What linear voltage regulator alternatives are there for use in IOT applications?
&quot;What LDO for IoT&quot; is too vague because &quot;Internet of Things&quot; is just huge. However, considering your choice of ESP32, we can narrow that down. So what parameters of this LDO are important and what parameters are not?
First requirement of any regulator is not to overheat:

At max load and dropout voltage, it should handle the dissipation. P=IV, DeltaT = PRth, compute max dissipation power, find thermal solution ie ground plane heat sink, compute max allowable RthJC, decide appropriate package, for instance SOT89 or SOT223 or something similar that has proper thermal path, ie not SOT23.

Sub-requirement: when the thermal tab of your IC is GND things are simple because you have a ground plane already. If the tab is Vout, and you don't have a power plane, you have a problem. Sure AMS1117 is tiny but the tab is Vout, so it's like this chip feels so special it just requires you to dedicate a huge copper pour on your board for no other reason than to cool it, and that tiny SMD now takes as much space as a TO220. And now you'll try to shrink the copper pour because it takes too much space, and you'll have to spend time doing thermal calculations to know if it will fry, all this to save 2 cents. When the tab is GND, the whole ground plane is the heat sink.


Load is a micro, not sensitive analog electronics, therefore:

Output noise: not important
PSRR: meh, not important, it'll be powered from a regulated 5V or batteries anyway

But, it's a big dual core 240Mhz micro with a WiFi radio that draws substantial current spikes. It also has various sleep modes which means it can go from drawing microamps to 200mA in a really short time. So I'll interpret &quot;LDO for IoT&quot; as a LDO that can handle a load that sleeps then bursts.

Transient response: important, especially steps between very low currents and nominal

Also an important parameter for implementation is output capacitor type. Some LDOs require capacitors with some amount of ESR for stability, and some are fine with a ceramic cap which has a tiny ESR of a few mOhms. Since ESP32 is sleek and thin, it would be good taste to associate it with ceramic caps.
So, for example, a LDO that costs 5 cents but feels special enough to require a 50c capacitor with &quot;special ESR&quot; ends up costing more than a 30 cents LDO that is happy with a 1 cent capacitor. And if the device is used outside in winter, the ESR of your non-ceramic caps will vary a lot... Will it always be stable?
ESP32 module has ceramic caps on its tiny PCB so the HF decoupling part is already done. So there is absolutely no technical reason that says it's not okay to stick a 1000µF electrolytic capacitor; but cost and aesthetics matter and MLCCs are cheap and tiny. Since ESP32 is a bit of a power hog, let's say 10µF. So:

Output capacitor requirements: stable with 10µF X7R MLCC

If you were using a battery and not a 5V power supply, you might add conditions about:

Quiescent current

Dropout voltage (here we have 1.7V margin, so any LDO will do that)

Transient response when dropout voltage is low


So, now you have all the required selection criteria to weed out the parts you don't want. Enter the info into the mouser/digikey search engine and... you'll probably have tons of results.
Sort by price, click on datasheets.
You're using ceramic caps on the output. So, Ctrl-F, &quot;capa&quot;, ENTER. If it highlights &quot;stable with ceramic caps&quot;, good. Otherwise, next. If it specs a minimum ESR value like 0.1 ohm or something, or i it says &quot;requires tantalum&quot; or &quot;aluminium cap&quot; on the output (which is another way to say &quot;high ESR&quot;) then next.
For example this is the case with AMS1117. It says &quot;22µF solid tantalum&quot;. Why put an expensive tantalum cap after a super cheap regulator? That's because it's an old chip design from the days when big ceramic caps were expensive. Now ceramics are cheap, so the new LDOs are pretty much all designed for ceramics. Cross-check with LM1117 datasheet:

So... next. Unless you put an aluminium cap, in this case it will work. With just ceramics it'll be unstable.
Note this is a different problem than HT7333. HT7333 is micropower, micropower regulators tend to be slow, and this one is extremely slow. It's probably designed for low power stuff that draws more or less constant current. AMS1117 is not slow, in fact it's pretty good, but its topology makes it unstable with low ESR caps, so it'll oscillate with ceramic caps. Result is the same, your micro will crash.
On AP2112 datasheet, hit Ctrl-F &quot;capa&quot; it says &quot;Stable with 1.0µF Flexible Cap: Ceramic, Tantalum and Aluminum Electrolytic&quot; like most modern LDOs.
So then you can check the rest of the specs.
How to read a transient response graph:
These vary a lot by manufacturer. Sometimes most of the information you need is obtained by noticing what is NOT shown on the graph.
The important thing is: during a load step will the voltage go out of the acceptable voltage range for the load?
Transconductance of PMOS used as pass device in LDOs increases with current, so at very low Iout you'll get higher output impedance and slower response. As current increases, transonductance increases, so things get snappier. If the graph shows &quot;0 to max load step&quot; then it's the worst case. If it shows &quot;10mA to max load step&quot; then they're not showing the worst case.
Likewise PMOS perform better with higher Vds. At low droupout voltage, when the PMOS begins to behave like a resistor, it needs a lot more gate drive so performance degrades. LDO behavior will be much worse at a dropout close to the lower limit than at say, 1 or 2 Volts. If the transient graphs say &quot;Vin=Vout+2V&quot; then it's not the worst case, and if you use it at a dropout of 0.5V it will be worse. If they show it for a dropout of say 0.5V then that's closer to a real use case.