Protection Circuits for Input and Outputs on a PCB

Thread Starter

DJ_AA

Joined Aug 6, 2021
313
Hi

I am working on a PCB and would like to know if additional protection would be necessary for all my input and output ports.

All the ports eventually connect to a GPIO on my microcontroller.

These circuits that drive the ports.

Output port type 1
H-Bridge driver
1694430718899.png

Output port type 2

This is a load switch controlling 5V power to an external source or a relay, etc. The DC-DC that produces the 5V is rated to max 300mA
1694430790477.png

Input Port type 1

This input port use for external open-drain based signal outputs.
1694430948984.png
 

Irving

Joined Jan 30, 2016
4,049
Why are you making it so complicated? What are you trying to protect against?

The DRV8837 is an H-Bridge motor driver not an H-Bridge driver, the H & L designations make no sense. What are you trying to do with it?

A relay is, by definition, a galvanically-isolated output device... it needs no further 'protection' and a DC-DC converter is massive overkill. A simple BJT or 3v logic-level MOSFET driving the relay coil to ground, off the 5v rail, is all that is needed + a back-EMF diode.

1694438932896.png

The input port for an open drain output just needs a pull-up resistor, a series resistor and two TVS catch diodes. R5 may or may not be needed, depending on pull-up voltage.

1694439377481.png

Or if you are desperate for more isolation, try this:

1694440128135.png
 
Last edited:

Thread Starter

DJ_AA

Joined Aug 6, 2021
313
Hi

Generally, the protection is against over-current usage or any external shorts.

The DRV8837 is controlling some latching solenoids.

In regards to the input ports, this is just to give a level of protection, as there could be a possibility the input signal could be 5V.
 
Last edited:

Irving

Joined Jan 30, 2016
4,049
OK on the DRV8837 - that's a common use case, and makes sense if L & H refer to physical location...

Taking the relay output as an example, are you saying the relay is off board and you're worried about a short on the 5v rail to ground, external to the PCB?
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
313
OK on the DRV8837 - that's a common use case, and makes sense if L & H refer to physical location...

Taking the relay output as an example, are you saying the relay is off board and you're worried about a short on the 5v rail to ground, external to the PCB?
Yes, a user was connect ito GND in error or relay was to be faulty etc.

For the relay output I have I used a load switch as an additional option if I need power an external circuit with 5V. So it works as signal to a relay or to power any external circuit.
 

Thread Starter

DJ_AA

Joined Aug 6, 2021
313
The input port for an open drain output just needs a pull-up resistor, a series resistor and two TVS catch diodes. R5 may or may not be needed, depending on pull-up voltage.

View attachment 302546

Or if you are desperate for more isolation, try this:

View attachment 302548
Great, just to confirm can zener diodes be used or TVS i needed? Can this also protect against if 12V is connected to the input?
 
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