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[disclaimer - I am new in DIY and this is the first PCB I designed myself]

I designed a PCB for a very simple ESP8266 12-F + RGB LEDs project.

I assume that I am doing something fundamentally wrong because the voltage regulator is connected to a 5.1..5.4 V, 500 mA supply but outputs 4.4 V instead of 3.3 V.

Note that the AMS1117-3.3 regulator uses the tab as another VOUT.

Note also that only the power-supply, the capacitors, and the regulator are currently mounted to the board. The ESP and LEDs are not yet on the board.

For details check the schematics screenshots below:

enter image description here

enter image description here enter image description here

Any hint/help is highly appreciated!

EDIT: I am terribly sorry, just noticed that the actual design which was printed indeed was using the full-copper approach:

enter image description here enter image description here

UPDATE: In the meanwhile my ordered 22uF smd tantalum capacitors arrived and I did some experiments:

  • 22 uF capacitor without resistor -> 4.34 V
  • 22 uF capacitor + 330 ohm resistor -> 4.22 V
  • 22 uF capacitor + 100 ohm resistor -> 4.00-4.01 V
  • 22 uF capacitor + 10 ohm resistor -> 2.68 V

So my follow-up question here would be if this is expected output? And do I need to use one of the resistors if I want to connect the ESP now?

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  • \$\begingroup\$ Aren't you supposed to use the Vout pin (2) for the Vout? Or is the TAB connected to Vout? \$\endgroup\$
    – jonk
    Commented Apr 17, 2021 at 18:07
  • \$\begingroup\$ Are the capacitors populated at this point? Is there a load on the regulator? \$\endgroup\$ Commented Apr 17, 2021 at 18:08
  • \$\begingroup\$ A very warm welcome to the site. How do you know that the supply is 5.1..5.4 V Is that just what's written on it or have you measured it with a scope? What test equipment have you available? A DMM will give you an average value. \$\endgroup\$
    – TonyM
    Commented Apr 17, 2021 at 18:08
  • \$\begingroup\$ @jonk, no. I added a note on that to the question. \$\endgroup\$
    – TonyM
    Commented Apr 17, 2021 at 18:09
  • \$\begingroup\$ Ground should and clearly can-be a full plane on the blue-track side. \$\endgroup\$
    – Andy aka
    Commented Apr 17, 2021 at 18:16

4 Answers 4

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The datasheet recommends a 22uF tantalum capacitor on the output. (The tantalum will have a higher ESR than ceramic and the ESR zero likely helps stabilize the loop.) The 0.1uF ceramic cap you show on the output likely isn't enough.

The layout isn't great either, the caps could be closer to the regulator with thicker traces, or even copper pours for the voltage rails.

Have you checked the output on a scope? That would show if it's unstable and oscillating due to the lack of enough output capacitance.

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  • \$\begingroup\$ you mean replace C8 with a 22uF right? I will try that! I only have a multimeter which shows the 4.4V at the regulators output. Probably I can not measure stability and oscillation with that. \$\endgroup\$ Commented Apr 17, 2021 at 19:46
  • \$\begingroup\$ @JohannesKramer Set multimeter to AC. You will see oscillating. \$\endgroup\$
    – user263983
    Commented Apr 17, 2021 at 20:07
  • \$\begingroup\$ I didnt have any tantulum capacitors, so I ordered some with 22uF. I tried connecting a 10uF electrolytic capacitor to the output though...but I did not change anything - is that expected behaviour? \$\endgroup\$ Commented Apr 18, 2021 at 11:29
  • \$\begingroup\$ @JohannesKrämer No, I would expect a 10uF electrolytic to help. Two other things are not clear- Did you try a load on the output of the regulator? Just a resistor to ground would be fine. Also as Tony mentioned below your regulator can't sink current so be sure there are no devices driving current into the LDO's output. If those things are sorted and the 22uF cap doesn't help then you may have a damaged regulator. \$\endgroup\$
    – John D
    Commented Apr 18, 2021 at 17:14
  • \$\begingroup\$ @JohnD I tried that now, I updated my original post with the results I got. Do these results make sense to you? And...how do I know that no other device are driving current into the LDO's output? \$\endgroup\$ Commented Apr 22, 2021 at 18:55
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AMS1117 seems popular, probably because it sells for 2 cents on aliexpress. That's most likely counterfeit chips though, so you don't know what you're getting. Also, if a 2 cents regulator requires a special snowflake expensive capacitor, then it is no longer a 2 cents regulator.

If you like part numbers ending in 1117, I recommend LDL1117 from ST. It works with a 10µF ceramic cap, and it's also pretty cheap.

I am new in DIY and this is the first PCB I designed myself

OK, so advice:

The ESP draws quite a lot of current and I've seen a few people here that had trouble with AMS1117, it seems it is not that quick to respond to load current variation, so if you get problems like your micro randomly crashing, increase the capacitance on the output (any old electrolytic capacitor >100µF will do) and if that solves it, use a LDL1117 instead.

This SOT223 package dissipates heat through the tab, which should be connected to a copper area used as a heat sink. Since you did not, the LDO could get quite hot if the ESP uses wifi a lot. If it gets too hot and you do another board, you can either pick a regulator that has GND on the tab and connect that to the ground plane, or connect it to some copper tied to Vout on one side of the board.

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  • \$\begingroup\$ 1. I ordered here because the shop is connected to EasyEDA: lcsc.com/en (not sure if this is a good brand or not) 2. My main priority was not the price but rather to get the stuff work at all. So I basically ordered the components that were used by people (in videos or blogposts) in similar projects. But I will keep your recommendation about LDL1117 in mind, thank you! My main question at this point: is it save to connect the ESP now and try it out (or will I destroy it with the current setup)? If so, with or without the resistors mentioned in my updated post? \$\endgroup\$ Commented Apr 23, 2021 at 19:57
  • \$\begingroup\$ I will also do some more experiments with a >100uF capacitor. \$\endgroup\$ Commented Apr 23, 2021 at 19:58
  • \$\begingroup\$ If you are measuring 4V at the output of a 3V3 LDO then something is wrong and needs investigating, don't put the ESP until you know what is wrong. It could be the LDO oscillating a bit and the multimeter is getting the measurement wrong, or it could be something else. Did you check if your multimeter is working? \$\endgroup\$
    – bobflux
    Commented Apr 23, 2021 at 20:44
  • \$\begingroup\$ The 4V output is a bit outdated by now. This was the initial situation, but since then I have received a lot of feedback concerning load and capacitor. Please refer to the latest measurements in the UPDATE section of my original post. Multimeter should be working fine (I tested it on some other devices and the results are reasonable). \$\endgroup\$ Commented Apr 23, 2021 at 20:54
  • \$\begingroup\$ I ordered LDL1117 and soldered it onto the board. Unfortunately now something completely weird is happening: source is still 5V but after soldering the LDL1117 onto the board only 1.3V arrive at the board, and behind the LDO its only 0.7. After removing the LDO, the full 5V arrived at the board again. How come the LDO is affecting voltage even at the pins where the source is connected? \$\endgroup\$ Commented May 8, 2021 at 19:00
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You are perhaps not familiar with LDO’s are pullup only regulators and , pull down from the load.

Yet you have a LED load coming from 5V and driving low from 3.3V uC. since the LEDs pullup more than the uC pulls down as a lid on 3.3V the LDO voltage rises to an equilibrium where the output current is now zero.

Thus can be remedied with a a load resistor to ground on each driver pull the equilibrium down to 3.3V so the LDO is now supplying the minimum rated current, which the datasheet indicates as 5mA typ, 10mA max added to your LED load current.

I don’t see any current limiting resistors, except the uC CMOS drivers will be 25 Ohms +/-50%. if you define your LEDs, then R load can be computed.

If they are IR, Red or Yellow, don’t use 5V on the LED’s rather use 3.3. then you may avoid this issue. Normally RGB LEDs only need 2V min to 5V if using those. Show links.

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  • \$\begingroup\$ Is this also an issue as long as the LEDs are not connected to the board? As a first step I would like to get the voltage right and then connect the ESP to make the internal LED blink. Once that works I would go on and also connect the RGB LEDs to the board. \$\endgroup\$ Commented Apr 17, 2021 at 19:51
  • \$\begingroup\$ Read the LED interface specs \$\endgroup\$ Commented Apr 18, 2021 at 0:14
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There are most likely two factors affecting this.

First one is the output capacitor. Basically, there is much less output capacitance than suggested for stability under all conditions, and the capacitor is of wrong type. 100nF ceramic capacitors have extremely low ESR compared to the suggested tantalum capacitors. The fact that the output capacitor is further away from the regulator might even help a bit, as it is sometimes suggested when replacing tantalums with ceramics. However, 100nF can still be too low value.

Second thing is that there is no load at all. While the fixed 3.3V version should internally consume about 5mA which should make it stable, the datasheet does mention that the regulators will be stable under most conditions when it has a 10mA load.

Try to give the regulator a load, if nothing else, a 330 ohm resistor. If that does not help, add more output capacitance.

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  • \$\begingroup\$ I ordered 22uF tantulum capacitors and will try with them. But how can I put load on the regulator without connecting the ESP to the board? \$\endgroup\$ Commented Apr 18, 2021 at 11:26
  • \$\begingroup\$ I did mention in my answer that if you have no other load then put a 330 ohm resistor. Or a couple of LEDs with their series resistor. Or other lamps or motors or whatever you happen to have. \$\endgroup\$
    – Justme
    Commented Apr 18, 2021 at 11:45

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