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DRV8662 constantly drawing ~400mA

Rui Chen58
Prodigy 240 points
Other Parts Discussed in Thread: DRV2700, DRV8662

Hi,

I have integrated a DRV8662 on my PCB accoring to the schematics below. At first the PCB seemed to work ok but since the first time I enabled the DRV8662 the PCB have constantly been drawing ~400mA as soon as power is connected. (before the DRV8662 was first enabled it was ~8mA). Disabling the DRV8662 does not help. I have connected the DRV8662 accoring to figure 35 in the DRV2700 manual (which should work for DRV8662 also). Is there anyone who can explain this behaviour and know how to fix it?

Thanks!

  • 0
    TI__Expert 3280 points
    Hey Rui,
    It would seem like the device has been damaged. Have you tried:
    1. Measuring any of the signals (VBST, OUT+/-, etc...)
    2. Replacing the device
    3. Removing the load

    These should give us some additional debug information.
  • 0 in reply to Rodney Miranda
    Prodigy 240 points

    Hi Rodney,

    1. VBST is constantly ~3V, the signal is quite noisy
    2. I havent replaced the device but I did the same thing (set enable high) on another PCB and got the same result. 
    3. I never connected any load to the new boards.

    I guess the DRV8662 must have been damanged somehow, but I dont understand why or how.

    I haven't done anything with the DRV8662 over the weekend but now it is constantly drawing ~1A, the current seems to decrease slighly over time after power has been connected. Have you seen this before?

  • 0 in reply to Rui Chen58
    TI__Genius 12485 points

    Rui,

    I was just taking a quick look at the schematic and it looks like you have connected the inputs to GND (esp. IN- to a strong ground). The datasheets recommends connecting to ground through AC coupling. Could you try replacing R90 with a same footprint capacitor?

    Regards,

    Gautham Ramachandran

    Apps. Engineer- Haptics

  • 0 in reply to Gautham
    TI__Expert 3280 points
    Gautham,
    This is a follow up e2e chain from "How does supply voltage affect pwm input voltage for DRV8662" and is using it as in fig 35 of the DRV2700 datasheet.

    Rui,
    The configuration you mentioned is intended for the DRV2700 and not the DRV8662 as Gautham mentioned. In regards to your prior comments, since BST is not coming up then it would appear the part is damaged or the layout is not correct. Since this might take a few iterations of debug, allow me to message you through email so we can setup some time to talk on the phone.
  • 0 in reply to Gautham
    Prodigy 240 points

    Hi Gautham,

    Thanks for your reply. In my original schematics I had a capacitor where R90 is but I replaced it with a 0R resistor as I want to make sure that IN- stays below IN+.

    My original problem is that I want to drive an element (CMPB04) that has three therminals, GND, VCC and signal where signal is supposed to always be higher than GND. Rodney helped me with this in this thread. (see from my post from July 7). So the configuration I am trying to do is the one described in figure 35 in the DRV2700 datasheet. To my understanding, if I replace R90 with a capacitor OUT- may become higher than OUT+ which may cause permanent damage to the piezo bender. Can you see any other solution to my problem?

    Thanks!

  • 0 in reply to Rodney Miranda
    Prodigy 240 points
    Hi Rodney, a debug session over the phone sounds good. I tried to message you here on this forum but I couldn't find you. Can you please send me a message and I'll reply with my email. Thanks!
  • 0 in reply to Rui Chen58
    TI__Expert 3280 points
    Hey Rui,
    I wanted to post our results of our debug session to the forum. Based on the layout, there were two findings to prevent damage to the device.
    1. Move the feedback resistors closer to the FB pin to minimize the signal (VBST) to noise (L coupling) ratio, by only routing the VBST signal instead of the FB signal. For more information, see the layout section in the datasheet
    2. As a general practice, it is best to have decoupling capacitors for the supply as close to the pin as possible.

    I hope this helps. Let me know if you have any more questions.