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DRV8312 -> USER_ADC_FULL_SCALE_CURRENT_A define valve question?

hong sungho
Prodigy 70 points
Other Parts Discussed in Thread: DRV8312, DRV8301

Hello.

control of the speed tests using a used DRV8312 Kit and TMS32F28069M

Question of the values defined in the kit  USER_ADC_FULL_SCALE_CURRENT_A (17.30) ?

find the datasheet "InstaSPIN-FOC™ and InstaSPIN-MOTION™ User's Guide" 17.6.1 - The differential gain of this circuit is 19.08 V/V. R52,
R53, and R50 are shunt resistors for each phase and are 10 mM each. The amount of current that causes
a 3.3 V output to the ADC is 3.3/.010/19.08 = 17.30 A/V.

Question  19.08 V/V -> I want to know  transfer function of this circuit equation

Thanks in advance!

  • 0
    TI__Expert 5180 points

    The transfer function, taking current as the input, and ADC pin voltage as the output, would be:

    Current * (3.3/17.3) + 1.65 = VADC

    Where current can be from -17.3/2 to +17.3/2

    If you are designing a new hardware, I suggest you do the differential amplifier done in the DRV8301 kit. That equation of that diff amplifier is much more straight forward, and since both rails have the exact same gains, it acts better as a differential amplifier, filtering common noise.

    -Jorge

  • 0 in reply to Jorge Zambada
    Prodigy 70 points
    My question?

    DRV8301 reference diagram below, the resistance Rfbk is different, Is also a power source REF 2.5V.

    In this case, the equation is not satisfied, and provided in the 14.InstaSPIN-FOC™ and InstaSPIN-MOTION™ User guide. 5.2.1(Current feedback gain) Equation 3.

    How that DRV8301 the 19.08V based on the circuit  is calculated?

    Sung-ho

  • 0 in reply to Jorge Zambada
    Prodigy 70 points

    Thanks to answer my question?

    DRV8301 reference diagram below, the resistance R108, R105 is different, Is also a power source REF 2.5V.

    In this case, the equation is not satisfied, and provided in the InstaSPIN-FOC™ and InstaSPIN-MOTION™ User guide.(5.2.1-Current feedback gain, Equation 3)

    How that DRV8301 the 19.08V based on the circuit is calculated ?

    sung-ho.

  • 0 in reply to hong sungho
    TI__Expert 5180 points

    Take a look at this other post that talks about feedback resistors being different, and Vref being different.

    https://e2e.ti.com/support/microcontrollers/c2000/f/902/t/357169

    However, if this is for a new design of yours, I STRONGLY recommend using a differential amplifier circuit like the one we have in the 8301 board, to get the best noise immunity when you sample your currents.

    -Jorge