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Power, USB Adapters
Most USB adapters are meant for charging devices and providing supplemental power to a battery-powered device. They are not designed to be the sole source of power. When a battery is charging, it is a relatively steady load. A sharp change in load is often referred to as a transient load. The chips commonly used for USB Adapter have a poor transient response since that was not a design goal. However, they are plentiful and inexpensive which makes them very attractive for use in cost-sensitive projects.
The ESP8266 during the boot process presents a big transient load. It goes from 80mA to 430mA. (Appears to be at transmit.) This can be an extreme challenge for an economy switch-mode power supply. (I suspect it's a challenge for most, if not all, SMPS.) The solution I see used for the ESP8266 is a good (most of the time) LDO Power Supply chip. Coupled with low ESR low ESL Ceramic or Tantalum capacitors on the output side. I have seen one ESP8266 development board that uses a low ESR low ESL 100uF Tantalum capacitor to help handle this surge.
All the line-powered IoT devices I have taken apart use an economy SMPS paired with the LDO Regulator approach. A downside to this is the 5.0V rail will sag at times. (Assume WiFi transmit)
This can be a problem if the design has 5.0V ICs that might be sensitive to power fluctuation. An example would be a power monitoring chip that has an analog element that needs clean power. In this case, a split 5.0V supply needs to be created. Depending on the severity of the sag, even other 5.0V digital parts may suffer if they share the ESP8266 LDO's 5.0V rail.
- How does a USB charger work? - A tear-down article on what is inside a USB Adapter.
Ref: Powering electronics from the USB port
- Of concern is the inrush current due to large capacitors on the +5 volt side. Suggested MAX input side capacitor of 10uf from Page 1, Table 1 of the reference.
TBA
- Keeping the Lights On - how to manage GPIO state across reboots and crashes
- Boot fails when SPI Bus used
- GPIO Drive Strength and Ringing
- LDO Regulators WIP
- ESP8266 Power Considerations This is only a rough outline, needs a lot of development.
- Upgrading Flash Chips, QIO, and DIO
- Dodgy Extra 2K of DRAM or CONT - WIP
- WDTracks - Print last call before WDT
- 5V Tolerant I/O?
Arduino IDE specific
Misc.
- Exception Causes
- ESP8266 will not boot
- Stacks sys and cont
- WIP Boot ROM and SDK Notes
- Multi-segment Boot ROM Loader, notes
- Cache_Read_Enable How to turn off and on instruction cache execution.