It has been a while since the last post. There were delays in fabricating the final LPSU PCB design due to having 2 designs: 1 for flagship and another for 1 step below. The boards arrived last Friday. I was also busy with finalizing the USB2 Redriver board design.
New LPSU PCBs
The initial prototype PCBs were made by JLCPCB, but for the final product, I contacted a number of high-quality PCB manufacturers to make the board only. Unfortunately, the local PCB manufacturers are more expensive and some even refused to quote since I specified ENEPIG (gold plated) surface finish. I eventually selected a high-quality and expensive PCB maker. The whole process from quotation, design tweaks, and to getting the PCBs took almost two months.
LPSU already assembled is shown below. Please note that there is a rail not populated. There are two 12V rails, 5A and 3A. If CPU needs a dedicated rail, then the 12V 5A will go to the CPU while 12V 3A goes to ATX power connector. For motherboards with Intel SoC, there is no need for separate CPU power, hence only the 12V 5A is used into ATX power connector. The 12V 3A rail is left blank as shown in the pictures below.
I use regular diodes as rectifiers, not Schottky. It’s On Semiconductor MUR820G with Kemet 220pF MLCC next to it. This is an old but proven design preferred by Nelson Pass.
The smoothing caps are made-in-Japan Nichicon KW series; 2 x 10,000 uF for 3A rail and 2 x 15,000 uF for 5A rail.
After smoothing caps, it goes to WIMA Polyester caps (red in color, another 2 obscured) before voltage regulator (VR). The picture below is zoomed for better clarity in the next picture.
The picture below gives a better view of the caps used for VR. The second-stage VR output caps were obscured by the large smoothing caps. The small Nichicon fine gold cap is used for ripple rejection.
The picture below shows better view of the array of caps for VR input and output. All the reds are WIMA. The PC power supply supervisor IC was not yet populated while this picture was taken.
The brown color caps are Kemet tantalum used as VR output cap. They are expensive but take very little space, allowing smaller footprint PCB.
The picture below is the 5V LPSU VR board for SSD. I need to update this PCB so that it has 4 outputs instead of 3 shown below. No Kemet caps used here, only Nichicon fine gold caps and WIMA hidden (in between the fat Nichicon caps and Molex power connectors).
I was very excited in assembling Build 04 that I did not take any pictures after it was assembled in Streacom FC10. Right now I am breaking in Build 04.
USB2 Redriver
USB2 operates at high speed, max at 480 Mbps, hence there are many design rules which need to be followed. To give you a better idea of how the USB2 Redriver card looks like, here are the 3D rendering screenshots of almost final design. It needs to be fed with a low-noise 5V DC, already available from the LPSU board above.
Design a card also requires designing the PCIe bracket, even though this card does not use PCIe slot. Here are the pictures of the bracket. Due to low volume in initial production, the cost will be very high due to laser cut. Metal stamping can be used for final product but the minimum order quantity is high.
The design of this USB2 Redriver allows fine tuning of the boost (slight DC gain) and EQ done by the USB2 Redriver chip. The boost and EQ parameters are system dependent, like the length and quality of USB2 Audio cable used.
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