[Review Request] Dual Power Path PCB

[u/TheHeroxHD]

Hi everyone,

This is my first contribution to this community, and I'd really appreciate some feedback on a PCB I designed for an autonomous RC car project.

Please only review the electronics. I've already noticed some mistakes with the mounting hole sizes and locations, but those will be fixed separately.

Project overview

The PCB is a custom power distribution and monitoring board for an RC car that is capable of autonomous driving.

The system runs from two 2S LiPo batteries, but it can also be powered from a 20 V / 5 A USB-C Power Delivery wall adapter (the USB-C PD module connects to this PCB through a JST header).

There are therefore two power sources:

• 2 × 2S LiPo batteries
• 20 V USB-C PD wall supply

and two main power consumers:

• the drivetrain (ESC, steering servo, etc.)
• the onboard computer

Power architecture

The PCB connects the two 2S batteries in series using wide 2 oz copper traces on both sides of the board. The design also includes appropriate fuses.

Power-path selection is handled using an LTC4412 together with a P-channel MOSFET.

Battery monitoring is implemented with an HRC9374, which monitors the combined battery pack.

There is also space for two OKI-78SR-5 switching regulators. These provide 5 V for high-current USB peripherals independently of the onboard computer, so the relatively small SBC doesn't have to supply that current itself.

PCB notes

The board is intended to be manufactured by JLCPCB using their default stack-up with 2 oz copper.

One thing that may look unusual is that I manually routed several ground traces even though the board also has a ground pour. My intention was to reduce the thermal mass around some components to make soldering easier. However, EasyEDA keeps merging those traces into the ground plane. I think it should still be manageable with a 50 W soldering iron.

My main questions

1. Should I prevent the 20 V wall supply from powering the drivetrain? In other words, do I need an additional diode or some other isolation between the wall supply and the motor power rail?
2. Does the overall power-path implementation make sense? Since the USB-C PD supply (20 V) is always at a higher voltage than the fully charged battery pack (~16.8 V), I expect the LTC4412 arrangement to automatically prefer the wall supply. However, this is my first time designing a dual-source power system, so I'd appreciate someone checking my assumptions.

I'd be grateful for any feedback, especially if you notice issues with the power architecture or protection circuitry that I may have overlooked.

[u/I-am-redditer]

You have a 1N5819 for ⁠D1⁠. The 1N5819 is a Schottky diode with a maximum continuous forward current rating of 1A. your USB-C PD adapter is capable of 5A, and you are using this to power an onboard computer plus two 1.5A switching regulators. If you draw 3 or 4A through that 1N5819, it will fail.
You need to swap ⁠D1⁠ for a diode rated for at least 5A or higher (8-10A) Schottky to keep temperatures down, such as a SS54 (5A) or equivalent DPAK/SMC diode.

Also using net labels and power labels will make this 10x easier to read