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LM63: questions

Allan Fan
Expert 7090 points
Part Number: LM63

Hi Expert,

Customer is looking for fan PWM controller with fan speed monitor. We are proposing LM63 and have some questions. 

1.  can it control fan speed from SMBus directly instead of reading from remote diode?

2. since they already have many thermal sensors in the system, can they don't use remote diode connected to the D+/D-? how should we connect D+/D- if it's not used? 

3. what's the purpose and design rules for R55, R56, R57 in the EVM circuit?

4. how does "PWM value actual=28" in the example came from?

5. RPM

A. from the FAN spec, 2 pulses equal to 1 revolution. Does that corresponding our datasheet formula (2) "f"=1?

B. if Fan spec and our chip definition is different, how to convert the formula?

customer FAN spec:

LM63:

Thanks,

Allan

  • 0
    TI__Expert 6820 points

    Allan,

    Below is my feedback

    Allan Fan said:
    1.  can it control fan speed from SMBus directly instead of reading from remote diode?

    Without a remote connected to the D+/- pins the PWM will go to 100% duty cycle.  If you have a remote connected you can use the manual control mode to control the PWM output.

    Allan Fan said:
    2. since they already have many thermal sensors in the system, can they don't use remote diode connected to the D+/D-? how should we connect D+/D- if it's not used? 

    No, they cannot because PWM will go to 100%.

    Allan Fan said:
    3. what's the purpose and design rules for R55, R56, R57 in the EVM circuit?

    This is a resistor totem pole to step down the voltage that powers the fan to stay within out Abs max voltage range.  

    Allan Fan said:
    4. how does "PWM value actual=28" in the example came from?

    The number 28 is just an arbitrary number to give an example.  24 is an arbitrary number chosen for the PWM frequency and 28 is an arbitrary number chosen for the PWM duty cycle.  

    Allan Fan said:

    5. RPM

    A. from the FAN spec, 2 pulses equal to 1 revolution. Does that corresponding our datasheet formula (2) "f"=1?

    B. if Fan spec and our chip definition is different, how to convert the formula?

    Yes, 2 pulse fan is 2 pulse per revolution which is f=1.  

    Thanks,

    David

  • 0 in reply to David Vaseliou
    Prodigy 20 points

    HI Expert

    Thank you for solving the hardware design problem,
    I have a question about register settings. Before using the fan control IC in the data sheet, four registers must be set. Please give four register recommendations based on fan specifications.
    • FAN operationg frequency: 25KHz

     

    Q1: Is the value of register 4A set to 0x20?

    Q2:The product will use three target duty cycles (60%, 70%, 80%). But I don’t know the setting rules in register 4B? Please give formula.

    Q3: Is the value of register 4D set to 0x7?

    Q4: The product will use three target duty cycles (60%, 70%, 80%). But I don’t know the setting rules in register 4C? Please give formula.

    BRs
    Chaochen

  • 0 in reply to Chaochen Huang
    TI__Expert 6820 points

    Hi Chaochen,

    Your picture did not upload correctly.  Please try attaching picture again.  Below is my feedback based off the other information.  

    Chaochen Huang said:
    Q1: Is the value of register 4A set to 0x20?

    This depends on how you would like to run the fan.  Based on 25kHz and if you want to use manual control and PWM output pin be 0 V for fan off.  0x20 is correct setting.  

    Chaochen Huang said:
    Q2:The product will use three target duty cycles (60%, 70%, 80%). But I don’t know the setting rules in register 4B? Please give formula.

    This registered is for spin up settings and is dependent on how you would like to start your fan from a full stop.  

    Chaochen Huang said:
    Q3: Is the value of register 4D set to 0x7?

    Register 0x4D = 0x07 would be 25.71kHz when set to 360kHz as shown in the 6th column of the table in the application notes section of the datasheet.

    Chaochen Huang said:
    Q4: The product will use three target duty cycles (60%, 70%, 80%). But I don’t know the setting rules in register 4C? Please give formula.

    Please use equation 1 in the application notes section of the datasheet.  Register 0x4C = 

    0x08 (~57.14 %)

    0x0A (~71.42 %)

    0x0B (~78.57 %)

    Thanks,

    David