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Query -Issue of humming sound coming from motors and Hold /Operating current calculation with 'DRV8834PWP'

Amit Patil32
Prodigy 50 points
Other Parts Discussed in Thread: DRV8834, CSD15380F3

Good evening.

This is regarding TI-Motor Driver 'DRV8834PWP' ,humming sound of motor and  Operating & holding current through it.

We have updated circuit to resolve issue of jerk as per our previous mail communication. 

Please refer attached block diagram for updated motor driver connections with motor and Motor datasheet.

We are operating motors with following general steps :

  1. Enable all motor drivers by making EN pin low
  2. Make DIR Low or High
  3. Select any one motor by A0,A1 & A2
  4. Provide required steps to selected motor
  5. Once operation on 1st motor is done ,select other motor by A0,A1 & A2 ,make DIR=Low/High ,provide steps to selected motor        
  6. Once operations on all motors are completed, Disable all motors drivers by making EN pin High

 

Here we are keeping all motors enabled till operations on all motors get done.

  • Motor Voltgae (VM)=9VDC
  • Itrip set to 180mA/winding 
  • VCC=3.3VDC
  • Operating step frequecy=4.8KHz

 

Observations:

  1. When we enable all motor drivers,we hear humming sound.

If we start operating any  single motor,there is no  hummimg sound coming from that motor,but remaining 5 enabled motors still produce humming sound.

 

  1. We are redesigning motor power supply circuit .For that we have calculated thereotical motor current and measured practical motor current.Refer below table.

Motor Current Calculations

Itrip =180mA/winding   (set current)

Theoretical Calculations

Practical calculations

Description

Max. Current /winding

(with Itrip =180mA/winding)

Max. Current /winding

(with Itrip =180mA/winding)

as per Motor Driver IC datasheet Table 5. Current and Step Directions

Winding A

 

Motor Rated current /Phase

0.180A

0.128A (71% at winding A)

0.152A (Winding A)

0.52A (Winding B)

Motor Rated current /2-Phases

0.360A

0.256A

0.204A

Total Motor current /simulator (6motors)

2.160A@9VDC

1.534A@9VDC

Total current =0.516@9VDC

 

Queries:

  1. How can we remove the humming sound coming from motors?
  2. In our application,at a time one motor is operating and other motors are with holding current flowing through theier windings.Will the value of Hold current and opearing current different?
  3. Total motor current calculated theoretically and practically are not matching as in above table.

Which current should we take for motor power supply design?or Is any parameter missing in theoretical calculations?

  • 0
    TI__Guru** 114905 points

    Hi Amit,

    The attached block diagram and motor specification did not appear. Would you please resend it?

    Amit Patil32 said:

    How can we remove the humming sound coming from motors?

    Do you need the other motors to hold while moving one motor? If not, you could use the nSLEEP or nENBL pin to disable the other motors. This would also reduce your power budget. If you need the motors to hold, you could lower the VREF input to reduce the hold current.

    Amit Patil32 said:

    In our application,at a time one motor is operating and other motors are with holding current flowing through theier windings.Will the value of Hold current and opearing current different?

    The total current in both windings when holding and operating should be approximately the same.

    Amit Patil32 said:

    Total motor current calculated theoretically and practically are not matching as in above table.

    Which current should we take for motor power supply design?or Is any parameter missing in theoretical calculations?

    It is generally best to design for the theoretical maximums. You may be able to reduce your power supply budget if you can take advantage of the nSLEEP  or nENBL pin.

  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Rick,

    Thank you for reply.

    Block diagram & Motor interfacing diagram are attached for your reference.

    Stepper Motor Driver Interface Operating.pdf SH2141-5541.pdf

    We need the other motors to hold while moving one motor .So we can not use nSleep and n Enable.

    Lowering Vref input is OK ,but due to fixed Vref provided ,we cannot change Vref on the fly.

    1. When we enable all motor drivers at a time,we hear humming sound.If we start operating any  single motor,there is no  humming sound coming from that motor,but remaining 5 enabled motors still produce humming sound.

    Query-1: Why do this humming sound coming from motors?Is it because of Hold current only?If i change Vref ,will it reduce/remove this humming sound?

           2.We do agree with you that it is best to design for the theoretical maximums.

    As per Motor Driver IC datasheet Table 5 -Current and Step Directions,It gives therotical maximum as 71% at winding A + 71% at winding B.(refer below table column 3rd).

    Query-2: Shall we consider 71% of Itrip as max theoretical current through single winding for motor power supply Design?

    Motor Current Calculations

    Itrip =180mA/winding   (set current)

    Theoretical Calculations

    Description

    Max. Current /winding

    (with Itrip =180mA/winding)

    Max. Current /winding

    (with Itrip =180mA/winding)

    as per Motor Driver IC datasheet Table 5. Current and Step Directions

    Motor Rated current /Phase

    0.180A

    0.128A (71% at winding A)

    Motor Rated current /2-Phases

    0.360A

    0.256A

    Total Motor current /simulator (6motors)

    2.160A@9VDC

    1.534A@9VDC

    Regards

    Amit Patil

  • 0 in reply to Amit Patil32
    TI__Guru** 114905 points
    Hi Amit,

    Query-1: Why do this humming sound coming from motors? Is it because of Hold current only? If i change Vref ,will it reduce/remove this humming sound?

    The DRV8834 is PWM'ing at slightly different frequencies within the motor. The interaction between the two frequencies can create the humming sound you are hearing. Reducing the VREF can reduce/remove the humming sound. To lower the VREF, a small n-channel FET such as the CSD15380F3 can be used to create a parallel resistance path for holding current.

    Query-2: Shall we consider 71% of Itrip as max theoretical current through single winding for motor power supply Design?

    Since there are tolerances in the resistor, the VREF voltage and the comparator, you might consider increasing the percentage to ~80%. Using Mixed or Fast decay can lower the percentage.