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DRV8837: motor is blocked, How to solve these problems in the intelligent door lock?

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Replies: 3

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Part Number: DRV8837

Hi

The DRV8837 chip used in the intelligent door lock, when the motor is blocked, is there any suitable solution?

What mechanism is used to protect the motor from stalling?

Are there customers who do smart door locks? How do they deal with these problems?

Thanks 

Best Regards

Elsa Duan

  • Hi Elsa,

    To clarify: by asking if there is a suitable solution, do you mean a solution to detect a motor stall or to handle it?

    To protect a motor from stalling, a mechanism utilized is current limiting. For example, the DRV8830 and DRV8832 have a current limiting feature.

    For the DRV8837, you can calculate how much current you will see in a stall condition and add a sense resistor between the GND pin of the device and GND. Then, by measuring the voltage across it with an ADC, you can find out if the stall current is reached. Note that doing this adds voltage offset to the ground of the device, so you must account for it in the rest of your pin voltages (e.g. nSLEEP).

     

    Hector Hernandez
    Motor Applications Team

  • In reply to Hector Hernandez Luque:

    For a specific design, how to choose this sense resistor? What are the requirements?
    What is the equivalent resistance of this chip when it is blocked?
    Can you provide a demo of DRV8837? We can try to connect the motor for a test.

  • In reply to user5707026:

    Hi user,

    To select the sense resistor, you need to determine a voltage across the sense resistor that, when amplified by a current shunt amplifier, the amplifier's output is acceptable voltage for the receiving ADC of an MCU (e.g. sense resistor sees voltages from 0.0V to 165 mV, the amplifier has a gain of 20, so the ADC will see voltages from 0.0V to 3.3V). the voltage can then be divided by expected current seen by the sense resistor while driving the load to calculate the sense resistor's resistance. You must also accound for the sense resistor to be rated to enough wattage.

    Not sure what you mean by equivalent resistance of this chip when blocked. Equivalent resistance across what pins, exactly?

    There is an EVM, http://www.ti.com/tool/DRV8837EVM, that you can utlize to evaluate the part in a demo.

     

    Hector Hernandez
    Motor Applications Team

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