• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 368 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8343S-Q1EVM: DRV8343S-Q1EVM

Marsh Cai
Expert 4235 points
Part Number: DRV8343S-Q1EVM

Hi experts, I have a question of DRV8343S_Q1.

When I test DRV8343S-Q1EVM, I find the start performances of the high side MOSFETs and the low side MOSFETs are different. There are some oscillations in the Vgs waveform of the high side MOSFETs, when it goes into the miller platform. However there is no oscillation in the Vgs waveforms of the low side MOSFETs. And when I increase the IDRIVE, the oscillation on the high side MOSFETs will be worse. 

I find the Power supplies for the high side drivers and low side drivers are different. For the high side drivers, the supplies are charge pumps. And for low side drivers, the supplies are linear regulators.

Is power supply related to the Vgs waveform? Is this the root course for this phenomenon?

  • 0
    TI__Mastermind 21805 points

    Hello Marsh,

    The gate drive waveform will depend on several factors including the gate drive current setting, the amount of current, and the direction of current (into or out of the phase node). How much current are you driving into your load, and how is your load connected? Increasing the gate drive current typically results in more oscillation in general.

    The low-side MOSFET is referenced to GND, which is a stable node. The gate drive signal is applied from the gate (GLx) to source (GND). The high-side MOSFET is referenced to the phase, which is not a stable node. The gate drive signal is applied from the gate  (GHx) to source (SHx).

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    TI__Expert 4235 points

    Hi Matt,

    I connected a 24V BLDC to the EVM. And the BLDC span without any load. The dc power source showed that the input current flew into the EVM was about 250mA. To Vgs of the low side mosfets, its miller platform is stable and the Vgs increases smoothly in any IDRIVE settings. To Vgs of the high side mosfets, only when IDRIVE is set under 15mA, the miller platform will be stable and the Vgs will increase smoothly. In the situation with more than 15mA IDRIVE, the oscillation occurs.

    Actually in daily use, we might seldom set a such low IDRIVE. But I am still curious about the phenomenon.

    The first pic is the waveform of the low side MOSFETs. The second pic is the waveform of the high side MOSFETs. Yellow curve is the Vgs. Blue curve is the Vds.

    Thanks,

    Marsh

  • 0 in reply to Marsh Cai
    TI__Mastermind 21805 points

    Hi Marsh,

    How are you measuring the high-side MOSFET VGS? Are you using a differential probe from GHx to SHx??

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    TI__Expert 4235 points

    Hi Matt,

    I measured the high-side MOSFET VGS by a passive voltage probe from GHx to SHx, and for low-side MOSFET VGS from GHx to SPx.

    The part number for scope is Tektronix 2024. The following pic may help you to understand.

  • 0 in reply to Marsh Cai
    TI__Mastermind 21805 points

    Hello Marsh,

    You cannot use a passive voltage probe to measure GHx to SHx because SHx is not ground. Please use two scope probes, one measuring GHx and one measuring SHx and do a difference measurement between the two in the scope function.

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    TI__Mastermind 21805 points

    Hello Marsh,

    Do you need any additional help on this thread?

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    TI__Mastermind 21805 points

    Hi Marsh,

    I'm going to go ahead and close this thread. If you have further questions, please click the "Ask a related question" button.

    Thanks,

    Matt