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DRV8350R: DRV8350R Stop working

Part Number: DRV8350R
Other Parts Discussed in Thread: CSD18511KTT, DRV8350, CSD19535, CSD19536

Dear all,

we work with DRV8350R and CSD18511KTT on a BLDC. in normal all functions are good. We speed up with little ramp up, turn until an current of approx. 100 Ampere is reached, ramp down in 53 ms and then we turn some secons in other direction. Now sometimes the BLDC stop without any change of signal and it sounds like the BLDC is turning with full speed in other direction, no ramp down.

On which position can I search for this problem?

We work with 18V. I think that this problem orccur more when the MOSFET is hot. Approx. 70°C. We use the DRV8350 with lowest IDRIVE setting. 

One time the problem or error comes up, in next try everything is good again. Then again the problem after some times.

Thank you for help.

  • Peter,

    Thanks for posting on the MD forum!

    I'm not sure what issue you are experiencing, could you explain it differently, show a video or a scope image?

    Regards,

    -Adam

  • Hi Adam,

    sorry for the late answer. I don't have a image or video but it sounds like High-Side MOSFET and Low-Side MOSFET switch ON in same time. Motor stops immediately and current measurmente show very high value. This effect start at 75°C outside from MOSFET (measured with NTC) and comes up from time to time. Also some time tool stop immediately after run up in 100 ms. Then we have to wait some minutes and everything is good. Temperature outside from MOSET goes up to 120°C. 

    Sounds like MOSFET switch ON because it is to hot? We go up to 160 Ampere! Maybe we have to test other MOSFET?

    - Peter

  • Hi Adam,

    I have did one more test and you can find two scope pictures. I have compared the switching of motor voltage from DRV8350 (first picture) and a drill from a shop (second picture). I can see, that at my controller the voltage goes very low in a ramp, at the controller from the shop the voltage is more stabel. The voltage don't go down so much. I have tried 20 kHz and 40 kHz but the result ist the same. DRV8350 switch the voltage very low? Can this be a problem for MOSFET or is this a problem / behavior of the DRV8350? When yes, can i change anything?

    Attached you can find the schematic of the power part. Seems like the MOSFET don't switch complete On? We have approx. 160 Ampere.

    Thank you!

  • Peter,

    Thanks for the information. The schematic looks correct to me. 

    As for the plots, could you retake them showing the differential voltage from Gate to Source of both the high side FET and low side FET?

    We need to check the switching waveform of the Vgs for high and low FETs.

    Which signals were shown in the previous plots you sent?

    Regards,

    -Adam

  • Adam,

    the plots show in first picture the voltage at the windings U and V driven with DRV8350. Second picture is voltage at windings from power tool I have bought in a worker shop. DRV was connected to the same motor, so I only replace the controller unit! So I directly can see and hear, that at upper torque DRV don't control like original controller. Plots show the same!

    Tomorrow I can plot the VGS from DRV controller, at the bought controller I can't do this because it is closed and I can't open it without damage.

    What can I try to change to test more?

    Switch current from DRV with resistor at IDRIVE?

    Lower Switch frequency?

    What about boost capacitor? Is this to small for such high loads? In free run the plot show the same from DRV and bought tool, only bought tool is a little bit faster but only 10 RPMs.

    What I can see, that with my controller and DRV the power supplies go down to 12 - 13 volt (like see at the plots) but not with the bought controller.

    Thank you for help.

  • Peter,

    We don't need info or plots for the bought controller, only the DRV board.

    Once we see the detail of the Vgs voltages I can suggest more tests or conditions to change.

    Regards,

    -Adam

  • Adam,

    I send the plots of high side and low side VGS tomorrow. 

    What did you think about C14, C17 and C18? Are this to small?

    Controller is connected to 18V batterie and we need 160 Ampere. 

  • Hi Adam,

    attached are the plots of VGS from one Highside MOSFET from Gate to source (picture one and two) and Lowside Mosfet from gate to source (picture 3)

    Picture 4 is a plot from power supply input. I think here is the problem. If I compare this with the bought tool, the power supply only have some spikes but 95% is a line.

    We have also placed a 1000uF capacitor between VM (batterie input) and GND. But result is the same!

    Regards,

    Peter

  • Hi Adam,

    any idea what I can try?

    Regards,

    Peter

  • Hi Adam,

    I hope you come back to this thread.

    What did you mean about a to short dead time? Is this possible? We use the fixed dead time of 100 ns and synchron 1 PWM mode. Can this be a problem with the MOSFET?

    One question for the VGS Handshake from DRV8350. What is the voltage on which this handshake occur? I see, that on DRV8350-EVM the MOSFET has a VGS of 2,6 Volt, we use MOSFET with 1,8 Volt. Can this be a problem?

  • Hi Adam,

    I will try CSD19535 which I have See in lot of designs from TI. Maybe this work. Otherwise I will change to DRV with serial port SPI.

  • Peter,

    Sorry for the delay here. If you can use an SPI device then this would help us to debug a lot.

    The DRV8350 VGS handshaking should happen at around 2V.

    It looks like your low-side VGS is very noisy, it's possible that you are getting partial turn on of the LS FET when there is lots of current through the bridge. Can you share the layout so we can comment?

    Since your FETs have a very low turn on this may make the problem worse. I would try the FETs you mentioned above.

    Also, can you check if the VCP node has any fluctuation during the same test? We want to correlate the noise on the high side and low side VGS with any potential VCP issue.

    Regards,

    -Adam

  • Hi Adam,

    thank you for your response. Attached one more plot. Yellow line ist measured on VCP (PIN7) and GND. Same line like measured on VM and GND (Batteryconnection). Blue line is LowSide from Gate to Source. Sometimes I can see spikes up to 10V but can be Synchron PWM.

    The second picture shows a plot from Highside Gate to GND (yellow line) and Lowside Gate to GND (Blue line). Could be the position when Lowside MOSFET switch of and Highside get current from motor windings. The is no signla from DRV to Gate from Highside (we have plot from Gate to source at highside) but we can see the voltage between Gate and GND from Highside.

    Attached a PDF with our Layout.

    We will try SPI Version of DRV8350 and MOSFET CSD19536 (We have soldered six on one PCB but this damaged our driver, but is possible that we have a problem as we soldered it).

    Also we will try Asynchron PWM with longer deadtime.

    Thank you for your help.

    Regards, Peter

     5611.Layout.pdf

  • Peter,

    The first image is helpful but we would like to see it zoomed in more, could you repeat it with ~200uS per division?

    Also we are trying to correlate High Side Vgs to VCP and Low Side Vgs to VGLS. 

    If you have a two channel scope, please make one plot of VCP and High Side Vgs, a second plot of VGLS and Low Side Vgs.

    As for the second plot, please check the Switch node voltage when you check the high side gate voltage because the gate-to-source voltage decides if the high side FET is on, not only the gate voltage.

    Can you email me the layout as an altium file or similar? Adamsidelsky(at)ti(dot)com.

    Regards,

    -Adam

  • Hi Adam,

    thank you again for your help. I will try my best to send you tomorrow the requested plots.

    One more question. What did you mean witch "Check the swtich node voltage when you check the high side gate voltage"?

    Regards,

    Peter

  • Peter,

    Measuring the high side gate voltage is not the full picture as the High side FET is only on when there is sufficient voltage between it's gate and source pins, the Vgs. 

    It's possible for both the gate voltage and source voltage to be high which may look like the HS FET is on but actually the Vgs is very low or zero which keeps the FET off. In fact when the HS FET is off, the gate and source are shorted to each other to prevent any Vgs from developing.

    Regards.

    -Adam

  • Hi Adam,

    attached a plot from high side FET from gate to source. Second is from high side gate to GND or source from low side.

  • Post is continuing over email, I will update this thread when we have more info.

  • Layout suggestions have been given and new board has been ordered. Will comment back with updates.

    Regards,

    -Adam