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DRV8412 without PWM

Filo
Prodigy 40 points
Other Parts Discussed in Thread: DRV8412, DRV8840, DRV8829, DRV8842, DRV8842EVM

Hello,

I want to drive two brushed DC motors (about 3A RMS each) using DRV8412 with basic left/right/stop control, no PWM. There is a section in the datasheet named "Bootstrap Capacitor Under Voltage Protection" saying that I need to increase bootstrap capacitance when using low frequency PWM. Since I want to use fixed levels, it will trigger under voltage protection. Will the DRV8412 work with simple logic drive? How big should then the bootstrap capacitor be? What will happen if I apply 100% duty cycle - will it drive the motor close to that duty cycle?

Thanks

  • 0
    TI__Guru** 114905 points

    Hi Filo,

    The DRV8412 will not work under the condition you describe. At 100% duty cycle, the bootstrap capacitor voltage will eventually drop below the BST_UVP threshold. At that point, the high side driver will turn off.

    Is there a reason you would like to use the DRV8412, such as voltage? The DRV8829 and DRV8840 can drive similar current, although you need 2 devices and they do not operate at the same voltage.

    If you desire to remain with the DRV8412, please change the duty cycle to almost 100%. As noted on page 11 of the datasheet in the section "Bootstrap Capacitor Under Voltage Protection", "it is recommended to turn on the low side FET for at least 50ns for each PWM cycle". 

  • 0 in reply to Rick Duncan
    Prodigy 40 points

    Thanks for help. The motors are powered by 36VDC. I initially picked DRV8412 because of two drivers in one IC. I need something as simple as L298, but little bit more powerful and with protection circuitry. In the end I will use two DRV8842.

  • 0 in reply to Filo
    TI__Guru** 114905 points

    Hi Filo,

    The DRV8842 is a good choice for your application. If you are interested, the DRV8842EVM is available to evaluate the device. Also, the schematic and layout of the EVM are available for reference.

    The EVM can be found at http://www.ti.com/tool/drv8842evm