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DRV8876: Need help setting Ripropri

Derek
Mastermind 9792 points
Part Number: DRV8876

Hello,

   I'm using a motor, 12V, no-load current=45mA, loaded current=200mA and startup current about 500mA. I'm testing with the DRV8876EMK. I used the pot to set VREF to 2.5V. With the motor running (I=45mA) I'm measuring 55mV on the V_IPROPRI test point. However, that is not what the calculated voltage should be.

First, the current flowing out of IPROPRI should be:

IPROPRI = Imotor * Aipropri = 0.045A * (1000uA / A) = 45uA

On the EMK, Rpropri is 1500 ohms. So Vpropri = I*R = 45uA * 1500 ohms = 67.5mV

However, the measured value is 55mV. Did I calculate this incorrectly?

Also, if I want to keep VREF at 1500V, then what value of Ripropri should I use, max current would be startup current at 500mA. From the calculations I got:

Ripropri=VADC / Itrip * Aipropri = 2.5V / (500mA / 1000uA/A) = 5kOhms

Is this correct? I'd like to go higher to get better signal at normal operating current but I don't want to risk tripping the over-current limit during motor startup current pulse.

Thanks,

Derek

  • 0
    TI__Expert 8985 points

    Hi Derek,

    Comments inline.

    "However, the measured value is 55mV. Did I calculate this incorrectly?"

    HH-> Calculated correctly.

    Where is the current being measured?

    Did you measure the Imotor at the same instance you measured the Vipropi?

    Can you measure the resistance the resistor has?

    "Ripropri=VADC / Itrip * Aipropri = 2.5V / (500mA / 1000uA/A) = 5kOhms. Is this correct? I'd like to go higher to get a better signal at normal operating current but I don't want to risk tripping the over-current limit during motor startup current pulse."

    HH-> Calculated correctly. Please note that the overcurrent limit is different from the current regulation, which is what you are setting. Please the following article for more info:

    https://e2e.ti.com/support/motor-drivers/f/38/t/850885?tisearch=e2e-sitesearch&keymatch=faq%3Atrue