How we can charge a 5V device monitoring the input voltage in real time - Page 1
Forum section: electronics / projects

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 10:36:52 am
content: We have made a PCB using a MIC2876 to boost a 2.5V/4.5V 0.5 A input voltage to 5V output to be able to feed any device connected to two USB ports (USB-C and USB-A.)We've also implemented a current sensor connected to an LED strip to monitor the incoming energy level.We tested the unit by applying an input voltage in the range of 2.5V to 4.5V 0.5A but instead of boosting to 5V the output voltage is the same as the input - it fails its purpose.We have tried to replace the IC and also built other PCBs but with the same result. We also tried to remove the current sensor to make sure it was not producing an excessive resistance, drawing all the incoming current but that didn't help, either.Do you have any idea of what could cause the malfunction and do you have any suggestion to improve, if possible, the design?

author: todorp
author_rank: Regular Contributor
timestamp: December 13, 2021, 10:48:02 am
content: I don't know it this is the problem but in the MIC2876 datasheet example (page 2) OUTS pin is connected directly to OUT pin...

author: gamalot
author_rank: Super Contributor
timestamp: December 13, 2021, 11:11:21 am
content: When you say "applying an input voltage in the range of 2.5V to 4.5V 0.5A", you mean that the power supply you are using has current limitation or overcurrent protection, right? Have you tried to increase the current limit?

author: gamalot
author_rank: Super Contributor
timestamp: December 13, 2021, 11:14:26 am
content: Quote from: todorp on December 13, 2021, 10:48:02 amWhat you see is a reference design of a fixed output voltage models.

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 11:19:04 am
content: We try to increase the current range between 0.5A to 2A but the result is the same, the IC output is the same as the input

author: Ice-Tea
author_rank: Super Contributor
timestamp: December 13, 2021, 12:11:33 pm
content: Points to the bypass mode being activated? "The MIC2876 automatically operates in bypass mode when the input voltage is higher than the target output voltage. In bypass mode, the NMOS is turned off while the PMOS is fully turned on to provide a very low impedance path from IN to OUT."Have you checked the values of the feedback resistors? And the voltage at the FB node?

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 12:50:20 pm
content: Hi Ice-Tea, thanks for your input but our feedback resistors are the same values ​​as in the datasheet

author: Avelino Sampaio
author_rank: Frequent Contributor
timestamp: December 13, 2021, 01:38:23 pm
content: TestTestPlease, confirm for us if your chip code contains the letter "A". Example:MIC2876-AYMT-T5

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 01:46:53 pm
content: Hi AvelinoWe used MIC2876-5.25YMT-TR

author: nali
author_rank: Frequent Contributor
timestamp: December 13, 2021, 02:11:40 pm
content: So as already mentioned above looks like you're using the fixed output device with the reference design for the adjustable version.Try removing R12 and replacing R11 with either an 0R or as low as possible value.

author: Ice-Tea
author_rank: Super Contributor
timestamp: December 13, 2021, 02:12:50 pm
content: So, that's a non-adjustable version where you need to connect the FB pin directly to Vout (and that will regulate to 5.25V).

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 02:30:32 pm
content: now that I don't use the variable version I remove the resistors(R11 and R12) and short outs and out, but I still have the same problem

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 13, 2021, 07:33:02 pm
content: This might sound silly but happens: Are you sure the ic orientation is correct?Could you post a a picture of the the pcb section of the MIC2876? (Design picture and real picture)

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 10:52:25 pm
content: Hi DavidI attach the images[ Specified attachment is not available ]

author: testtest
author_rank: Contributor
timestamp: December 13, 2021, 10:54:23 pm
content: And the other ones

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 14, 2021, 02:29:30 am
content: I see weird copper traces in a lot of smd pads.Is that an artifact caused by the gerber viewer?Make some connectivity checks...

author: nali
author_rank: Frequent Contributor
timestamp: December 14, 2021, 09:39:19 am
content: My guess is it's oscillating, if it's doing anything at all. For example that looks like a *really* long GND path for the decoupling caps C1 & C8. If the artifacts David mentioned are actually there maybe it's an out-of-date copper pour?

author: tooki
author_rank: Super Contributor
timestamp: December 14, 2021, 05:48:48 pm
content: Quote from: DavidAlfa on December 14, 2021, 02:29:30 amThat looks like Altium (and not its Gerber viewer), in which case that’s bad news.After my first pour screw up, I set Altium to always update pours.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 14, 2021, 08:22:00 pm
content: Doesn't Altium run connectivity checks when exporting the gerbers to ensure everything is correct?Should have spotted that huge mess up.

author: testtest
author_rank: Contributor
timestamp: December 14, 2021, 08:56:20 pm
content: Thanks for your input but before generating the gerber file, drc was done

author: testtest
author_rank: Contributor
timestamp: December 14, 2021, 09:01:02 pm
content: if it can help here are the gerber files

author: testtest
author_rank: Contributor
timestamp: December 14, 2021, 09:03:43 pm
content: This is a file where you can see the complete design that the machine sees when making the tile. Like this

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 14, 2021, 10:37:28 pm
content: Looks ok in the gerbers...So have you:- Ensured there're no shorts, specially under the QFN package?- Shorted U1, pins 1-3,?- Shorted R11?- Connected a slightly higher voltage than Vmin, ex. 3V at VIN?What are you getting at the output?Have you checked SW with a scope to see if it's doing something?

author: testtest
author_rank: Contributor
timestamp: December 15, 2021, 11:25:09 am
content: Hi DavidWe have test all the part in your list and they seems fineregarding the last 2 questions:What are you getting at the output? the voltage output is exactly the same as the input, like is bypassing the ICHave you checked SW with a scope to see if it's doing something? We are trying to find someone with an oscilloscope

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 15, 2021, 02:42:58 pm
content: Are you sure you got the fixed voltage version?The datasheet isn't clear about the markings.Vref is 0.9V in the adjustable version, it would explain why it bypasses the input.Is the same happening when using the resistor feedback to OUTS pin?Have you thoroughly checked their values?Edit: The old Micrel datasheet is complete:https://dtsheet.com/doc/1341016/mic2876---micrel76H = Fixed 5.25Vout

author: testtest
author_rank: Contributor
timestamp: December 22, 2021, 10:49:13 pm
content: Hi, sorry to keep you waiting but the engineer was running additional tests with better equipment: the result is the voltage is equal to the input and the IC does not work at 2mhz or that the oscilloscope did not read any frequency

author: testtest
author_rank: Contributor
timestamp: December 22, 2021, 10:50:18 pm
content: Hi, sorry to keep you waiting but the engineer was running additional tests with better equipment: the result is the voltage is equal to the input and the IC does not work at 2mhz or that the oscilloscope did not read any frequency

author: testtest
author_rank: Contributor
timestamp: December 22, 2021, 11:07:16 pm
content: Hi, sorry to keep you waiting but the engineer was running additional tests with better equipment: the result is the voltage is equal to the input and the IC does not work at 2mhz or that the oscilloscope did not read any frequency

author: testtest
author_rank: Contributor
timestamp: January 21, 2022, 01:31:56 pm
content: Hi everybody,sorry for the late response but we had a lot of trouble during testing so we have to undergo few twice with different tools.At the end the main problem was that we took reference schematic which is for variable volatge IC, while fixed version was soldered.Some of you spot the problem immediately but when we undergo troubleshooting purchasing a variable IC version and soldering on the board the issue remain (probably because our tool could not control the heat used during the soldering process)My mistake was also not providing this forum with the BOM list, it will probably lead immediatly to the real problem and make it unquestionable.Now we are going to change the configuration to support the fixed version and also we will place the input capacitors closer to the IC to reduce the noise.My apologies again for the time you loose and my compliment for your efficiency in spotting the root cause almost at once.My regardsAndrea Poma