Hi, I am new to kicad and I want some advices regarding my PCB. Can you please help me improve it ?
Here are some figure of the schematic and the PCB.
Add GND zone at top and connect all GND pins to it with vias.
Can you please show me an example ?
It would be helpful if I understood what this board is supposed to do…
But I notice several MOSFETs with (gate or source??) leads going out to a connector. (Are you calling MOSFETs U_ reference designation?)
Anyway…if the source or gate is left floating (connector disconnected) you run the risk of electrostatic discharge damage to MOSFET gate oxide. I think you ought to place protection zeners (maybe 7V5 or 8V2 rating)? gate-source to avoid damage when the connector is disconnected.
It is one 2 layer PCB I showed long time ago.
Compared to your PCB it is reversed. Connections at top (red), and continuous GND at bottom (blue).
At top there is also GND zone connected with bottom zone with vias. All vias at this picture are GND.
Having continuous GND is important from EMC point of view. I think it should be possible to have continuous GND at your PCB (it looks simple enough).
This circuit is used to charge a battery using a solar panel, discharge it via the different resistors that are connected to the mosfets (to simulate the different discharging process with diff resistors values) and to measure the charging and discharging current using shunt resistor and BQ Fuel Gauge.The mosfet are connected and controlled individually (one at a time) to discharge the battery! The U_ is automatically generated! The source is not left floating since all the sources pins will be connected to BAT- which is connected to the entry of the shunt resistor to measure the discharging current! and these mosfets are not working at the same time, only one of them will be controlled in case we want to discharge the battery and measure the discharging current!
I hope that it’s clear, please feel free to let me know if you still have difficulties understanding the circuit!
Ah do you mean that I need to add a vias (hole) to connect the 1st to the 2nd layer GND?
The schematic shows MOSFET gates connected through resistors to ground.
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That will require source lead being driven negative wrt ground in order to turn on the MOSFET. Are you doing that?
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This pcb layout view
seems to show the gates all connected together to a via to a track on the bottom of the pcb. So it appears that the schematic and the pcb layout do not agree. It APPEARS that you have your MOSFET pins assigned improperly. -
It would be helpful if I saw ref designations on the pcb layout.
These two views disagree with each other regarding the MOSFET connections. This is at least confusing if not a big error:
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MOSFET Gate-Source protection (zener diodes for example) needs to located on the same board as the MOSFETs, located as close to them as possible.
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@Piotr knows his stuff! The wise newbie will listen to him…
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A ground plane will cost you a few minutes of time and nothing else. It is unwise not to use one if you can easily do so.
Here is the PCB layout with references, I can’t see the ground! But I can see that one wire is going to the microcontroller (gate), the second one is going to the Bat + while the third one is going to the shunt resistor (to measure the current ) before we end up on the ground! Can you please point out where it that error ? I am really confused!
It’s that I don’t want to add a ground which will cost me a few minutes! I just want to understand the stuff!
I need to run. I might be able to respond more in 12 hours. I did not know that the black background view was reversed.
Is this bottom as viewed from the top? That adds to confusion, but it does not resolve the problems.
But still it does not make sense to me. The black background view looks like all MOSFET gates are connected together.
Yeah, actually the board is reversed! I started routing the bottom while the top has only few wires (red). Here’s the wires description :
They all have different gates with the same source and the same drain!! Unless if I am wrong!
You missed one sentence from my first post:
OP design is with SMD footprints at bottom.
No.
PCB 3D view was reversed to show bottom side.
But you asked to help improve PCB and at your PCB there are many pads not connected to GND yet.
It is hardly to believe that you really don’t see the connection lines we see at picture from your first post?
The easiest way to connect them is to add GND zone at top and connect them all to it by vias.
After it PCB will certainly be improved so it was my first advice.
You should place it at top because if you place it at bottom it will be divided by your tracks into many islands not having connection with each other.
I didn’t checked the datasheets but you probably are right. BobZ probably never designed pcb with smd elements at bottom (looking at pcb from top) what I have done many times.
I took a look at the schematic. I don’t know the BAT+ voltage.
If it is 1.5V then 47R 1W is OK. But if it is +12V than connected to it 47R will dissipate 3W.
I don’t see any 1W resistor at your PCB.
There is no idea to design PCB until you don’t have right footprints as changing them later means redesigning PCB because there can be not enough room for them.
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Thank you so much for your collaboration.
To be honest with you I still can’t see these unconnected pads… But I will add a gnd on the top, it should be on the second layer right (blue wires).
Yes you are right, actually, I will connect a 4.7V rechargeable battery to it which will allow the resistor to dissipate 0.53watt which is acceptable.
Do you mean that i need to change the footprint of my resistor to another one that has the dimensions of 1 watt resistor ?
Truly unbelievable.
Do you have a way to solder much bigger resistor at footprint of much smaller resistor?
