Ground layout

[sabu31]

Dear All,

I want to know what is general practice for the layout of the ground path, particularly in two-layer boards, and if you don't have space for the uncut ground plane.

Basically, I a have microcontroller which gives PWM and senses signals through ADC. The PWM signals are around 100-150kHz. Now the ground pin is common. and Vcc is 3.3V. So how to should the ground be routed so that cross-talk is avoided or distortion is prevented in the adc sense signal?

Should there be separate ground paths for PWM and ADC signals which are then joined at the GND point of the microcontroller or what is best practice? I am attaching a generic diagram for understanding.

 

[mtwieg]

A lot of the suggestions found online about separating analog/digital circuits is impractical, especially with only two copper layers to work with. And usually deciding if and how to partition things requires a detailed description of how the board connects to all external circuits/systems (and how those circuits/systems are grounded and powered), not just a diagram of the circuits on the board.

So long as the PWM signals are not carrying much current, and the gate drivers are truly isolated, then they likely won't interfere with the ADCs. But again, discussing this usually requires much more detail.

 

[FvM]

You can be happy if you manage to get an almost continuous ground wiring. Separate analog ground might be feasible if the analog circuit exclusively occupies a zone on the board, otherwise I would put the requirement last.

A fragmented ground pour can be improved by jumper traces (or even jumper wires), marked light blue in the below example PCB.

You should be aware that a PCB without solid ground plane often fails EMI tests. In a power electronics application, switching noise from the power stage can propagate to the constrol circuit and e.g. cause processor malfunction and false switching.

 

[D.A.(Tony)Stewart]

Isolating power grounds depends on your decoupling at source so they do not share currents.
Here is one example, not the same as yours.

 

[sabu31]

You can be happy if you manage to get an almost continuous ground wiring. Separate analog ground might be feasible if the analog circuit exclusively occupies a zone on the board, otherwise I would put the requirement last.

A fragmented ground pour can be improved by jumper traces (or even jumper wires), marked light blue in the below example PCB.

View attachment 187174

You should be aware that a PCB without solid ground plane often fails EMI tests. In a power electronics application, switching noise from the power stage can propagate to the constrol circuit and e.g. cause processor malfunction and false switching.

So Generally are power electronics Board for commercial system typically four layer (except for low cost SMPS, etc). Also what is typically layer stacking

 

[D.A.(Tony)Stewart]

There are millions of SMPS and applications. Consider end-use and costs then analyze commercial products on your own.

Budget price 2 layers, complex motherboards 8+. STM32 boards USB? Microchip kits USB? So put SMPS on separate board with ultralow LDO after SMPS from any low voltage , learn Linear Tech , Analog Devices and TI , Power Design tools. TI shows PCB layouts too. Read Kit designs.

Master a simulator like Microcap 12. also LTspice.

 

[FvM]

So Generally are power electronics Board for commercial system typically four layer (except for low cost SMPS, etc). Also what is typically layer stacking

Yes. I'd consider four layer as a starting point. My preferred stack-up for medium complex control PCB is signal - gnd plane - shared signal and power - signal

 

[sabu31]

Yes. I'd consider four layer as a starting point. My preferred stack-up for medium complex control PCB is signal - gnd plane - shared signal and power - signal

If we keep power signal inside, how will it be able to carry high currents or applying tining to tracks

 

[FvM]

I was talking about control PCB, respectively control circuit part of PCB. Notice that your post #1 doesn't address power circuit, scope is uC + gate driver.

How to wire power circuit on PCB is a different question. Control circuit ground plane will usually not extent into power circuit, except perhaps for dedicated low voltage designs.

 

[sabu31]

I was talking about control PCB, respectively control circuit part of PCB. Notice that your post #1 doesn't address power circuit, scope is uC + gate driver.

How to wire power circuit on PCB is a different question. Control circuit ground plane will usually not extent into power circuit, except perhaps for dedicated low voltage designs.

Yes FvM, I asked more than scope of my 1st post. But what is your suggestion regarding stack up for Power Circuit. I

 

[FvM]

Power circuit can have current range of a few A up to several 100 A and voltage between a few V and several kV. Stack-up will be different in each case.

 

[D.A.(Tony)Stewart]

There is no general practice for Design.
It is your duty to specify the IO requirements for V, I and Tr risetime and # of nodes to connect with specs for crosstalk, thermal losses and controlled impedances.