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DRV8302: DRV8302 measurement topology

umut candan1
Prodigy 110 points
Part Number: DRV8302

hello experts;

i have some problem

i use drv8302 

i can't understood  that topology below figure.because i did some simulation but still i didnt understand 

what does this topology do , what is its job ,i added the ss,

please could you help me

best regards

  • +1
    TI__Expert 3535 points

    Hi Umut,

    Voltage divider and capacitor

    The 10 to 1 voltage divider is to scale down the phase voltage down to the scale of the ADC on the MCU.  Let’s say that your ADC can read a voltage from 0V to 3V (or whatever the full scale is). So, if you have a back EMF or phase voltage from 0V to 24V, then the 10 to 1 voltage divider turns 0V to 0V and 24V to 2.4V. Which is between the 0 and full-scale measurable value of the ADC. As for the capacitor, this is a RC filter that helps smooth out some edges. It also helps filter out MHz noise picked up by motor phase wires depending on the value.

    The diode to Vcc

    There are times where the back EMF can rise higher than the supply voltage (or VDRAIN). This higher voltage shouldn’t go to the ADC after it’s divided because it’s too far out of the margin of the divider. We want to divert that energy away from the ADC.

    Thanks,

    Michael

  • 0 in reply to Michael Arrant
    Prodigy 110 points

    thank you expert 

    i wonder that the diode is 3v3 zener diode? because the simulation dont clamp extreme voltage 

    thanks again

    best regard 

  • +1 in reply to umut candan1
    TI__Expert 3535 points

    Hi Umut,

    The diode in the schematic is a shockley diode. This diode is here because if there is a large back EMF, then the 10 to 1 voltage divider may not scale the voltage down low enough for the ADC to handle (it could fry to ADC). This shockley diode is here to clamp to voltage to Vcc in the case that this happens. 
    In general operation, this diode is not conducting current, however when/if this back EMF happens, and the ASENSE node rises above Vcc, that's when the diode will start conducting current and clamp the voltage to Vcc.

    Thanks,

    Michael