Signal ground vs power ground for a microcontroller

Hi,

Referring here to www.roboteq.com/index.php/support/forum-...s/29526129-grounding and the user manual, what is the recommended way to isolate signal and power grounds?

I have a 24V battery system where battery power and ground go to the motor controller and are also used to power (via non-isolated DC/DC regulators) a microcontroller and other circuitry. If I were to connect to pin 15 for signal ground there would be a connection between B- and signal ground. Powering from the 5Vout is not an option.

Best Regards,
Evan

All devices, including your microcontroller, that shares a common power source with our controller should be isolated from our controllers IO port. There are two solutions:

1) Power your microcontroller using the 5v out from our power supply. Make sure you check the current draw of the microcontroller if you want to try this.

2) isolate all signals between the microcontroller and our IO port. In this case, I would recommend optical isolation.

Hi Gabriel,

Thanks for the quick reply. So, in order to do serial communication, I would need an optocoupler for TX and one for RX. For TX, I assume that would be between TX and GND on the optocoupler input side and between 5V and GND with a pulldown on the microcontroller side. For RX, it would be RX and GND on the microcontroller side, what would be the connections on the microcontroller side (VBAT and GND via a pulldown)?

Best Regards,
Evan

The pinouts you will need depends on your approach to isolation. We sell a Port Powered isoloator for RS232 on our webstore . That will not work for you unless you also adopt an RS232 interface.

OK, that won't work. What about a MAX3250? datasheets.maximintegrated.com/en/ds/MAX3250.pdf.

Also, I am looking to digitally switch PWR_CTRL. Our current design (for a competitors motor controller) uses a www.digikey.com/product-detail/en/nexper...27-2303-1-ND/5395605 to switch VBAT with a 100k pull-down. Will that same circuit work with your controller?

Finally, if I use one of the digital outputs to switch the motor brakes, do I need a back EMF diode for the brake coil?

Those components seem fine to me. I would try to test them first, but both look like they should work. We also recommend the sp3232e to do the TTL to rs232 conversion.

A feedback diode is recommend for all inductive loads on our digital outputs. Most electrical brake coils should come with one in the package. If you are using a drive package, I would check before you implement one yourself.

OK thanks, the SP3232e doesn't look like it isolates signal ground?

No it does not, you are correct.