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Original question:

AMC6821: I2C issues with Intelligent Temperature Monitor and PWM Fan Controller

AMC6821: Sometime provides false fan speed while using Auto temperature-fan mode

Narendra Babu
Prodigy 60 points
Part Number: AMC6821

Hi,

We are using the AMC6821 for temperature monitoring.

The mode used is Auto Temperature-Fan mode

The issue we are facing is suddenly the fan speed spikes to a big value like around 5000 even though there is no valid temperature change.

Usually the fan speed will around 2,5, but suddenly some times it will become almost double of this normal speed and automatically decrease again in few seconds.

Please let us know whether this is known issue are any configuration to be corrected so that we will not get false speeds.

Thanks,

Narendra

  • 0
    TI__Guru* 91086 points

    Dear Narendra - 

    Thanks for the post - in this case, to help you further, I think a little more detail is needed from you to assist.

    Which sub-mode of the Auto Temperature Fan control mode are you employing? See page 36 in the datasheet for the definitions of FDRC1 and FDRC0. 

    Then, also please report back what you have set Local and Remote TEMP-FAN control registers, as well as the DCY-Ramp register. 

    It may also be useful if you can capture both the remote and local temperatures when you observe this error. 

  • 0 in reply to Josh Wyatt
    Prodigy 60 points

    Hi Josh,

    Thanks for the quick response.

    Here is the information you requested for further analysis.

    We are having three fans and all three fans are set with identical configurations.

    ~~~~~~~~~~~ FAN 1 information ~~~~~~~~~~~

    Address: 0x18
    Fan Control Mode: Maximum Fast-Speed Calculated
    Speed(current): 2514 or 0x9d2 RPM
    Speed configured: 0 or 0x0 RPM
    Speed minimum limit: 0 or 0x0 RPM
    Speed maximum limit: 0 or 0x0 RPM
    Configuration register 1 start bit: 1
    == Configuration Register 1 data ==
    Hex: 0xfd
    Bin: 11111101
    == Configuration Register 2 data ==
    Hex: 0x3f
    Bin: 00111111
    == Configuration Register 3 data ==
    Hex: 0x83
    Bin: 10000011
    == Configuration Register 4 data ==
    Hex: 0x08
    Bin: 00001000

    == Local Temperature Control Register 0x24 data ==
    Hex: 0x29
    Bin: 00101001

    == Remote Temperature Control Register 0x25 data ==
    Hex: 0xd9
    Bin: 11011001


    ~~~~~~~~~~~ FAN 2 information ~~~~~~~~~~~

    Address: 0x19
    Fan Control Mode: Maximum Fast-Speed Calculated
    Speed(current): 2507 or 0x9cb RPM
    Speed configured: 0 or 0x0 RPM
    Speed minimum limit: 0 or 0x0 RPM
    Speed maximum limit: 0 or 0x0 RPM
    Configuration register 1 start bit: 1
    == Configuration Register 1 data ==
    Hex: 0xfd
    Bin: 11111101
    == Configuration Register 2 data ==
    Hex: 0x3f
    Bin: 00111111
    == Configuration Register 3 data ==
    Hex: 0x83
    Bin: 10000011
    == Configuration Register 4 data ==
    Hex: 0x08
    Bin: 00001000

    == Local Temperature Control Register 0x24 data ==
    Hex: 0x29
    Bin: 00101001

    == Remote Temperature Control Register 0x25 data ==
    Hex: 0xd9
    Bin: 11011001


    ~~~~~~~~~~~ FAN 3 information ~~~~~~~~~~~

    Address: 0x4C
    Fan Control Mode: Maximum Fast-Speed Calculated
    Speed(current): 2713 or 0xa99 RPM
    Speed configured: 0 or 0x0 RPM
    Speed minimum limit: 0 or 0x0 RPM
    Speed maximum limit: 0 or 0x0 RPM
    Configuration register 1 start bit: 1
    == Configuration Register 1 data ==
    Hex: 0xfd
    Bin: 11111101
    == Configuration Register 2 data ==
    Hex: 0x3f
    Bin: 00111111
    == Configuration Register 3 data ==
    Hex: 0x83
    Bin: 10000011
    == Configuration Register 4 data ==
    Hex: 0x08
    Bin: 00001000

    == Local Temperature Control Register 0x24 data ==
    Hex: 0x29
    Bin: 00101001

    == Remote Temperature Control Register 0x25 data ==
    Hex: 0xd9
    Bin: 11011001

    DCY-Ramp register is default value which is 0x52.

    Local and remote temperatures(in degree Celsius) when RPM spikes up are as below.
    One more observation is Fan3 is not exhibiting this behavior.

    FAN1 speed : 4971 RPM
    Fan1 Local Temperature : 28.625
    Fan1 Remote Temperature: 28.125
    FAN1 speed : 4971 RPM
    Fan1 Local Temperature : 28.750
    Fan1 Remote Temperature: 28.250
    FAN1 speed : 4991 RPM
    Fan1 Local Temperature : 28.500
    Fan1 Remote Temperature: 28.000
    FAN1 speed : 5004 RPM
    Fan1 Local Temperature : 28.625
    Fan1 Remote Temperature: 28.125
    FAN2 speed : 4966 RPM
    Fan2 Local Temperature : 28.750
    Fan2 Remote Temperature: 28.000
    FAN1 speed : 5004 RPM
    Fan1 Local Temperature : 28.500
    Fan1 Remote Temperature: 28.000
    FAN2 speed : 4983 RPM
    Fan2 Local Temperature : 28.500
    Fan2 Remote Temperature: 27.875
    FAN2 speed : 4983 RPM
    Fan2 Local Temperature : 28.500
    Fan2 Remote Temperature: 27.875
    FAN1 speed : 4958 RPM
    Fan1 Local Temperature : 28.750
    Fan1 Remote Temperature: 28.000
    FAN1 speed : 4966 RPM
    Fan1 Local Temperature : 28.500
    Fan1 Remote Temperature: 28.125
    FAN2 speed : 4966 RPM
    Fan2 Local Temperature : 28.625
    Fan2 Remote Temperature: 28.000
    FAN1 speed : 4971 RPM
    Fan1 Local Temperature : 28.500
    Fan1 Remote Temperature: 28.125
    FAN1 speed : 4971 RPM
    Fan1 Local Temperature : 28.500
    Fan1 Remote Temperature: 28.000

    Please help us to resolve this soon.

    Thanks,

    Narendra

  • 0 in reply to Narendra Babu
    TI__Mastermind 35895 points

    Hi Narendra,

    The temperature is updating every 62.5ms (see Conversion Time spec.) It is possible you are not sampling fast enough to see remote temperature noise. We often see noise induced on remote temperature channels for all of our products due to the low current levels necessary.

    Do you see the same fan speed spikes with Software DCY or RPM modes (FDRC = 0 or 1)?

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 60 points

    Hi Ren,

    We are in Auto Temperature Fan control mode and read the fan speeds & temperatures at the rate of  1 second only but we still these spikes.

    One more observation is, we have three fan control chips and only two of them exhibiting this behavior and the third one is not giving any spikes in fan speeds.

    The configuration is same for all the three fans.

    What could be the reason for these spikes only in 2 chips but not on the third chip.

    Thanks,

    Narendra

  • 0 in reply to Narendra Babu
    TI__Mastermind 35895 points

    Hi Narendra,

    Please test in Software DCY or RPM modes.

    Please also let us know what is tied to your THERM pin. If this pin floats, it could trigger fan activity randomly.

    Noise on the remote temperature channel would be location specific. It would be caused by nearby components. When the noise makes the remote temperature appear high, the fan will speed up accordingly. You are not sampling fast enough to see all of the temperature measurements and could miss an intermittent high temperature reading.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 60 points

    Hi Ren,

    We read the temperatures as you mentioned for every 62.5  milliseconds and saw that there is no spike in temperature values.

    But still we saw spikes in fan speeds. Regarding THERM pin , it is pulled up but not floated.

    Please let us know if there is any other reasons which can cause spikes in fan speed.

    Thanks,

    Narendra

  • 0 in reply to Narendra Babu
    TI__Mastermind 35895 points

    If you captured all of the reported fan speeds, then the AMC6821 is not commanding the fan to speed up. Some other noise or activity on the fan or circuitry connected to PWM is causing the perceived speed change. 

    thanks,

    ren