Schematics help pls - Page 1
Forum section: electronics / general

author: Tavi
author_rank: Contributor
timestamp: November 24, 2021, 06:16:30 pm
content: I need some help with the below circuit (I know it is messy). The battery management circuit seems just fine but when I give power to the ME2108 and then to the AMS1117 the AMS1117 will heat up very fast so I think I have a short somewhere.Can you please give some quick ideas on what is going on? I did debugging for 2h but I'm not really an electrical engineer.Thanks!

author: daqq
author_rank: Super Contributor
timestamp: November 24, 2021, 06:56:55 pm
content: What's the input voltage and the current draw? Is +3V3 present on the output while it heats up? Could be completely fine - the AMS1117 is a linear regulator, which means that the excess voltage is simply 'dissipated' on the part. If you have, say a +5V input and a +3.3V output and you are using, say, 200mA, that means you have to dissipate 1.7V * 0.2A = 0.35W of power as heat - might not seem like much, but it is.

author: PlainName
author_rank: Super Contributor
timestamp: November 24, 2021, 07:14:13 pm
content: The ME2108 is a 2.7V device whereas the AMS1117 is 3.3v, so if there is any voltage on the AMS1117 Vout it's going to back-power the device. You need a diode between Vin and Vout to prevent that (shouldn't be a problem right now because there is nothing powering the 3.3V rail, but once it's running if the input power dies quicker than the output is consumed then you could have an issue).

author: PlainName
author_rank: Super Contributor
timestamp: November 24, 2021, 07:19:08 pm
content: And... I'm missing where the battery gets charged. There seems to be no connection between the charge chip and the battery.

author: Tavi
author_rank: Contributor
timestamp: November 24, 2021, 07:49:55 pm
content: @daqq Battery is lipo 3.7v 700mAh. Current draw is 200mAh max. Now it does not heat up at all and is pretty much dead (when it did heat up the ME2108 was outputting 2.7 ish - that is very strange).Something strange happened at some point either the ME2108 was super hot or the AMS1117 was super hot and then everything died.The battery management circuit works well still.

author: Tavi
author_rank: Contributor
timestamp: November 24, 2021, 08:15:25 pm
content: @dunkemhigh the AMS 1117 receives 5v and then it powers the esp32, there is a diode on the 5v boost converter is that it?

author: PlainName
author_rank: Super Contributor
timestamp: November 24, 2021, 08:23:19 pm
content: QuoteAs I noted, it's a 2.7V part so working perfectly. You probably want the ME2108A50PG instead.QuoteNo, that's for stopping the boosted voltage disappearing back down L1. The attached capture from the datasheet shows the correct position (D1 in this).

author: PlainName
author_rank: Super Contributor
timestamp: November 24, 2021, 08:27:36 pm
content: There is something off to the right which isn't shown on the schematic fully. That's connected to the 5V rail but presumably it's a sink?

author: Tavi
author_rank: Contributor
timestamp: November 24, 2021, 09:51:54 pm
content: @dunkemhigh is a dust sensor PM1.0 and PM2.5 that needs 5V.Before this I had the setup just like this one but without the boost converter and the step down converter on SMD, so I used these two modules and they where working absolutely fine (see the two pictures).I took a look atME2108and on the chip I can read the fallowing:2108A 1952/50.

author: PlainName
author_rank: Super Contributor
timestamp: November 25, 2021, 01:18:57 am
content: QuoteNo idea what that means, but could be OK. I was going from the schematic which says ME2108A27PG, and you can see from the datasheet clip that it ain't 5V. However, what it says on the schematic and what you place on the PCB aren't necessarily related! If you've bought the 5V version then that's what it should be.

author: Tavi
author_rank: Contributor
timestamp: November 25, 2021, 10:48:28 am
content: @dunkemhigh take a look at AMS1117 connections.... they are not goodI used an example from library in jlpcb software and it seems like the layout of pins is wrong .... now im 99% that is the issue with all this.In my schematic:1-VOUT2-ADJ/GND3-VINIn datasheet:1-ADJ/GND2-VOUT3-VIN

author: mariush
author_rank: Super Contributor
timestamp: November 25, 2021, 11:22:56 am
content: Just because nobody mentioned it.... 1117 is a jellybean component made by lots of companies, but it has a particularity as in SOME models oscillate and don't work right if the output capacitor ESR is not within some range, for example 0.2 ohm .. 1 ohmSo SOME models require an electrolytic capacitor or some other capacitor with enough ESR to be in that narrow range. Other models are "designed" to work with ceramic capacitors and don't require high ESR capacitors.A good 10uF <25v rated electrolytic may have an ESR value higher than 1 ohm.For example, Panasonic FC series peaks at 2 ohm esr for 10uF electrolytic capacitors :https://industrial.panasonic.com/cdbs/www-data/pdf/RDF0000/ABA0000C1209.pdf10uF 25v rated has 2 ohm esr, but 10uF 50v rated is 1.3vRubyzon ZL is better at 0.96 ohm for the 35v rated version, 0.5 ohm for the 50v rated one :https://www.rubycon.co.jp/wp-content/uploads/catalog-aluminum/ZL.pdfSo I'd say if you do have to use electrolytic capacitor, go up in capacitance a bit ... a 47uF 16-25v rated capacitor would have around 0.2...0.5 ohm esrAlternatively just use a polymer / solid capacitor in series with a 0.2ohm resistor.OR use a different linear regulator that you know for sure it doesn't have instability with capacitor choice.