DRV8886AT: Holding device in sleep at power up

Hi Matthew,

Referring to the datasheet section 7.4, there is a note to hold STEP low while coming out of nSLEEP or when applying power. The question would be does STEP need to be held low while the device is in the SLEEP state, or can the device be powered up into SLEEP mode?

Please note the last sentence on page 14 of the datasheet.

"On power-up or when exiting sleep mode, keep the STEP pin logic low, otherwise the indexer advances one step."  This is the reason to hold STEP low when exiting sleep mode.

When in sleep mode, it is recommended to hold any input with any internal pulldown low to reduce power consumption.

In this same section there is also a note that says tSLEEP must elapse after falling edge on the nSLEEP pin. This makes  me think that holding the nSLEEP pin low during power up would not keep the device in sleep since it is waiting for a falling edge?

The device will enter sleep mode if nSLEEP is low as stated in the Pin Functions Description. The note applies to when the device is already awake and entering sleep mode.

In my situation, STEP is tied to MCU so it can be held low for steady state, but the power on sequence might be unknown. Motor driver gets power from a source that is expected to reach steady state before MCU gets its power source, but otherwise the full board gets power at the same time.

1) Are there any problems with having activity on the STEP pin while the device is in SLEEP?

There are no problems. There is just a small amount of wasted power due to the internal pulldown resistor. This is true for any of the inputs with internal pulldowns.

2) Can the device immediately go into SLEEP at power on, preventing any errors from having the STEP pin not being held low?

Yes, the device typically enters sleep mode when powered up. FYI -- the GPIO pins of many mcus default to when reset. The internal pulldown on the nSLEEP pin is intended to keep the DRV8886AT in sleep mode until it is commanded to exit.