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DRV8871: Derating issue in RLIM resistor

Gowri A
Prodigy 50 points
Part Number: DRV8871

Tool/software:

I'm experiencing a derating issue with the RLIM resistor in DRV8871DDAR. The calculated derating value is too high, resulting in resistor failure.

Details,

ILIM = 1.5 A

RLIM = 47K ohms (As per the RLIM calculation formula provided in datasheet)

VLIM = 69KV

I2R loss = 105.75 KW

Rated Power of my resistor which i have chosen = 0.1 W

Could you please provide guidance on how to reduce the derating value for the RLIM resistor.

  • 0
    TI__Mastermind 45265 points

    Hello Gowri,

    Based on the data shared by you ITRIP = 1.5 A which is the output current limit setting. This will not be the current flowing through the RLIM resistor. The current through the resistor will be very small. You can measure the maximum voltage (using an oscilloscope) on the ILIM pin and calculate the RLIM power dissipation using (V2 / R). For example if V was 5V, then power dissipation of the resistor will be 25/47000 = 0.53 mW well within the 0.1 W you mentioned. 

    In the DRV8871EVM, we use 0402, 0.063W, 1% resistor for RLIM. 

    Regards, Murugavel  

  • 0 in reply to Murugavel4637
    Prodigy 50 points

    Thank you for your response. Actually I'm currently unable to physically access the device to measure the Voltage on the ILIM pin using an oscilloscope.

    Could you please provide an alternative method on;

    1. Estimating voltage on ILIM pin from datasheet specifications?

    2. Using simulation tools to determine Voltage on ILIM pin?

    3. Any other indirect methods to derive the voltage on ILIM pin?

  • +1 in reply to Gowri A
    TI__Mastermind 45265 points

    Hello Gowri,

    Based on our estimation the 47k 0.1 W resistor you selected should work fine. The power dissipation will be significantly lower than 0.1 W. I showed the 5 V example because in most cases the voltage may be less than that. 

    Regards, Murugavel