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Switch off motor driver A4988

allen25

Apr 1, 2024
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Hello, Now that I have my circuit (for the roller blind drive) in operation and was able to see how far the circuit can get by with the battery power, I had to look again. 10 days isn't bad, but I actually think it's a bit short. So I started doing the math and looking at what the A4988 needed. So I discovered in the Pololu data sheet that it can require a good 4 to 8mA, even though the outputs are switched off. That's pretty much how it could work out. Converted per hour, I got about 8.6mA for the entire circuit with µC and driver. If I subtract 2mA for the ATmega328 and the voltage regulation (it's definitely a bit high) then I stay at around 6.5mA. If I now subtract something for the stepper motor, since it also runs every now and then (not for long and often), then I estimate that there will be around 4mA left over, which will go to waste. So I want to turn that off. I always have the A4988 with Enable on LOW and Sleep on LOW when I don't need the motor. Now I thought I could switch off the logic voltage of the A4988 to be really economical and only supply the A4988 with 5V when I need the motor. Now my question is whether there are concerns here because the 12V motor voltage would remain applied to the A4988. Or would you rather leave the logic voltage connected and use the enable input of the A4988?
 

Martaine2005

May 12, 2015
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Don’t be concerned. If as you say “12V at the motor”, if the motor isn’t running, there is no waste.
Trying to be frugal with 4mA is unnecessary.
 

Harald Kapp

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Nov 17, 2011
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my question is whether there are concerns here
Yes, but not with regard to the 12 V, the chip should be able to manage that part.
Butturning off the logic supply voltage will turn on the protection diodes on the logic inputs and will power the chip via these diodes. This mode of operation is not defined and unexpected things may happen. From the motor turning randomly to the driver chip becoming defective.

The chip itself should draw only 10 µA wehn in sleep mode:
1712915968520.png
Your observed 4 mA are sourced by another part of the driver module.. You'll have to locate that part to find a remedy.
 
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