I’m working on designing my own Arduino Pro Mini PCB, and right now, I’m focusing on the power supply section. After some research, I’ve decided to use the MCP1700 voltage regulator for its low dropout and efficiency.
Before I move forward, I wanted to double-check my circuit. Does this setup look good for a stable 3.3V output? Are there any improvements or potential issues I should watch out for?
I’d appreciate any feedback or suggestions from the community!
If I recall correctly, you need a bypass cap for Vin. C6 should be closest to Vout or you change the characteristics. What do you have in mind regarding C5?
Edit: The recommendation from the MCP1700 datasheet is a 1uF ceramic for both Vin and Vout. What voltage will Vin be?
Thank You LarryD and ledsyn. Regarding my setup of cap I was looking for diagram from other topic on this forum - > Advices for powering my PCB circuit - #10 by ponpon777
I'd go with the manufacturers recommendation, that @LarryD showed you in #3. And you really should move C6 closest Vout. Why not get the datasheet, open it up and search for capacitor? You will find everything you need.
C5 could be nice to have if there's something that needs high current peaks, but if you design a micro, there won't be.
Consider adding a low voltage detect to your circuit it it will be doing anything critical or saving information in EEPROM, FLASH or FRAM. Your schematic skills look good. If you have the space double up on the electrolytic capacitors. When one fails you probably will not notice it unless it shorts.
Hi, in my case, I'll be using a LoRa module (Ebyte E220-900T22D) with a peak current of around 150 mA, connected to an Arduino 328 in a future project. Would you recommend keeping capacitor C5 in this scenario?
I've recently designed additional power supply circuit for an Arduino-based project incorporating a LoRa module, which can draw peak currents of approximately 150 mA. Initially, I considered using larger electrolytic capacitors (like 100 µF) on the output of my MCP1700 voltage regulator, but after revising the manufacturer's datasheet and guidelines, I've optimized the design.
The final version of the power supply circuit includes:
On the input side (VIN) of the MCP1700:
On the output side (VOUT) of the MCP1700:
This capacitor arrangement ensures stable regulator performance, adequately handles transient currents (up to 150 mA peak drawn by the LoRa module), and provides a clean, noise-free power source for the Arduino and its connected peripherals.
Feedback or additional suggestions are welcome!
I didn't find that number 150 mA, but the page is a mess. Tx power I found, 110 mA.. The power budget just got thinner for a MCP1700, 250 mA Output Current for Output
Voltages >= 2.5V, but it can do it. You chose 8MHz, 3.3V wisely, the power draw is much less than a 328P @ 16MHz, 5V.
I'm not sure. Regulators picks up voltage drop fast, on the other hand your LoRa could get sad and we wouldn't want that to happen. 
I tell you what, include it in the PCB design. You can always do some test runs w/o it, then solder it in place if it's needed.
That's a quite unorthodox design, noise from what?
For proper regulation, RAW must be at least 3.3+1 = 4.3V
Sorry, you're right—what I meant was that the 100 nF capacitor is intended as additional local filtering for the LoRa module. It will be placed as close as possible to the LoRa's power pins.
Thank You Jim-p for important info. I've just checked and actually, the MCP1700 regulator has a typical dropout voltage of around 178 mV at 150 mA load (according to the datasheet), so the minimum input voltage should be about 3.5 V to reliably maintain 3.3 V output—not necessarily 4.3 V?
How is dropout voltage defined in the data sheet?
Do you actually want to use the regulator if it is in dropout?
Are you looking at min and max values or just typical values?
Will it actually be in regulation?
Thanks for pointing that out! I checked the datasheet again, and you're absolutely right—I was looking at the typicaldropout voltage (~178 mV at 150 mA), but the maximum dropout voltage can be up to 350 mV.
This means that for a 3.3V output, the absolute minimum VIN should be:
3.3V + 350mV = 3.65V to ensure proper regulation in all cases????
So, while 3.5V might work under typical conditions, it's not guaranteed in worst-case scenarios. A safer minimum input voltage would be around 3.7V or more?
Electrical Characteristics: Unless otherwise specified, all limits are established for VIN = VR + 1V, ILOAD = 100 µA, COUT = 1 µF (X7R), CIN = 1 µF (X7R), TA = +25°C.
Those conditions apply to line/load/output regulation limits.
For Dropout Voltage (VIN-VOUT) the following footnote is cited
However, Vdropout is never defined. If you assume that Vdropout = VIN-VOUT then it makes no sense.
With confused specifications like that I personally would use a different regulator or if you are making just one PCB then buy several and test them.
If it's a module, wouldn't it be equipped with that already? A bigger cap to be a reserve would make more sense.
I've just wrote to ebyte - they recommend to add capacitor but they didn't mention about the value. I will let You know after their replay.
Developed version of your design
Two power lines for the LoRa and the 328P to minimize the LoRa's current peaks effect on the 328P.
What's the purpose of such capacitor? Filter, energy storage?
At least 4.3V if you plan on using that regulator
