TCA6416A: Input Level at POR / pull-up resistor value

Hello Ueli,

The device port pins starts up as a hi-z (tri state). I recommend tying either a pull up or down resistor on the ports as it is not a good idea to leave hi z inputs floating.

Thanks,

-Bobby

Hey Daniel,

"Does this mean, that I can connect two ports of the TCA6416A to the M0/APHASE and M1 ports of the DRV8834 and set all different states (high, low, tri-state)?"

So I am not an expert on the DRV8834 but I can give you my thoughts/comments.

I glanced over the device and saw that you use M0/M1 to set the step size so setting the P Port of the TCA6416A high or low will set most of it. I am unsure how the device knows whether the input is HI-Z or not though... According to table 7.5 the ViL is 0.7V max and ViH is 2V minimum. I am wondering if the input is edge rate triggered or if it uses the inbetween voltage of 0.7V and 2V as a Hi-Z where internally they have a weak current source (back biasing prevented with a diode) feeding into the internal pull down resistor to generate a voltage between the two thresholds.

Either way I would double check with the TI team responsible for DRV8834. My thought is that our device should work though.

"So tri-state is not only possible after POR but also during operation by setting to the TCA6416A port to input?"

Yes, this is correct. Please note though that M0/APHASE of the DRV has an internal pull down resistor so at start up and when set as an input, the P Port will be referenced to GND through the internal pull down on DRV's M0/APHASE pin. (This is fine/good for our device)

"This way I could set all possible step sizes in the indexer mode of the DRV8834. Is this correct?"

From what I can see, yes. Please double check with the team responsible for DRV8834 (just make an e2e post asking about that device). In particular, how does the device input determine the input is Hi-Z? I'd be interested in knowing this too. (If you find out, let me know!)

Thanks,

-Bobby