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LM5060: High frequency oscillation at output

Intellectual 360 points

Replies: 8

Views: 135

Part Number: LM5060

Hi 

I am using a LM5060 to drive 2 200W brushless DC motor in a automotive robot, but there is high oscillation appear at the output.

Usually the oscillation happens when the robot stop from moving. I wonder what may cause such thing happen?

This oscillation affect the RS485 line of the motor and cause it hang up.

Since the motor has 6000uF capacitance in total, I use the driver to control the inrush current.

The P-MOSFET is to block the reverse current flow if the robot is moved by force manually when the robot power off.

C13 is not installed component.

I tried to removed the P-MOSFET part, but the oscillation still happen.

Yellow is the current of one motor

Green is the voltage of the motor

Blue connected to nothing, oscilloscope is internal grounded. (and the ratio was wrong, please x10 the amplitude)

Usually the oscillation happens when the robot stop from moving, but sometime it happen while moving. 

Also, if I lift up the robot and left the motor run in no load, it seems that oscillation does not happen.

If anyone could help, I would be really appreciate. 

Thanks

  • upload photo!

    https://imgur.com/a/AwvQhqc

    Thanks

  • Guru 53675 points

    In reply to Hoi Keung TANG:

    Hi Tang,

    Thanks for reaching out!

    The characteristics of BLDC motor varies a lot from make to make. Can you please get test waveforms when the BLDC motor is powered from direct DC supply similar to Figure-1 to Figure-5 in the app note http://www.ti.com/lit/an/slva683a/slva683a.pdf. This helps to understand the motor characteristics and to check how the LM5060 is interacting.

    In the second case with LM5060 circuit in the setup, provide test waveform of Vin, Vout, GATE, input current (in a single scope shot) during startup, running, stop scenarios.

    Best Regards, Rakesh

    --------------------------------------------------------------------------------------------------------

    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

  • In reply to Rakesh:

    Hi Rakesh

    Thanks for replying!

    Here is the waveform during startup that captured long time ago.

    Yellow is input voltage, green is motor voltage, red is input current.

    https://imgur.com/a/AzUTVSg

    It is difficult to get the waveform of oscillation because it sometimes may not happen at all.

    Thanks

  • Guru 53675 points

    In reply to Hoi Keung TANG:

    Hi Tang,

    The startup waveforms looks good. 

    Can you capture oscillatory behavior and help provide test waveform of Vin, Vout, GATE, input current (in a single scope shot) during startup, running, stop scenarios to debug the issue

    Best Regards, Rakesh

    --------------------------------------------------------------------------------------------------------

    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

  • In reply to Rakesh:

    Hi Rakesh

    Thanks for replying.

    Here is the waveform during startup, running and the oscillation

    Yellow is input current, blue is output voltage, green is MOSFET gate.

    https://imgur.com/a/0d60ljf

    Today I found out that even if just place a current probe at the robot, nothing inside the probe, oscillation waveform still appear.

    So I think there may be other things go wrong.

  • Guru 53675 points

    In reply to Hoi Keung TANG:

    Hi Tang,

    Why there is no inrush current during starting up 6000uF capacitance ?

    Do you see similar issue when running from a DC supply ? Can you add 220uF between source of motor switch and ground and check 

    Best Regards, Rakesh

    --------------------------------------------------------------------------------------------------------

    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

  • In reply to Rakesh:

    Hi Rakesh

    Thanks for replying

    There is about 3A startup current of the motor, because the timer capacitor is 10uF, statup time takes 500ms.

    I tried these and all have the same issue:

    Power supply for the whole robot

    Power supply for robot, battery for motor

    Power supply for motor, battery for robot.

  • Guru 53675 points

    In reply to Hoi Keung TANG:

    Hi Tang,

    If the oscillations are independent of power source and LM5060 switch. Can you check with your motor vendor for the functional misbehavior and abnormal currents. 

    Best Regards, Rakesh

    --------------------------------------------------------------------------------------------------------

    To find the latest information on Power Switches, Visit www.ti.com/powerswitch 

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