/-100 mT range has an actual full scale input range of 200 mT.  We should use this for the linearity error calculation and when calculating quantization error.

    To approximate an actual measurement, we might use the following equation:

    Result = Floor ( LSB size * ( (Input Field +/- Noise * Sigma) * (1 +/- Sensitivity Error + Temp Compensation * (Actual Temp - 20C) ) +/- Offset - Offset Drift * (Actual Temp - 20C) ) / Full Scale Output * Output Range

    For your example if we assume the 18.34 mT input is correct, I get the approximate ranges below. 

    20 C:

    ( 326 LSB/mT * (20 mT +/- 0.064 mT*6 sigma ) * (1+/-0.011 ) +/- 0.15 mT +/- .0005*200 mT ) / 65536 LSB * 200 mT = 19.05 mT ~ 20.75 mT

    120 C:

    (326 LSB/mT * (18.34 mT +/- 0.064 mT*6 sigma ) * (1+/-0.011 + 0.0012 * 100 C ) +/- 0.15 mT +/- .0005 * 200 mT - 0.002 mT/C *100 C ) /  65536 LSB * 200 mT =  19.36 mT ~ 21.12 mT