[PCB review request] Pi zero breakout for sensors + 3-30V regulated input - Page 1
Forum section: electronics / beginners

author: mrburns
author_rank: Contributor
timestamp: July 15, 2023, 02:50:27 pm
content: Hi, I could use some help with my hobby PCB design. There must be tons of rookie mistakes and other things to improve. This board is for Raspberry Pi Zero W and acts as a breakout for sensor modules. Mainly DHT22:s. The power will be delivered from battery or usb. I used Altium Circuitmaker2 for this project.▶ I used TIs online power designer to get the power delivery circuit I wanted. This one uses TI TPS55289 buck-boost regulator and takes 3-30 VIN and outputs 5V 500mA max. (avg usage will be 150-250mA). After the regulator the 5V goes to the PIs 5V pin and to the LM1117MP-3.3 linear regulator to feed the 3.3V to the sensors. I did not want to use the PIs 3.3v for possibly 20 sensors.▶ The GND is poured to the top and bottom and I already added lots of vias. Im little unsure of are the vias 'correct' size. I think I will order the PCBs from pcbway.com with SMD components assembled. pcbway website says that they require annular ring size of 6mil. They also state that all vias should be same size on the pcb. my Vias are 18mil diameter and 12mil hole size. Should I use smaller hole size? If the hole size is 6mil and the diameter is 18mil then the annular ring is 6mil right? There was no way to check the annular ring or add design rule on circuitmaker2.▶ The TPS55289 regulator has vias on its traces on the reference designs for heat dissipation and better grounding so the 18mil diameter was the largest I could fit in the design.▶ The reference design of the TPS55289 also showed and stated that there should be some separation between the AGND and PGND so I think I managed to copy the idea of the reference design.▶ The voltage to the sensors is selectable between 3.3V and 5V with jumper. I think this design of mine should also bee looked at. The ouput of the LM1117 regulator is disconnected from the sensor voltage line by NPN transistor if the 5V is selected to protect the regulator. Is this even necessary? I did not use diode because I did not want any voltage drop.▶ I have no idea if the mounting holes are correct and if there is some standard to them.▶ I will order the PCB with all SMD components assembled.SincerelyNot electrical engineer. (actually automation engineer) (▀̿Ĺ̯▀̿ ̿)Link to the project on altium365: ↓https://365.altium.com/files/F83B14F7-4F95-4AAD-81B0-549B5C326031Link to all files:↓https://1drv.ms/f/s!AnfIOtcTpP6BgrIedCTnukogk8Dn7w?e=TQX36dLink to TPS55289 pdf:↓https://www.ti.com/lit/ds/symlink/tps55289.pdf?ts=1689073822212&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS55289

author: dobsonr741
author_rank: Frequent Contributor
timestamp: July 15, 2023, 04:18:43 pm
content: Gut reaction: the TPS55289 is an overkill. Also: are you OK soldering it?

author: mrburns
author_rank: Contributor
timestamp: July 15, 2023, 04:30:50 pm
content: I will order the PCB with all SMD components assembled.I also like the versatility of the TPS55289. If I someday need to modify the design for 24V-out it should be quite simple.The I²C interface on the chip is also one thing Im looking forward to test out and play with.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: July 15, 2023, 07:29:18 pm
content: It seems the I2C is the only way to configure the output voltage. How are you going to set it to 5V to boot the raspi up?

author: mrburns
author_rank: Contributor
timestamp: July 15, 2023, 08:47:53 pm
content: Good point. I was under impression that using the TI power designer with 3-30VIN and 5VOUT 0.5A would give a schematic that would give 5VOUT by default but now Im not sure abouth that. In the schematic the VCC of the regulator is connected to EXTVCC so it gives 5V reference? If needed I can use any of my RPIs to set the registers to output 5V through the I²C interface.If it is the case that the registers are volatile and the ouput would need to be set every time it boots up then this would be a problem and I need to change the chip.

author: liaifat85
author_rank: Regular Contributor
timestamp: July 17, 2023, 11:23:03 am
content: The vias you've used (18mil diameter, 12mil hole size) are generally suitable for most PCB manufacturing processes. However, since you plan to order from pcbway.com, and they require an annular ring size of 6mil, you should adjust your via hole size accordingly. To achieve a 6mil annular ring with an 18mil via diameter, you would need a hole size of 6mil. So, you can change the hole size to 6mil while keeping the diameter at 18mil. Having consistent via sizes throughout the PCB is good practice and helps with manufacturing.There are other designs at PCBway website faetureing Raspberry Pi zero like this:https://www.pcbway.com/project/shareproject/PiPod___Raspberry_pi_Zero_portable_music_player.htmlIf you have any dilemma, you can see these designs or ask their customer service engineers by mail.