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Simplest reset sequencing circuitry

Posted: Tue Sep 24, 2019 5:03 am
by cnlohr
Several designs (and admittedly my own) use the ESP8266/ESP8285 with only minimal reset circuitry, and sometimes hard-wiring CHIP_EN to VDD instead of following the sequencing outlined in the Espressif FAQ 1.4 and ESP8285 datasheet . Sometimes we use espressif parts where such sequencing is very difficult to fit/arrange. Can espressif comment on the minimal possible configuration for safely booting ESP8266's and ESP8285's? I.e. resistor between VCC and EXT_RSTB, capacitor on CHIP_EN, etc, since all I can find is just configurations that people out in the wild have preferred, as well as a specific instance on your WROOM where a 10k+0.1uF RC is used on CHIP_EN. We can also make some assumptions about the power-on time, i.e. <200 us.

This question is specific to situations where no deep-sleep is required.

Some specific questions arise out of this:

(1) What are minimum recommended resistor/capacitor combinations for EXT_RSTB and CHIP_EN?
(2) Can we tie EXT_RSTB to VDD if we properly sequence CHIP_EN?
(3) What is the internal pull-up/pull-down configuration of CHIP_EN?
(4) Is the reset circuitry and suggestions for ESP8266 and ESP8285 identical?
(5) Though non-ideal for high noise environments, can the EXT_RSTB pin be left floating if no trace is attached?
(6) If we connect CHIP_EN to GPIO16, is any other connection required?