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DRV8704: Mosfet switching proplem wrong order

Simon Walleczek
Prodigy 50 points
Part Number: DRV8704

Hallo,

Maybe you could help me I have a problem with the DRV8704.

To explain the problem let’s use this numeration for the Mosfet’s:

In the first Oscilloscope Picture you see on, CH 1 the signal on PIN INA1 , CH 2 the signal on PIN INA2, CH3 the signal on PIN A2HS , CH4 the signal on PIN A2LS . Let’s say PIN A2HS switch T1 and A2LS switch T4. This looks all fine in Picture the problem came now !

 

In The next Picture I measured the signal from the PIN A1HS on CH1, let’s say this is T3. All the other Channels measure the same signal like in picture one. The signal on INA1 and INA2 didn’t changed. On Pin INA2 there is still the PWM signal and the Signal on INA1 is still 0V .

I confriguated the DRV to force the slow decay mode so I wonder why does T3 turn on ?

According to the datasheet on page 12 the H-Bridge should be switch to High-Z when both input signal are Low ?

During the Measurement there was no over current event for the DRV and the second Channel were deactivated (BIN1 and BIN2 connected to GND).

Did you have any solution that T3 stay off ?.

  • 0
    TI__Genius 14487 points

    Hi Simon,

    It looks like you mixed up the FETs. This is how I understand what you told me above:

    You need to have A1HS and A1LS on one half bridge and A2HS and A2LS on the other half bridge. You can't switch them across the bridge like this.

  • 0 in reply to James Lockridge19
    Prodigy 50 points

    Sorry I have make an mistake in the Thread opening.

    In The first Oscilloscope Picture CH4 shows the signal on A1LS .

    A1LS is connected to T4.

    The physical conetion on the PCB looks like this :

    I have still the proplem that  T3 turns on when the H-Bridge should be in High-Z .

  • 0 in reply to Simon Walleczek
    TI__Genius 14487 points
    Simon,

    I have a couple questions:

    1) Do you experience this issue with the motor disconnected?

    2) Can you measure the gate of T3 and the AOUTx pin associated with it on the oscilloscope? The driver turns off the FET by shorting the xHSx pin and the xOUTx pin internally. This shorts the gate and source of the high-side FET which turns off the FET. If you measure the same voltage on those pins, the the high-side FET is off.
  • 0 in reply to James Lockridge19
    Prodigy 50 points
    Hi James,

    1) The issue don't experience when the motor is disconnected

    2) Thank you verry much. This was the solution, i measure the same Voltage on pin xOUTx :)

    So the Mosfet is definitely switched off. Now I must search why I have still problems to drive this motor. I thougth this was the reason

    Thanke you