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2020/11/17 06:03:22
m_snaeem@hotmail.com
Hello,

I don't know whether this question is related to this forum or not. Sorry in the case if the forum is not right.
I want to design the PCB which has low power devices such as microcontroller USB-Uart converter and CAN controller which takes about 200mA current. and high Current buck converter which operates the Solenoid and consumes around 50-watt power. My question is should I have the same return ground on PCB or should I add a 0-ohm resistor/ Ferrite Bead to separate their return path near the input power connector. Can anybody suggest to me the correct grounding technique for the issue?
Actually, i have made common ground earlier but it did not allow me to enable the buck converter which is to be done from Microcontroller and enable signal get disappear and I can't turn on the buck converter.
2020/11/17 11:36:28
PStechPaul
There definitely needs to be separate grounds for analog and digital signals, and the power circuitry. They can be tied together at a single point as you propose. Also there needs to be adequate bypassing for each circuit, using a combination of small ceramic or film capacitors and larger electrolytics. Ground and power supply planes on the PCB are also helpful, but make sure the overall layout maintains proper spacing and isolation between high current and high voltage sections, and sensitive analog and digital signal paths.
2020/11/17 14:34:26
davea
definitely connect the 2 grounds at input power connector ground (maybe use multiple pins for ground)
high Current buck converter which operates the Solenoid and consumes around 50-watt power
this means that the input voltage is higher then the Solenoid voltage ??
 
is there 2 different voltages at the input power connector one each circuit ??
you need to give more details for good answer.....
 
 

Actually, i have made common ground earlier but it did not allow me to enable the buck converter which is to be done from Microcontroller and enable signal get disappear and I can't turn on the buck converter.

this sounds disturbing and may need to use a optocoupler to enable the buck converter
2020/11/17 14:43:56
oliverb
You'll probably need a 0R "resistor" due to the way PCB layout tools work, unless you want to hand-draw the entire ground. You can have different "nets" for high current and low current with different layout "rules", and the resistor forces a single interconnect point.
 
2020/11/17 15:37:46
davea
oliverb
You'll probably need a 0R "resistor" due to the way PCB layout tools work, unless you want to hand-draw the entire ground. You can have different "nets" for high current and low current with different layout "rules", and the resistor forces a single interconnect point.
 

good point...
but make sure you leave enough space around the part so at very end, you put a fat trace through it
or make a connection on the bottom side
also when you change sides with a hi current trace use 3 via's or a big pad 
2020/11/17 18:50:02
PStechPaul
I like to put a "test point" on the power, signal, and digital grounds, and connect them with a loop of bare wire. This provides a convenient point to connect the ground probe of a scope or DMM. In some cases I have used a low value resistor, such as 1 ohm for low current analog ground, and perhaps 10 mOhms for a 10-20 amp power ground feed. This can be used to measure the current.
2020/11/18 02:50:25
m_snaeem@hotmail.com
There is a 4 Pin connector with 24V, 12V, 5V and ground Pins. 12V and 5V need current in 100s of miliamps but 24V needs 2Ampere. So, may be as you guys suggested need 0Ohm resistor near power connector to separate 24V resturn from other voltages return.
2020/11/18 06:40:48
Mysil
Hi,
A 0Ohm resistor is not much different from a wire link or jumper.
It should have no electrical effect, and probably will not solve your problem by itself.
There are many other aspects of circuit design and board layout that may matter,
so whatever anyone say, there may be other members with different experience,
or opposing opinions.
 
While connecting digital ground, analog ground and high power ground together in a single point is a sensible practice.
Doing so at the Power connector may cause problems where control signals are connected to power switching components. Especially if there are long or complicated traces between power connector and power semiconductors.
Rather than at the power connector, you may try to connect digital Vss and high current return circuits together,
close to where Gate drive signals are are connected to power semiconductors.
And if this is all around in different places, you may have problems anyway.
Optical isolators, signal transformers, or proper FET driver IC components may help.
 
As mentioned above, 0Ohm resistor may be used to trick circuit modelling, circuit simulation, 
or board layout software by providing different names for parts of network.
 
It is also used to provide a link that may be removed or replaced to reconfigure a board. 
It is used in SMD circuit board production,
since it is a low cost component that can be mounted by the same pick and place machine that is used for other components. And thus can be mounted without manual work.
 
    Mysil
2020/11/18 17:03:42
davea
just make sure the low current GND side is the one that uses the 0 ohm res
and if the layout allows, use the switching supply GND as the only
path back to connector GND
Actually, i have made common ground earlier but it did not allow me to enable the buck converter which is to be done from Microcontroller and enable signal get disappear and I can't turn on the buck converter

has this been resolved 
 
 
 
2020/11/18 22:13:20
Beau Schwabe
I used to do IC layout for nearly 15 years and at the IC level, adding a resistor is commonly used to "trick" the tool by creating a Node separator so the tool can more easily work out the node paths for connectivity and simulation.  A common example is when A chip might have multiple Power supplies or multiple grounds.  Even the difference between an Analog ground and a Digital ground is done this way.
 
The main thing to keep in mind is that you don't want high current paths going  through or near sensitive circuits that would otherwise have low current through them.  For this reason you use a fan-out approach for both power and ground supplies from a central power point OR a power grid approach for a more even distribution across the entire design section if IR voltage drop is more of an issue.
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