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AMC6821: AMC6821 - Fan Oscillation

Kjetil Oftedal
Intellectual 260 points
Part Number: AMC6821


I have a issue with AMC6821 running in Software-RPM mode.

If the requested speed is set so low that the connected fan stops the AMC6821 will enter some sort of internal condition causing the connected fan to oscillate. Even after the speed is changed to a higher speed that the fan should be able to run normally at.

Readouts with ~one second in between:
Actual speed  :  0x37 RPM:   5102
Actual speed  :  0x25 RPM:   4444
Actual speed  :  0x3d RPM:   5494
Actual speed  :  0x68 RPM:   8310
Actual speed  :  0x4d RPM:   6543
Actual speed  :  0x35 RPM:   4971

The requested speed by the CPU was here 0x55.

A normally running fan gives:

Actual speed  :  0x56 RPM:   7134
Actual speed  :  0x57 RPM:   7194
Actual speed  :  0x59 RPM:   7263

Is there any way of resetting the internal regulator without resetting the entire chip?

  • 0
    TI__Expert 6820 points

    Hi Kjetil,

    I am looking into seeing if there is a way to reset just the internal regulator.  In the meantime can you send me your register settings?

    Thanks,

  • 0 in reply to David Vaseliou
    Intellectual 260 points

    Registers:

    Config Reg 1 = 0x21

    Config Reg 2 = 0x07

    Config Reg 3 = 0x03

    Config Reg 4 = 0xA8

    Fan Charact. = 0x20

    DCY-RAMP     = 0x12

    Fan Tach Limit Low  = 0x30 , 0x75

    Fan Tach Limit High = 0xFF, 0xFF

    Full dump of the first 64 registers:

    -------------------------------------------------------
     0000: 21 07 00 00 A8 00 C5 00 25 03 1B 26 00 00 00 00 |
     0010: 30 75 FF FF 3C 00 46 00 50 00 64 50 00 69 37 03 |
     0020: 9D 55 5A 12 41 61 00 00 00 00 00 00 00 00 00 00 |
     0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 21 49 03 |
    -------------------------------------------------------

  • 0 in reply to Kjetil Oftedal
    TI__Expert 6820 points

    Hi Kjetil,

    When the fan starts oscillating try changing to DCY mode and set the fan to a stable higher speed and then return to the Software-RPM mode to regulate the fan speed. 

    Thanks,