A while ago I had some trouble with a TPS73633 (see Troubleshooting handsoldered TPS73633 SOT-23 LDO whose output is unexpectedly high) . I didn't get the 3.3v output voltage that I was expecting, whatever I tried. Since I wan't sure whether the error was in my board design or somewhere else, and I wanted to get to the bottom of it, I designed a new board specifically for testing the TPS73633.
My final goal would be to use the TPS73633 to power a ESP8266.
My testing board looks like this:
it follows the "typical application circuit" design in the datasheet (http://www.ti.com/lit/ds/symlink/tps73633-ep.pdf). The board design looks like this:
Unfortunately, I do not get 3.3v out of it when I hook it up to one of these batteries:
At first I thought the problem was that I bought these ldo's cheaply in China, so I bought another batch to see if it woukld make any difference, and then I aven bought some from farnell, so I would be sure I had the real deal, but whatever I tried, I never got a output voltage of 3.3v. What I did get was 2v, 4v and 0.2v:
I even bought a few TPS73733DCQ ldo's, wich are basically the same thing in a SOT-223-6 package, but even those gave me 0.2v as output. So after all this testing I'm a bit lost at why I don't get a simple LDO to do what it should do.
I did all my tests while a load was attached ans with fully charged batteries. I also measured all connections and it doesn't seem like the problem is in my soldering skills.
The only other thing I could think of is that I either soldered at a too high temperature (300 c) or that there's something wrong with these batteries.
Does anyone have a clue what I'm doing wrong here?
As suggested by peufeu I removed all capacitors. That actually did the trick for most of the ldo's, i finally got 3.3v out of it (except for the Chinese ones from the first batch, I expect them to be counterfeits, they just give a output voltage that is the same as the input voltage).
After that discovery, I started adding capacitors again, since the datasheet suggest doing so, in this diagram:
In my original design I was using capacitors of 1uf, 0.22uf and 0.01uf. To be honest, I don't remember why I chose those values.
In the datasheet I only found this information:
Although an input capacitor is not required for stability, it is good analog design practice to connect a 0.1-µF to 1-µF low ESR capacitor across the input
it doesn't say anything about the value of the other 2 optional capacitors. I tried using a 1uf capacitor for all three capacitors, and that seems to work fine. Is there some standard rule as to what values you would use in a case like this?