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Trouble with DKD8332: FETs always remain active

Jaime Boal
Prodigy 50 points

Hi everyone!

I am trying to control a BLDC motor using the DKD8332. However, two of the three FET pairs of the bridge remain always active, which results in a short circuit between PVDD_X and GND_X. The short cirtcuit persists even when the device is not connected! I have checked the control signals that activate the gates and they seem to match those of the datasheet. Any clue of what might be happening? Have I damaged the component even though it did not become hot? In the latter case, what could be the cause?

I would really appreciate any guidance that you can provide me. Thanks in advance.

  • 0
    TI__Guru 55615 points

    Jaime,

    Something is definately not normal here.  Are you sure the device is installed correctly on your PCB?

    Please see page 27 in the datasheet.  The pin one indicator (small, lightly marked white dot) on the top of the package corresponds to pin 1.  I ask this since it is a common problem. 

    The device has a single input for each half-bridge and dead-time protection is built in.  It is not possible (without some device damage) to enable BOTH of the FETs in the half-bridge.

     

  • 0 in reply to Ryan Kehr
    Prodigy 50 points

    Ryan,

    Thanks for your quick reply, but I had soldered the component correctly, the problem must be elsewhere. Let me explain the problem in more detail, as I have been carrying out several test over the last few days.

    I have ensured that the control signals for the MOSFET gates match those of the datasheet for all possible values of the Hall sensors, and I have checked that there are no shortcuts before connecting the device.

    The next step was to actually connect the motor windings and power the system up. To keep on the safe side PVDD was set to 18 V (the current was limited to 2.5 A in the voltage source) and GVDD to 12 V. The motor did not respond in this state, so just to check I made it slightly turn manually. The driver immediately started to draw the maximum possible current (i.e. 2.5 A) and the motor did not even move. I quickly turned the power off and checked the outputs. OUT_A is in shortcut with both PVDD and GND which leads me to think that both the high and low FETs always remain open (and are therefore permanently damaged).

    The only possible problem I can figure out is that the motor windings may not be connected in the correct sequence. However, as the device is protected, this should not affect. Am I right?

    In case it is a hardware design problem, permit me to briefly explain how everything is connected. I have implemented the minimum working circuit displayed on the first page of the datasheet (i.e. the BST capacitors, the VREG capacitor, and a 39k resistor to provide the current limit reference). Should I solder all the noise suppression capacitors too even though for the test I am using a single motor and the voltage sources already go through a series of filters before actually entering the device?

    Thanks in advance for your help,

    Jaime

  • 0 in reply to Jaime Boal
    TI__Guru 55615 points

    Jaime,

    The schematic on the front page is a "simplified" schematic and just meant to show basic hookup.  I highly recommed you start fresh with a new unit and use the schematic in figure 8 of the datasheet.  "Loc" in series with the motor is not really necessary at 18V PVDD, but the rest is. 

    Without the 100nF capacitors as close as possible to the supply pins, it is possible that high voltage spikes are killing the driver.  Local decoupling is critical to proper operation of the device.