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DRV8801A-Q1: Inductor in series between the H-Bridge outputs

Denny Varghese
Prodigy 160 points
Part Number: DRV8801A-Q1

Hello Team,

Kindly help me with the calculations required to find the value of Inductor which should be kept in series with the MOTOR winding between the H-Bridge outputs. This Inductor is used to limit the inrush current along with a capacitor and resistor. (Capacitor and Resistor which are connected in series are placed between one end of the Inductor and the ground)

Motor Type: Brushed DC Motor

Load (Motor) Voltage: 24 V

Motor Peak Current: 0.7 A

Thanks,

Denny

  • 0
    TI__Guru 56650 points
    Denny,

    1. Motor winding between the H-Bridge output.
    2. Inductor in series with motor winding
    3. Capacitor and Resistor are connected in series are placed between one end of the Inductor and the ground
    Can you draw your circuit? You mean the RC is between motor and inductor joint and ground.
  • 0 in reply to Denny Varghese
    Prodigy 160 points
    Hi Wang, That's right, it's a RC circuit. Please find the attached circuit details and help in calculating the correct value of the Inductor capacitors and resistors.
  • 0 in reply to Denny Varghese
    TI__Guru 56650 points
    Denny,

    I don't have any concern about the inrush current on C1 and C2 if they are ceramic capacitors.
    For the inrush current on R1, please provide R1 peak current or power curve with different pulse width. C1 is only 0.01uF. I don't have a big concern if R1 is bigger than 0805 package. You can treat C1 and R1 as a RC snubber for switching circuit. The power loss on R1 is C1*Vin^2*fs and make sure it below R1 power limit.
    Where do you get that circuit? Please check the original designer about the L1's purpose.
  • 0 in reply to Wang5577
    Prodigy 160 points
    Hi Wang,

    We are not sure about the exact purpose of this inductor. It was present in original design and we don't have any design information about it.
    We assume, it has been placed for any of the following reasons:

    1) To prevent the back EMF.
    2) To prevent the inrush current, we can add a pair of inductors between the H-Bridge terminals.
    3) Even though the motor itself is an Inductor, it may have a low inductance, so extra inductance is added to help smooth out any current fluctuations when using PWM drive.

    Please provide your suggestions on this.

    Thank you!

    Best Regards,
    Denny
  • 0 in reply to Denny Varghese
    TI__Guru 56650 points
    Denny,

    Thank you for your input.

    To me, I would think it is for OCP detection. As you side, Even though the motor itself is an Inductor, it may have a low inductance, so extra inductance can help control the peak current under OCP threshold before the OCP detection blanking time expired. If the inductance is too small, the inductor current could be higher than OCP threshold before motor drive IC detect it. In such case, it is hard to do the current control. So, the calculation would be Lseries > [VM*t(DEG)/I(ocp)] -Lmotor

    I don't have much concern about the RC. That is why I ask. Thank you for your explanation.
  • 0 in reply to Wang5577
    Prodigy 160 points
    Hi Wang,

    Thank you very much for the details.

    Thanks,
    Denny