DRV8823: DRV8823 mosfet switching time and blanking time question

Hi Henry3374,

On the DRV8823 datasheet there's a 3.75us blanking time.  From what I'm reading this means that the on board comparator ignores current readings for 3.75us.

The 3.75us is to account for inrush current of any capacitors connected to the outputs. During this 3.75us, the current can be higher than the Iocp max of 4.5A.

What is the behavior of the DRV8823 mosfets during this time?  The serial interface can operate at 16bits x 16mhz=1mhz so should be able to commanded to turn on/off in 1us which is faster than the blanking time.  Does the DRV8823 ignore all commands during the blanking time or is it only the on board comparator is ignored?

The serial interface continues operate. Any new commands are processed. Only the on board comparator is ignored.

We want to implement our own programmable blanking by using a comparator and switch the mosfets off at our own leisure.  Is this possible?

This is possible by disabling the current regulation. The VREF can be set to a voltage that would prevent the current regulation to begin.
Please keep in mind the overcurrent (OCP) circuit is still active. Any current above the Iocp for tocp will activate the overcurrent circuit.

What's the maximum speed the DRV8823 h-bridge can be switched from on to fast or slow decay?

If I understand the question, you would like to control the outputs being active and switching to fast or slow decay. Is that correct?
If yes, there are two limitations:
1) The serial interface will allow you to switch from outputs active to synchronous fast decay (set PH in the opposite direction) or asynchronous fast decay (set EN low).
2) There is no provision to enter slow decay using the serial interface.

The outputs will begin changing once the new command has been latched into the motor driver (SSTB pin rising or after 16 SCLK pulses if SSTB is tied high).