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DRV8320R: DRV8320 implement a STO functionality

Part Number: DRV8320R
Other Parts Discussed in Thread: DRV8320, DRV8350F, DRV8350R, LM5008A, DRV8353F

Hi,

I'm implementing a motor controller with a DRV8320, that needs a STO functionality. So far, the controller has

a structure like this:

Next to the enable pin and deactivating the PWM signals, a relay is used to power off the high side MOSFET drain voltage. The problem with this is, that

I cannot place too much capacitive load next to the MOSFETs and that leads to more ringing and further I am bounded

with the maximum current without getting to large in size with the relay.

So I found this paper from TI, that explains the implementation of a STO:

https://www.ti.com/lit/an/slyt780/slyt780.pdf?ts=1623358487385&ref_url=https%253A%252F%252Fwww.google.ch%252F

So from there, it should already be enough to deactivate the PWM aswell as disable the enable pin, right? So if this STO is enough,

there should be no need for a relay at all. If not, then I would like to put the relay on the DRV8320 driver power stage,

such that I can switch this low power device instead of the MOSFETs.

One more question about the DRV8320 I have is, what happens when I remove the power VDRAIN. Does the driver itself pulldown the gate driver outputs?

  • Hello Sebastian,

    I would recommend taking a look at DRV8350F, which has a TUV-approved STO safety concept available. You can click the "request" button on the prodiuct page.

    When VDRAIN is removed, the DRV8320 will still be driving the MOSFETs since the device is powered from the VM pin.

    Thanks,

    Matt

  • Hi Matt, thanks, I will have a look at the DRV8350F. About the VDRAIN, I tought about removing the whole power for the gate driver, including VM.

  • Hi Sebastian,

    Unfortunately, not on the DRV832x - VM actually powers the whole IC for DRV832x. The DRV835x has a different power architecture (LINK)

    Thanks,

    Matt

  • Hi Matt,

    I see, so I need to change to the DRV8350R. What I don't fully understand is, how the STO should be triggered (what generates the STO1 and STO2 signals?).

    So lets take two cases as an example:

    1.) The application is a fast pick and place machine, which has a safety door (STO1). So when a human enters the door, the machine triggers a STO1. What is the other STO in this case? Comes STO2 from the microcontroller, that controls the motor driver, when for example an application fault happens?

    2.) Let's take a treadmill as an example. When we assume the threadmill has no reed switch for when a human falls, but only a micrcontroller, that detects by a sensor, if a human is running on it, what are STO1 and STO2? So both signals come from the microcontroller where the application runs. 

    Further, can I use the DRV8350R like in this configuration:

    Such that I interrupt the VDRAIN voltage of the driver and the feedback comes also from the DRV8350R?

  • Hi Sebastian,

    For the STO concept, STO1 and STO2 are triggered by a safety MCU or a safety control. Two paths are required to achieve the highest SIL level in the case that a fault disables one of the two independent paths. And so both paths could be coming from the same source, but they are independence paths to increase the reliability of the system.

    Thanks,

    Matt

  • One last questions: Is the DRV8350RFH compatible from the pinout and footprint with the DRV8350RH? It seems, the DRV8350RFH cannot be bought yet, at least I find only DRV8350FH on mouser and digikey. I would prefer the one with the integrated buck converter.

  • Hello Sebastian,

    Unfortunately the DRV835x variants without the buck will *not* be qualified for STO. This is new information and we are actively working to remove references to those parts from the DRV835xF datasheet.

    Buck integration into the device changes the safety concept, and the DC/DC used (LM5008A) does not have any diagnostics to be properly integrated into a single-chip solution for STO.

    Thanks,

    Matt

  • Hi Matt,

    I don't fully understand your answer. So STO is only available on the DRV835xF without buck converter, namely DRV8350FHRTVR and DRV8350FSRTVR?

    Thanks,

    Sebastian

  • Hello Sebastian,

    That's correct. DRV8350F and DRV8353F are released. We will not be releasing a DRV8350RF and DRV8353RF.

    Thanks,

    Matt

  • Hello Sebastian,

    Do you need any further assistance on this thread?

    Thanks,

    Matt

  • Hi Sebastian,

    I'm going to close this thread for now. If you have further questions please click the "Ask a related question" button!

    Thanks,

    Matt