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DRV10975EVM: measurement of sinusoidal voltage with third order harmonics from phase to GN

Tina Chu
Prodigy 50 points
Part Number: DRV10975EVM
Other Parts Discussed in Thread: DRV10975, DRV10964

Hi there,

I am using DRV10975EVM to do some test practice, I would like to get the waveform like the diagram below , I have tried various inputs but still fail to get the result.
What input sources should I put to get the result? Is it PWM input or Analog input?

This diagram is from the data sheet of DRV10975.

Many thanks,

Tina

  • 0
    TI__Mastermind 18900 points

    Hey Tina,

    The waveforms you are referencing are the Phase to Phase voltage and Phase to GND voltage generated when driving the motor. A speed command—in the form of an analog signal or PWM signal into the SPEED pin or over I2C—is enough to get start driving the motor. More information about can be found in the datasheet in section 8.3.3.

    If you have the GUI, an easy way to control the speed is to go to the Display tab, check the OverRide box (to enable speed via I2C) then type a value in the box.

    For observing the wave form, I’d recommend entering a high speed command and then entering a low speed command to get the motor to “coast” to the lower speed. But you should be able to observe these voltages whenever the motor is being driven.

    I will say that, depending on the bandwidth of your oscilloscope, you might see the waveforms look more distorted than the nice figures shown in the post and the datasheet. This is because the PWM, Analog, and I2C speed commands are translated into PWM signals that will drive the internal FETs. As a result, you are observing these PWM signals (as demonstrated below).

     

    If you limit the BW of your scope or have other methods of filtering the signal, you should see the waveforms clear up and look like the figures in the datasheet.

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 50 points
    Hi Cole,

    Just like you mentioned, I got the clearest waveform with PWM input, and others are pretty distorted.
    Thanks for your answering.

    Tina
  • 0 in reply to Tina Chu
    TI__Mastermind 18900 points
    Glad to hear you got the waveforms! Let me know if you need anything else.

    Best,
    -Cole
  • 0 in reply to Cole Macias
    Prodigy 50 points

    Hi Cole,

    I am doing deep study of the functional block diagram in DRV10975 datasheet, and I am wondering some of the electronic elements' purpose and their functions.

    1. Is the charge pump for doubling the supply voltage in order to produce larger voltage for elements(predriver and high-side mos) that need higher voltage than the supply voltage?

    2. What is the function of the V/I sensor?

    3. Does the oscillator act as a DC to AC converter to produce signals like sin wave to the logic code?

    4.What is the purpose and function of the bandgap? 

    5.Is it pre-driver who send the controlling signal to MOS?

    Thank you so much for your help,

    Regards,

    Tina

  • 0 in reply to Tina Chu
    TI__Mastermind 18900 points

     Hi Tina,

    Apologizes for the delay. Let me answer your questions directly:

    1. Is the charge pump for doubling the supply voltage in order to produce larger voltage for elements(predriver and high-side mos) that need higher voltage than the supply voltage?

    You’re mostly right with this one. Not necessarily doubling, but we do need a voltage that is a threshold voltage higher than VCC to turn on the High side FETs. This is where the charge pump comes in.

    1. What is the function of the V/I sensor?

    As you may have seen, we have many protection circuits such as overcurrent, voltage surge, under voltage lock out, etc. We also need a way to mointor Back EMF (BEMF) and estimate current. As a result, we need this V/I sensor to monitor for these.

    1. Does the oscillator act as a DC to AC converter to produce signals like sin wave to the logic code?

    I think the better way to look at the purpose of the oscillator is to generate the clock and timing signals used in the device. 

    1. What is the purpose and function of the bandgap?

    Bandgap refers to a Band Voltage reference. We need the voltage references for the logic core and a few other places.

    1. Is it pre-driver who send the controlling signal to MOS?

    Yes, it is the Pre-driver that eventually translates the digital signal to the analog signal that is sent to the gate of the MOSFET.

    Hope this helps!

    Best,

    -Cole

     

  • 0 in reply to Cole Macias
    Prodigy 50 points

    Hi Cole,

    Thanks for your answering, and I also have some question for the external circuit of 10975.

    There are some capacitors and resistor connected to pins.

    For the power pins, such as VCC, VCP, CPN and V1P8, V3P3, I think they are placed at the pin as an AC filter, is it correct?

    And I am also wonder what is the purpose of the resistor and capacitor at pin 4?

    Is it okay to ask question of DRV10964 here? or should I post a new post?

    I will remove 10964's question from here if I need to post a new one, thanks.

    This is functional block diagram of 10964, and I don't understand why a mos is connected to pin FG?

    Many thanks for your answering,

    Regards,

    Tina

  • 0 in reply to Tina Chu
    TI__Mastermind 18900 points

    Hey Tina,

    I want to differentiate between the two cap configurations you’re seeing:

    The capacitors that go from VCC, V1P8, and V3P3 to GND, these are called decoupling capacitors. Perhaps you’ve heard of them, they are used to filter or clean up the power signals. If there is a small dip in voltage, on say VCC, the decoupling capacitors should be able to discharge and bring VCC back up to its intended voltage.

    The capacitors that are connected between VCC and VCP and CPP and CPN, are capacitors needed for the charge pump to operate correctly. Essentially, these capacitors are rather large to be built into the die of the device (using PN junctions) so the device is kept smaller by building some of the charge outside of the pump. If you want to learn more about charge pumps check out The Forgotten Converter app note.

    The resistor and capacitor refer to the step down regulator shown in section 8.3.1.1 in the datasheet. I’ve posted a screenshot of it here. One important note of information is that this step down regulator steps down VCC to 5V then the 5V is used for the 3.3V and 1.8V LDO voltages. So just like the charge pump, we are building the regulator outside of die of the device.


    For more info on the values and voltage ratings of each component, check out table 11 in section 9.2.1 of the 975 datasheet.

    Also, yes please make a separate post in regards to the DRV10964, this’ll make it easier for other people to search for questions related to the 964 in the future. Then I’ll answer it there.

     

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Prodigy 50 points

    Hi Cole,

    Thanks for your answer.

    For the V/I sensor, is the input voltage or current? and same question for the output, is it output current orvoltage?

    And I don't really understand what are the lock out and woke up voltage for UVLO, should I add the hysteresis of UVLO threhold to the Uuvlo_F and Uuvlo_R?

    Thanks a lot,

    Regards,

    Tina