Outline

• ESP8266 power demands
  • Interesting post at https://www.ondrovo.com/a/20170205-esp-self-destruct/
    • TODO: reread ResetInfo->reason is 6 (REASON_EXT_SYS_RST) even on power up. I've seen this with WeMos Pro. Add this here because of the power-related issue.
    • Walkaways,
      • too large a CAP on the 3.3V rail can slow the rise time at power-up causing catastrophic failure in the ESP8266.
      • I believe the ESP8266 datasheet has required rise time specifications for PD/RST/Power.
      • I think a lot of the voltage droop he shows will go away with proper board layout and the ESP8266 being closely nestled with a nice 3.3V LDO regulator.
  • His next post, https://www.ondrovo.com/a/20170207-esp-consumption/, provides useful readings for determining LDO Regulator parameters needed.
    • again the deep voltage droops should go away with a proper PCB and LDO regulator.
    • Need to put one of the dev boards on an oscilloscope and measure this.
• LDO Regulator operating parameters
  • Small size vs power dissipation
  • PCB is part of the heat management system.
    • This appears to be true for a lot of the SMD parts today.
  • High input voltage excess heat - failure
  • Looks like there are lots of knock-offs.
    • reference Reddit article on knockoff 4A2D parts
  • Too many 4A2D (150ma) parts in the wild and they should be 4A2D (300ma)
    • It is easy to miss the A vs A in the datasheet's table for the current specification.
    • It seems possible that 150ma may be okay when you consider average power consumption.
      • When you consider the time spent transmitting and consuming ~200ma compared to the rest of the time at 60-70ma.
      • For this to work the silicon must be the same as that which supports 300/500ma so that the peak consumption can be handled. Then, the resulting average power around a surge would need to be appropriate for the SOC-23 package.
        • I don't think the datasheet parameters cover this use case.
        • Because of power dissipation issues the input voltage cannot be too high.
        • And it cannot go too low else lose the ability to maintain a constant output at full load.
        • It may be a good idea to avoid using the Dev Board's 3.3V supply for anything off-board you want to connect.
    • The D indicates the lot number
    • For this part 4A2x most of the parts we see pictures of on the internet are from lot D
  • Some schematics will indicate 500ma parts for the LDO 3.3V regulator. When you look at the part on the board, you discover that a similar, but 300ma part, has been substituted.
  • Fast response to Transient Load changes.
    • 60ma to ~300ma
• Cell phone chargers used as 5V power supplies
  • Designed for steady current flow for charging batteries
    • Voltage regulation is less than optimal.
    • Output voltage levels vary
  • Poor Transient Load response
  • Inexpensive and many to chose from
    • Some really cheap adapters are fire and safety hazards
      • No isolation from Mains
      • poor construction
      • No Safety Agency approvals, eg. UL, ETL, CE, etc.
        • Why consider Safety Agency Approvals as a concern?
          • Component selection in critical areas will be limited to parts with well-defined failure modes. For example, ceramic capacitors can fail open or fail short. For a CAP that connects across the main for RF interference shunting, a fail short could cause a fire. You want a ceramic CAP that fails open - never short. These exist and are a verification check box for Safety approvals.
  • A Switch mode PS takes a few cycles to catch up to a transient load change resulting in voltage droop.
    • This leaves the +5V rail unsuitable for most other devices except relays and LEDs.
    • Some IoT devices try to use the +5V rail for power monitoring Chips. From what I have seen, they tend to have occasional erratic readings.
  • Capacitor on the +5V to help with transient load
    • Not much success
    • IoT devices tend to have a 500-680uF cap on the +5V rail. Dev boards tend to have 1uF to 10uF.
      • Dev Boards might perform better on 5V chargers with an additional 500uF CAP.
      • Also, verify the Dev Board already has a .1 to 1uf ceramic CAP.
• Computer Powered USB port
  • TI Application note Power Management - Powering electronics from the USB port
    • Maximum input capacitance 10uF
    • Maximum inrush 50uC
  • Should have a good Transient Load response
    • 60ma - 300ma would be a much smaller percentage of the overall load the PC Power supply would be dealing with.
• Powered USB Hub.
  • Transient Load response - Unknown, it might depend on the total load already being handled. The more the better.
• USB cablesFor
  • We use them for development to flash the module
  • We use them to provide power later.
  • The gauge of the wire and length may have an impact on our project's stability.
• USB connector quality issues, resistive connector
  • power loss represented by voltage drop
  • power loss => excess heat
  • failure
  • meltdown
  • fire
  • Amazon reviews of melted connectors and destroyed phone jacks.
  • poor wire to plug connection cold solder, bad crimp, failed crimp from stress, etc.