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Original question:

LM63: questions

LM63: Read FAN speed accuracy

Huang chaochen
Prodigy 30 points
Part Number: LM63


Hello,

On the production line, we checked the characteristics of the FAN components. The definition of this standard is the same as the FAN specification which is 10% at maximum RPM. But it has several boards with more than 10%. We think we should consider the tolerance of LM63 to read RPM. Can you share what is the tolerance range?

BRs

Chaochen

  • 0
    TI__Guru* 91206 points

    Dear Chaochen - 

    Thanks for the post and welcome to E2E!

    The tolerance of the PWM output should be +/-10%. What are you measuring in your application and if you can share your schematic along with your settings and conditions of measurement, that would be most helpful. 

  • 0 in reply to Josh Wyatt
    Prodigy 30 points

    Follow you answer, It mean the RPM criterion shall be 20%(FAN tolerance+ PWM tolerance), is correct?

    But test RPM set to maximum mode, The PWM signal output is 100% duty cycle. I can see stable DC level without duty cycle on the oscilloscope. Is it mean no need consider tolerance value at PWM signal?

     information as below.

    1. The register of FAN enable setting as below 

    0x4a 0x20
    0x4b 0x20
    0x4d 0x07
    0x4c 0x0e (MAX FAN rpm)

    3. Schematic 

  • 0 in reply to Huang chaochen
    Prodigy 30 points

    Hello Josh,

    Urgent question for supply shortage.

    The circuit purpose is for control FAN speed and read RPM value only. There is no temperature function needed. Is it possible to use LM63D replace LM63C? 

     

    Chaochen

  • 0 in reply to Huang chaochen
    TI__Guru* 91206 points

    Dear Chaochen - 

    Yes, these parts are electrically connected in the same manner, so you could substitute.  

    Regarding your schematic - the I2C pullup resistors are weak (R131 and R132, set for 10k) would recommend you calculate the correct pullup value needed and I would not recommend installing buffer resistors on I2C line (R129 and R130) unless they are truly needed (usually they are not needed)