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TMS320F28020: internal temperature AD

Howard Zou
Genius 12365 points
Part Number: TMS320F28020

Hi, my customer wants to use internal AD(channel A5) to sense the temperature and do the internal oscillator compensation.

But the sampled temperature is always about 10+ degree C higher than the temperature set in the oven.

Where exactly does the internal temperature sensor measure?

Is it normal to be 10+ degree C higher?

  • 0
    TI__Guru 60865 points
    Hi Howard,

    The absolute temperature accuracy is not very high; it is typically around +/-10 deg. C. However, this actually doesn't actually affect how well the oscillator is compensated.

    During factory trim/test flow, multiple temperature sensor readings are taken at different temperatures along with the ideal trim for the oscillator at each temperature. A line is then fit to the sensor readings vs trims and stored in OTP (the absolute temperature is not used at all). In this way, as long as the sensor readings are linear and the oscillator trims are linear, then the oscillator will be compensated well.
  • 0 in reply to Devin Cottier
    TI__Genius 12365 points
    Thanks Devin,
    So you mean that if the AD temperature sensor is increasing linearly with the ambient temperature increasing, it means that the sensor is working correctly, right?
    I still would like to know at the design stage, is device junction temperature or the ambient temperature measured when we are using the AD temperature sensor?
  • 0 in reply to Howard Zou
    TI__Guru 60865 points
    Hi Howard,

    Yeah, for the purpose of compensating the oscillator, we just need the temp. sensor to be consistent and linear.

    The on-chip temp sensor measures the device die temperature, not the ambient temperature.