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ADT7470 automatic mode and the PWM is incorrect

I use EVAL-ADT7470EBZ and use Automatic Fan Speed ​​Control Mode the following settings:
TMIN: 25
PWM min: 20
PWM MAX: 100

According to the description of DataSheet, when the temperature reaches Tmin + 20 degrees, the PWM Duty will reach the value set by the PWM Max.

My Tmin is 25 degrees, theoretically when the temperatyre reaches 45 degrees, the PWM will be 100%
However, in reality when temperature reaches 45 degrees, the PWM Duty is only 83%, and when the temperature reaches 51 degrees, than he PWM Duty will be 100%.

Did I set a wrong?

Parents
  • Hi, 
    I used default settings on my board here, except I'm on channel 2 because the fan on Channel 1 in my board is not populated at the moment, and I'm getting 100% PWM on channel 2 when temp 2 is at TMIN+20C. Are you using the heater control function on the software too?

    Regards,
    Karen

  • Hi,

    I edited my response to note I used mostly default settings instead of "same". I had on PWMMIN=50. When I set this to 20% like you, it was also around 80%, in my tests PWMMIN has to be at least 40% for PWM going to get to max when temp is TMIN+20. I'll be checking if I can find how this was characterized before, I suspect it was with the default PWMMIN as well.

    Regards,

    Karen

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  • Hi,

    I edited my response to note I used mostly default settings instead of "same". I had on PWMMIN=50. When I set this to 20% like you, it was also around 80%, in my tests PWMMIN has to be at least 40% for PWM going to get to max when temp is TMIN+20. I'll be checking if I can find how this was characterized before, I suspect it was with the default PWMMIN as well.

    Regards,

    Karen

Children
  • Hi Karen

    Yes, I am using the heater control function on the software too.

    Also, no matter what I set my PWM max value(whether is 100 or 30) the pwm will always rise by 3% with a degree increase in temperature. Which I believe means that the slope are the same no matter the PWM max value is. But this doesn't correlate to the datasheet description where "When the temperature reaches TMIN + 20°C, the fans increase in speed to PWMMAX. ". Is my understanding flawed?