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DRV8701 PWM truth table question

Glenn Monroe
Intellectual 330 points
Other Parts Discussed in Thread: DRV8701, UCC27201, DRV8711, DRV8412, DRV8844, DRV8881

In the specification for the DRV8701 Table 2 on page 14 shows the output configuration for a variety of input conditions.  It shows the eventual result at the output of the external FETs as opposed to the output of the DRV8701.  My intention is to use the part to drive two half bridges separately as opposed to always being in a full H-bridge mode.  If I walk through the table it appears that I can get every combination of outputs I also need a combination of inputs where SH1 and SH2 will both be on.

If I look at the table it appears that I would need both IN1 and IN2 to be low for that condition.  However, it lists the output of the FETs as high-Z.  What are the gate voltages doing at that point?  Are they all low?

  • 0
    TI__Guru** 114905 points
    Hi Glenn,

    There is no condition that allows both high sides to be active simultaneously.

    Perhaps we can point you to a different device that needs your needs. What are your voltage and current requirements?
  • 0 in reply to Rick Duncan
    Intellectual 330 points

    Input is 12V nominal with a max of 14.5V. I would like to power driver and FET drain from same supply.

    Ideal setup would involve four separate FET drives or two separate half bridges.  I was looking at the UCC27201 but was steered away by a TI FAE. He never explained why UT wasn't a good choice.

  • 0 in reply to Glenn Monroe
    TI__Guru** 114905 points
    Hi Glenn,

    It may be because of the absolute maximum voltage if you are trying to use the same voltage for driver and FET drain. Voltage spikes could exceed 20V.

    You did not mention current requirements.

    For high current, the DRV8711 may fit your needs. Although listed as a stepper driver, it can be used to control two full bridges in PWM mode. It is similar to putting two DRV8701 together.

    If the current is lower than 7A, an integrated device may meet your needs. There are several available, such as the DRV8412 and DRV8844, and the DRV8881. You would determine if they fit.

    Many of the DRV8x devices have current regulation built in. Once the current exceeds a threshold, the outputs can switch to attempt to limit the current. This may present a problem for your application.