Not sure you can do that - the Si9886 requires all its inputs be no lower than -0.3V w.r.t. its ground terminal - you areproposing low-side switching of the Si9886 - its ground will then rise to Vbat, so that Arduino ground will appear as-Vbatt. If any of the Arduino pins connected to it are driven LOW, or if the Arduino is powered down you'll fry theH-bridge inputs.The normal approach is high-side switching - what is Vbatt? If its also 5V then a logic-level p-channel MOSFET could be used to switch the H-bridge (if higher you'd need an small n-channel MOSFET as a level-shifter to drive the p-channel gate.What state will the Arduino be in when sleeping - can it drive an output HIGH or LOW then?BTW the H-bridge has a standby current drain of about 75uA, not 300uA - see the graphs in the datasheet. The300uA figure is across all supply voltages and temperatures.
The best alternative would be an H-bridge that uses low quiescent current, but I don't know how you'd even go about searching for one.
5 volt system. An atmega328P-AU, DS3234, & h-bridge (Si9986)My atmega will be sleeping, waiting for the interrupt from the DS3234 timer. DS3234 will have Vcc cut off from an Arduino pin, so it runs on Vbatt. But if I'm reading the datasheet correctly on the Si9886, it uses 300 uA in standby mode.
Low-side switching to turn the power supply to the H-bridge off using an N-channel mosfet is OK provided you set INA and INB high first. Similarly, turn the mosfet on before you set the pins driving INA and INB to be outputs.