First PCB design review/advice

[gautam023]

Hello everyone,

I am new to PCB design and would like to get some advice on my design. The project is a PDU using an LT3958 IC in SEPIC mode to get +15V and +5V from a 68V battery pack and LTC3630A in inverting mode to get -15V from the same battery pack.

I used only 2 layers for the design. Should I be using 4 layers or will 2 layers do just fine?

Design files are also attached here BMS_Power Supply4.zip . The software used is Eagle.

[robertferanec]

I am always careful, so my advice may be too safe: If you do not have experience with power supply design and you would need to pass EMC/EMI, then a 4 layer PCB may help. If you would have experience or if your product has to be super cheap, 2 layer PCB is usually fine but sometimes you may need to do some tweaking.

If you only need it for your own project (no EMC/EMI testing required), a two layer PCB will probably work ok.

[gautam023]

Thank you for your reply. I am not looking at the EMI levels of my design. Then looks like going with 2 layers looks good. And I would welcome any other advice on my device if you had a chance to look at my design.

[qdrives]

Just a few to start...

• Keep the switch nodes as small and short as possible.
• Place more Gnd via's, they are almost free. Like one for each component/pin.
• Perhaps more thermal relieves are needed. Keep copper balance to prevent tomb stoning.
• You can leave the polygon pour cutout. Clearances should take care of it.
• You have not provided schematic, so I cannot really check the circuit, but -15V seems wrong.
• Why did you go for SEPIC? if the input power is (way) higher, just go for buck - it is less problematic.

[gautam023]

The .sch and .pcb files are attached in a zip file in my msg under the name BMS_Power_Supply_4.zip.

As for why I went for SEPIC initially I wanted the same IC to do +15V,-15V,+5V and the only IC I found for all three with O/P was LT3958 and it has no buck configuration. +15V and -15V current requirements are just 100mA and SW voltage was high; hence had to change -15V IC and did not want to rework the entire design.

The -15V circuit is correct. It is according to the datasheet and I have cross-checked in LTspice.

[qdrives]

gautam023 Yes, sorry, I did not look in the zip.
And Altium importing Eagle design is not always nice. I know from experience.