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Original question:

DRV8809 shutting down

DRV8809: DRV8809 random TSD

Gabby Nunez
Prodigy 40 points
Part Number: DRV8809

Hi,

I’m having an intermittent problem with the DRV8809 doing a thermal shutdown (TSD). I noticed it tends to happen when the motors (2 steppers) are moving, but I don’t think the chip is actually reaching the shutdown temperature.

I’ve confirmed a TSD is happening by looking at the LOG_OUT pin and playing with the TSD operation (bits 13-15 of the extended setup register).

I tried to monitor the temperature by configuring TH_OUT as an analog output (setting bit 12 on the extended setup register) and connecting an external pull up resistor to 3.3V. The voltage is always close to 3.3V, even when the motors are running, which I assume means that it is not heating up too much.

I then configured TH_OUT as a digital output (Pre-TSD) to see if I could at least see a warning before the chip actually shut off, but the Pre-TSD signal does not assert before the TSD signal, even though it should be coming 20° before the TSD.

The only way I’ve been able to “fix” the issue is by disabling the TSD (bit 7 of extended setup register), but I’m not sure if that’s dangerous.

Any ideas why it would randomly issue a TSD? And why the Pre-TSD does not trigger before the TSD??

Thank you!

PS: My problem sounds very similar to the one described in the following link but I could not see a solution. (http://e2e.ti.com/support/applications/motor_drivers/f/38/t/343406?DRV8809-shutting-down).

  • 0
    TI__Intellectual 1965 points
    Hi Gabby,

    Thanks for your question. Please let me contact the engineer who supports this part. They should respond to your question before June 29th.

    Best,
    Grant
  • 0 in reply to Grant Falkenburg
    TI__Mastermind 44835 points

    Hi

    Here is two possible scenario may cause this type of issue.

    - VCP voltage is not proper by some reason(Damaging part etc). VCP should be VM+10V range. If it is lower, die temperature quickly goes up when motor is running.

    -Thermal pad soldering condition is not proper. If thermal pad does not connect to GND plane, die temperature quickly goes up when motor is running.

    If die temperature goes up quickly due to above condition, shutdown may happen before PreTSD comes out.

    regards

    Shinya Morita 

  • 0 in reply to Shinya Morita
    Prodigy 40 points

    Thank you for the response.

    I measured the VCP voltage and it's usually steady around VM+11V. However, I noticed that when the motors are running, sometimes I see a fast spike that drops the voltage to VM+5V and back up to VM+11V. 

    The circuit has been designed to the datasheet spec and I'm not sure what is causing VCP to fluctuate.

    My questions are:

    1. Could there be a problem with the charge pump that causes this fluctuation?

    2. What are some things that could affect the VCP voltage?

    3. Does a low VCP really cause the die temperature to exceed the shutdown limit, or is it just falsely triggering the TSD signal?

    Thank you!

  • 0 in reply to Gabby Nunez
    TI__Mastermind 44835 points
    Hi,
    I am feeling drop from +11V to +5V is a little high, but I do not have data on my hand. One thing I may try is to increase VCP cap from 0.1uF to 0.47uF. If VCP is not high enough, we could not fully turn on high side NMOS FET, then high side Rdson gets higher. It brings high Ploss and heats up IC.

    I noticed that your measurement way for TH_OUT as an analog output is not correct. We should remove 3.3V pull up for this mode. I would recommend to remove pull up and check TH_OUT analog.

    regards
    Shinya Morita
  • 0 in reply to Shinya Morita
    Prodigy 40 points

    Hi,

    I replaced the VCP cap with 0.47uF and it did not help. It still goes down to around VM+5V.

    I also removed the 3.3V pull up and measured TH_OUT as an analog output. When the motors are not moving TH_OUT is 1.8V and when the motors move TH_OUT is 1.9V. It does not look like it is getting hot according to the Tsense plot in the datasheet.

    Since TH_OUT is not going beyond 1.9V when TSD is happening, does it mean the chip is falsely triggering a TSD?

    Any other ideas/suggestions??

    Thank you

  • 0 in reply to Gabby Nunez
    TI__Mastermind 44835 points
    Hi,
    It is strange that TH_OUT shows lower temp, but you verified it was shut down by TSD.
    >>>>>>>>Your comment :The only way I’ve been able to “fix” the issue is by disabling the TSD (bit 7 of extended setup register), but I’m not sure if that’s dangerous.

    I am guessing that power pad connection could be potential root cause. If power pad connection is not proper, die can be heat up quickly then TSD happens. This device requires the power pad is well soldered down to GND plan through via.
    Here is the link for reference info.

    www.ti.com/.../slma002h.pdf

    Thanks,
  • 0 in reply to Shinya Morita
    Prodigy 40 points

    Hi,

    From our design, we do have a connection to the grounding pad. We also have a large pad and some runoff traces to try and get some of the thermal rise under control. We also take measures to ensure that the pads are correctly joined to the solder.

    The problem is happening really quickly, and the thermal rise shouldn't be in the millisecond range. We also used one of your older chips, the TPIC70600 and are not seeing this same issue occur (it also uses this same pad and structure).

    Anything else you can think of?

    Thank you!

  • 0 in reply to Gabby Nunez
    TI__Mastermind 44835 points
    Hi,
    It is very wired. Good PCB layout shuld have range of 20-30C/W. So we can handle 2.x W range normally. If you run all 4 motor drivers at the same time, it may heat up quickly by exceeding 2.x W. My suggestion is to reduce motor current or disable some of motors.
    Unfortunaely i do not have ideas anymore. I believe this is not just one part issue which is broken.