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Original question:

DRV8962: Do we need additional inductor and RC to drive a large voice coil motor?

DRV8962: DRV8962 or similar

Joe Miller1
Intellectual 355 points
Part Number: DRV8962
Other Parts Discussed in Thread: DRV8837, DRV8703-Q1

Tool/software:

Dear Sir/Madam,

What is recommended if I need to drive a low frequency +/-1V (no DC) sine wave 40Hz into a 33uH inductor load. The inductor DCR is 0.15ohm. 
Perhaps a H-Bridge is not the best solution? Any thoughts are greatly appreciated.

Regards Joe

  • 0
    TI__Mastermind 44525 points

    Hi Joe,

    Thank you for your post. If you intend to use a PWM driver to modulate the PWM with a sinewave at 40 Hz and generate bipolar +/- output you must either use a full-bridge or a dual power supply driver circuit. We have several full-bridge drivers in our portfolio. You can pick one based on the supply voltage you intend to use and the output current drive to the load.

    The desired +/- 1V sinewave 40 Hz to a 33 uH, its load current will be dominated by the impedance at 40 Hz which would be Z = √(R² + XL²), R is the DC resistance of the inductor which I expect to be very low ohms and XL is the XL = 2πfL, f - frequency and L - inductance. At 40 Hz XL term may not be consequential, so current through the inductor will be defined mostly by its DC resistance.

    Based on this you can choose a full-bridge driver from our portfolio. I don't think the DRV8962 would be a suitable device, perhaps overkill. Let me know what supply voltage you want to used and the fPWM you want to use, the desired load current for the inductive load - let us know its DC resistance DCR. Based on this we can suggest a driver that may suit your application needs. Thank you.

    Regards, Murugavel  

  • 0 in reply to Murugavel4637
    Intellectual 355 points

    Dear Murugavel,

    Thank you for the reply.

    The impedance is very low at 40Hz, 8.3mR.
    The supply can be 5V or 12V and the PWM frequency is 20KHz. 
    I previously tried a simulation with the DRV8837, VM at 5V.
    With reconstruction filter (LC) the output is good however when the 33uH load is connected the output drops to mV.
    The inductor DCR is 150mR. The 100uH (0.6A) inductor for the reconstruction filter has a lower Isat than the 33uH (1.1A) inductor load.
    So load current would need to be less than 0.6A. Not sure if this is possible.

    A class AB style amplifier could be a good fit as there would be no need for the reconstruction filter.
    I am not sure if TI has a suitable device. 

    Any help is greatly appreciated. 

    Regards Joe

  • +1 in reply to Joe Miller1
    TI__Mastermind 44525 points

    Hi Joe,

    Joe Miller1 said:
    The impedance is very low at 40Hz, 8.3mR.

    With +/- 1 V drive the current via the inductor in question would be pretty high - the real component 1/0.15 = 6.67 A. The reconstruction filter must stay unsaturated for about 7 A, with safety margin ~ 10 A. That would be pretty sizable inductor. The DRV8837 may support only up to 1.9 A tops, not a suitable product for this level of drive requirement. You may want to consider a gate driver with external FETs for example the DRV8703-Q1.

    Joe Miller1 said:
    A class AB style amplifier could be a good fit as there would be no need for the reconstruction filter.
    I am not sure if TI has a suitable device. 

    This may be an audio grade product. You may want to post with a product from Audio amplifiers in your device subject. We represent motor drives. We do not have class AB style drivers. Thank you. 

    Regards, Murugavel 

  • 0 in reply to Murugavel4637
    Intellectual 355 points

    Dear Murugavel,
    Thank you again for the reply.
    Regards Joe