Dear all,
I’m a bit confused about protection against back EMF / inductive kick-back when using the DRV8838 carrier board, it looks like the DRV8838 IC itself does not have any clamping/flyback-diodes. Is the idea here that the reverse-protection circuit on the carrier board (Q1, D1, R1) also protects against these voltage spikes?
Maybe this is a stupid question but since words like “back EMF” aren’t even mentioned in the production description I was a bit worried…
The reason I’d love to have a clarification here is that I use a quite expensive ARM System-on-Module to control the motor and I would really like to not destroy it 
Both the motor and the SoM are powered directly from the same Lipo battery, and the SoM has an absolute maximum rating of 4.8V on the power supply, so there is not much room for error here…
Thanks a lot for your help!
Michael
The body diodes of the H-bridge MOSFETs suppress inductive kickback.
If using the motor power source to also power the CPU, include adequate decoupling circuitry (an RC filter at the very least) in the power connection to the CPU.
This is an advanced topic, so if you are a beginner, expect difficulties with this approach. You really need an oscilloscope to characterize the electrical noise levels, as each setup is unique.
Thanks for your help Jim!
Am I correct in thinking then that back-emf protection is (mostly?) provided by the MOSFET diodes and bulk capacitance, and the reverse-voltage circuitry (Q1, D1, R1) does not really help here? This is somewhat the origin of my question: I was just confused why this reverse-voltage protection is there, as I have never seen this used in another motor driver application.
Concerning noise level: I’ll probably just test and see what happens, as long as I’m somewhat convinced these tests won’t destroy the System-on-Module There is quite a lot of bulk and filtering capacitance on my custom carrier board, and also the SoM has its own additional filtering and voltage regulation, so maybe I’m fine here (the SoM’s datasheet just advises to “avoid excessive ripple or glitches” so that sounds pretty robust Plus, the motor I use is very small)
Best
Michael
To help prevent destruction caused by incorrectly connecting the power supply to the board.
Doesn’t sound robust to me. What is “excessive”?
A minimal example of a power supply decoupling filter for a CPU board might be a 10-47 Ohm resistor in series with the positive motor power supply lead, followed by a 100 uF cap to ground. In general the larger the resistor, the better, but it must be chosen consistent with the current draw and input voltage requirements of the uP board.
Google “power supply decoupling” for more info.
