Power, LDO Regulators - mhightower83/Arduino-ESP8266-misc GitHub Wiki

TODO - revise view:

  • This has some useful information to integrate. https://www.eevblog.com/forum/projects/esp8266-power-supply-issues/
  • Espressif FAQ claims Analog 350ma Peak and Digital 200ma Peak required
    • Hmm, Digital 200ma may include current to drive output pins hard.
    • Elsewhere 500ma is the recommended PS value.
    • In the context of Analog 350ma and lightly driving digital pins, the ME6211 doesn't look as bad; however, the ESP8266 is operating in a range under-documented by the part's datasheet.

Some LDO Regulators commonly used with the ESP8266

WIP - still trying to get all the specifics right

Contents

Power Demands of the ESP8266

In the Espressif's Hardware Design Guideline, section 1.4.1.2. the notes specify "When using a single power supply, the recommended output current is 500mA." Not emphasized in their description is that the 500mA is for peak demand (transient load) not continuous. Also, the various ESP Modules that I have seen are all using a single power supply.

While the typical transmit power consumption of the ESP8266 is documented as 170mA/140mA/120mA for operating in 802.11b/g/n mode, I never found any other details in Espressif documents on how or when it would pull close to 500mA. It appears this transient load is at startup. I found this article at Ondrovo.com "Determining the ESP8266 power consumption", which shows around 430mA at startup. I am not sure his value had the aid of a low ESR CAPS around the ESP8266.

Looking at various designs I see a number of different LDO Regulators used with the ESP8266. Most of the variety I have seen has been on Development Boards. It seems that line-powered IoT devices mostly just use the LM1117 or its equal from various manufactures. Many of the LM1117 variants can handle 800mA continuously with proper heat dissipation support.

The area I will try to highlight on this page is the use of very small low-power dissipating LDO Regulators. These devices are smaller than a grain of dry rice (SOT-353 package) and are asked to handle 500mA. A quick calculation shows that it would need to dissipate 850mW if it were not a transient load. That is based on a supply input voltage of 5.0Volts and a regulated output of 3.3V with a current of 500mA. Fortunately, the 500mA load is not continuous. Their use in an ESP8266 design relies on the average power being substantially less than 500mA. That said, the part still needs to be rated for the full 500mA in order to maintain line regulation and a low ripple for stable ESP8266 operation.

Side note, there is often a series Schottky diode between the USB port +5 and the input to the LDO regulator. At 500mA the voltage drop can be in the area of 440mV (220mW). This blocking diode has the side effect of helping offset the total power dissipation required of the LDO regulator.

A common property of the non-LM1117s is low Quiescent Current consumption in the uA area vs the 5mA - 10mA for the LM1117. Which no doubt makes them more desirable for battery-powered devices.

Texas Instruments LP38692

Datasheet Texas Instruments LP38692 - CMOS LDO Regulator, 1A

Nice datasheet. It clearly shows Load Regulation and Voltage Dropout for the advertised operational current range up to 1A. It has a nice Low Dropout Voltage of 450mV at the 1A maximum operating current.

This looks like an excellent choice for use with the ESP8266. And, at 1A, there is a reserve capacity to support small peripherals; however, as impressive as 1A is for such a tiny component, the total power available will depend on the heat dissipation of the board design and the heat management components.

So far the only place I have seen this part used was in the schematics for a WiFi/IoT Display Module (ESP8266 based) made by 4D Systems.

Diodes International AP2112

Datasheet Diodes International AP2112 - CMOS LDO Regulator, 600mA

Nice datasheet. It clearly shows Load Regulation and Voltage Dropout for the advertised operational current range up to 600mA. Adafruit shows this on the Adafruit Feather HUZZAH ESP8266 schematic.

This looks like an excellent choice for use with the ESP8266. And, at 600mA, there is some reserve capacity for small peripherals; however, this will be limited by the heat dissipation of the board design.

Richtek RT9013

Datasheet Richtek RT9013, (backup link) - CMOS LDO Regulator, 500mA

This one looks nice. While it has an Absolute Maximum Ratings section, it does not specify a value for output current. However, the part addresses the issue by having Current Limit Protection and Thermal Shutdown Protection. The typical dropout voltage @ 500mA is specified in the feature list. And, it is detailed in the "Electrical Characteristics" section for the part voltage range it applies to. Also, given is the maximum dropout voltage of 400mV @500mA. This is good information. These are things we must know to make good design decisions.

This looks like a good choice for use with the ESP8266.

Torex Semiconductor XC6204 Marked 4A2X and 4B2X

Datasheet Torex Semiconductor XC6204/XC6205 - CMOS LDO Regulator, available in 150mA or 300mA parts

I have not seen this part on an ESP8266 Development Board Schematic; however, it shows up on a lot of the boards manufactured and sold. I see it often used as an inferior substitute for the LDO part specified on the schematics. And it is mostly the 150mA part that is being used. A longer datasheet discussion can be found here.

...

Looks like it is a good regulator for its current class; however, I don't see it as a good choice for the ESP8266.

MicrOne's ME6211

The manufacturer's site, http://www.microne.com.cn, is very slow when it is working and I could not find an English datasheet or a Chinese datasheet that wasn't a bitmap. (hard to do a copy-paste for translation) To find a datasheet in English do an Internet search on the part number. The datasheet's Absolute Maximum Ratings section has 600mA as the maximum current. The "Maximum Output Current: 500mA" is specified with a (Vin-Vout) voltage drop of 1V; however, all additional operational parameters are specified for 100mA and 200mA outputs only. This leads me to believe this part's operational maximum is 200mA. While the dropout voltage for 500mA is missing in the "Electrical Characteristics" section, on the edge of a graph in the back, it indicates the dropout voltage around 670mV. The graphs for "Input Voltage VS. Output Voltage" only focus on 100mA and below. I see little data supporting operations above 200mA. I would have to assume those numbers between 200mA and 500mA will not be good. There is no indication of what "Line Regulation" is above 200mA and we will see a 435mA load at startup with the ESP8266.

Sometimes what is not said is more important than what is said.

This part is listed on most of the WeMos schematics. Of the WeMos boards I have and the photos I have seen, none of them show this part being used; however, it appears it is used. This article, Wemos-the-Clone-Wars, has a table showing some of the SMD marks used.

I suppose it works, after all, it is rated at 500mA? We have no idea what the 3.3V output will look like at 500mA. From the datasheet details (or lack of) and knowing the demands the ESP8266 has for power at startup, this does not look like a suitable LDO. I would not feel good about using this part on an ESP8266 Development Board. I think this is especially true if you are adding peripherals to the 3.3V supply output of a DEV board. It may be that board builders work with the manufacture to get the production lots of the part that meet some minimum standard. Or we just get lucky and sometimes the devices we order accidentally work.

Datasheet Links

References / Self Study