DRV8837 and Back EMF MCU Resetting

Hello,

I designed a systems which will going to drive 16 DC motors. I have 16 drv8837, a dc to dc converter, MCU and RS485 driver.

My DC motors characteristics is like below:
http://www.roboweb.net/rw-ml-1343.html

My problem is when i try to start 3 of DC motors at the same time my MCU's power get lost for 100ms duration. I think DC motors are consumint all power of my caps in pcb include MCU's power caps.


That is why i go further in my test and try to add delays between start time of DC motors. it can drive up to 4 DC motors if i put 10ms delays betweeen start times. This makes me think about BEMF.

I decease my input power 8V to 6V problem increases. If i increase input power 8V to 9V poblem decreases but not removed and also my DC motors consume more current and 9V is the absoulte maximum voltage of my DC motors.

I am driving DC motors in clock-wise and counter clock-wise thats why i can not add schocht diode to DC motors pins.

Let me share you my power stage.



i replace feritebead with schotchy diode but problem still continues.

Can 4dc motors cause voltage drop at power stage? I thought DRV8837 can handle BEMF.

Now i am thinking about design ne  PCB and seperate ground planes of MCU and motors, also add soft start circuit to DC motors but can i try anything else before this looong step =).

Can you suggest me anything that can cause a soft start? I am also thinking about adding an inductor series to DC Motor.


Thank you for your help.

Other Screenshots from my design.