This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8847: (TSSOP Package)

Part Number: DRV8847

How to limit the current in drv8847PWR (TSSOP) motor driver, say if i need only 50mA current as after that the my connected device will get damage, how to get this amount of current only. If it can be done through some equations, Kindly guide this with its details and the recommended operating value or the pwm on time change can help me in limiting the current to 50mA value or any thing else of our choice. 

  • The DRV8847 has a current regulation feature that can be used to limit the output current. Please refer to Section 7.3.4 in the datasheet. The guiding equation is given by:

    where,

    • ITRIP is the regulated current.
    • VTRIP is the internally generated trip voltage.
    • RSENSExx is the resistance of the sense resistor
    • Torque is the torque scalar, the value of which depends on the input on the TRQ pin. TRQ = 100% for TRQ pin connected to GND and TRQ = 50% connected to VEXT.

    As an example, VTRIP=5V and RSENSExx=100ohms with TRQ pin connected to GND renders an ITRIP current of 50mA. 

  • Thank you sir for your response but if the Vtrip is the internally generated trip voltage how can we set the Vtrip manually as 5v or anything else, additionally the suggested Vtrip value in the datasheet is 150mV only. Therefore, should we take it as 150mv only and proceed further by taking suitable rsense value that can lead to output current as 50mA following the equation or there is any other way to deal with vtrip. 

  • Hey Aanchal,

    You are correct, VTRIP is always 150mV ±10mV for DRV8847.  So yes, agreed, you would select a R_SENSE value to appropriately limit the current. 

    If this is a new design I recommend looking at a newer motor driver, such as DRV8425 where the current regulation setpoint is adjusted by the voltage at the VREF pin.

    Best,

    Jacob

  • Thank you for the response Mr. Thompson. This resolved my issue but just to be sure, can you confirm if we will use 3 ohm rsense resistor, with 1 as troque and 150mV as vtrip value, it will limit the current to 50mA for sure in real time use as i can't take risk with the connected device to drv8847

  • Hey Aanchal,

    RSENSE = Torque * VTRIP / ITRIP --> 1.00 * 0.150V / 0.050A = 3.0Ω

    Yes, I confirm that is correct for full-scale trip current of 50mA. 

    Best,

    Jacob