• State Resolved
  • Locked Locked
  • Replies 17 replies
  • Subscribers 31 subscribers
  • Views 8308 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.

DRV595: Getting very hot

Aby169
Prodigy 230 points
Part Number: DRV595

I am using the DRV595 to drive a 7V, 1A TEC and I have an overheating issue on a new project. The conditions are:

 

  1. Power supply voltage of 7V

  2. Ambient is 25C

  3. Max TEC current is 1.1A (full drive)

  4. According to those figures I should be dissipating only 0.13W across the two internal output transistors 1.1A x 1.1A x 60mOhms x 2

  5. In theory, this gives me a temperature rise of only 3.3 degC above ambient

  6. The layout of the PCB is according to the data sheet with thermal pad and thermal vias.

  7. The switching frequency is set to 1MHz
  8. The device works until it gets hotter (when fully driving the TEC) until it goes into the fault condition.

 

The symptoms are:

 

  1. The DRV595 is going into FAULTZ condition and turning off the output

  2. The temperature measured on the top of the package of the DRV595 is in excess of 60degC

 

Any ideas what is happening here or have I just got the math totally wrong!

  • 0
    TI__Expert 6985 points
    Hello! Shawn should be able to close with you on details, but first a quick question... how much time are you experiencing to shutdown? Thanks!
  • 0 in reply to Jeff Kohnle
    Prodigy 230 points
    Hi Jeff,

    It shuts down until I reset the device (remove power). If I connect FAULT pin to SD pin then resets automatically after a brief shutdown. I know it is an overheating issue as I can apply freezer spray on it and it prolongs the time before it shuts down.

    Thanks.
  • 0 in reply to Aby169
    TI__Expert 6985 points
    Hello! Thanks for the feedback. Shawn will take a look at this and get back to you.
  • 0
    TI__Mastermind 24835 points
    Hi Abdul,
    Could you please confirm the maximum output current is 1.1A? If it's, it's far from the over-current threshold, and the FAULT can't be a over-current FAULT. Is the power supply stable at 7V? If it is, the FAULT is not a under-voltage FAULT or over-voltage FAULT on PVCC.
    Then the only possibility is over-temperature FAULT. But the output power is actually very low (less than 1.1A), and the temperature shouldn't rise too much. The over-current FAULT shouldn't occur with Ta=25degC if PCB design follows our EVM www.ti.com/.../slau479.pdf.
    This sounds strange. Could you plesae send me your SCH and PCB? And could you capture the waveform of output current signal when the FAULT occurs?
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 230 points

    Hi Shawn,

    I can confirm that the voltage Is 7V and the current is no more than 1.1A. I attach the schematic and some waveforms on the relevant pins when the fault occurs.

    Please take a look.

    Thanks

    Abdul.DRV595 Getting Hot.zip

  • 0 in reply to Aby169
    TI__Mastermind 24835 points
    Hi Abdul,
    Please try 400kHz PWM switching frequency, see if the FAULT still occurs. Let me know if it works.

    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 230 points
    Hi Shawn,

    I have just tried that with no luck.

    I am now thinking this may be a cause and effect. I am measuring the IN+ pin. On this pin the signal is a PWM filtered by a LP filter which is made up of C54 and R52. C54 is 100uF and R52 is 10K. I am wondering if this is causing a problem on the input. Is there a maximum input capacitance or minimum current etc? When I put my scope I notice that this voltage jumps from 200mV (max drive) to about 400mV at about the same time as the unit resets itself? Or is this what you would expect on this pin after/during a reset?

    Thanks
  • 0 in reply to Aby169
    TI__Mastermind 24835 points
    Hi Abdul,
    It's not expected that the input voltage jumps from 200mV 400mV. I think you can try with a lower value capacitor on INP and set DC bias voltage on INN pin to 3V.
  • 0 in reply to Shawn Zheng
    Prodigy 230 points
    Hi Shawn,

    I have removed the capacitor and resistor and grounded the INP. The output is now hard on and driving my TEC down. But again it is resetting. The reset is occurring approximately every 90seconds.

    Thanks.

    Abdul.
  • 0 in reply to Aby169
    Prodigy 230 points
    Hi Shawn,

    To verify that the TEC is not shorting and hence casing the problem, I replaced the TEC with a power resistor, drawing about 0.7A. The same problem remains.

    In all the testing done so far, I noticed that the DRV595 does not feel exceptionally hot to the touch, it measures about 30degC on the surface of the chip.

    Any more ideas?

    Abdul.
  • 0 in reply to Aby169
    TI__Mastermind 24835 points

    Hi Abdul,

    So the temperature is not very high when the issue occurs, right?

    Could you please try a simple experiment. Remove all of the connection on the input pins - INN and INP. Just connect the two input pins to GND through a 0.1uF capacitors. No input signal or bias viltage on input. In this case, the voltage on input pins should be around 3V. See if the FUALT is still triggered.

    Is it possibly a solding issue? Or does this issue occur on every device and every board?

    Best regards,

    Shawn Zheng

  • 0 in reply to Shawn Zheng
    Prodigy 230 points
    Hi Shawn,

    I think I may be getting closer to the cause.

    My INN is fixed at 2.5V. The problem seems to occur only if INP goes below 1.8V. So when the voltage across the 2 input pins is >0.7V we have this FAULT problem. Now the gain is 20dB.

    So is this because the input difference voltage is too high?

    What do you think?

    Thanks
    Abdul.
  • 0 in reply to Aby169
    Prodigy 230 points

    Hi Shawn,

    Any thoughts on my previous post?

    Thanks

    Abdul.

  • 0 in reply to Aby169
    TI__Mastermind 24835 points
    Hi Abdul,
    How much is the load? When the input is 0.7V and 20dB gain, the output voltage is around 7V. If the load is very small and the continuous output current is larger than 4A, OT FAULT occurs. Or if transient output current is larger than 7.5A, OC FAULT occurs. Please check the load and whether there is short circuit on the output.
    Could you measure the output current by scope? Capture two signals(Ioutput and FAULT) to see how much current the device is outputing when the FAULT occurs.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    Prodigy 230 points
    Hi Shawn,

    As mentioned before, the load is no more than 1.1A. The output voltage (the DRV595 supply voltage) is 7V. There is no short circuit.

    What I am trying to highlight is that as long as the differential voltage between the input pins is <0.7V we have no problem. So it seems that the problem is not due to OT, SC or OC. It is more related to the input voltage differential (and the gain)

    Regards,

    Abdul.
  • 0 in reply to Aby169
    TI__Mastermind 24835 points

    Hi Abdul,

    The FAULT on DRV595 can only be OT FAULT or OC FAULT. There shouldn't be any problem when input differential voltage is 0.8V or 0.9V. Could you please check the power supply, is it always stable at 7V? Does this issue occur on only one board or all the boards? What if you change another device on the problem board?

    Best regards,

    Shawn Zheng

      

  • 0 in reply to Aby169
    TI__Expert 6985 points
    Hello Abdul, Did you solve your problem? thanks, Jeff