ESP8266 Community Forum

- Thu Jun 25, 2015 12:16 pm #21636

Lotus,
Can you help clarify the phrase "causing it to burn up". After using the 10k resistors and the chip got hot, do you mean that it is ruined or if one then drops to using 5k resistors it starts to work?

Neil

the 10k pull up on CH_PD would randomly cause the esp8266 to reset and into an unknown state where I would max out the 500mA supply source I am using. All this power was dropped on chip as the IC would get burning hot. This happened a few times to me for a few seconds and I would shut the supply down. The IC survived these occurrences.

Obviously, if I left the supply on longer or had a heftier source I would probably have destroyed the chip.

- Sat Jun 27, 2015 5:39 pm #21881

Ok here is the next (and hopefully final) version. I added a capacitor to the reset line (is that done right?) and a voltage divider on the adc pin which should break down 3.3V signals to a 01-V range.
Last question remaining for me at the moment: what is the best practice with unused pins in a pcb with the esp? Say I don't need to use the adc and GPIO 14. I guess just leaving them floating isn't the best idea. But what is? Connecting them to ground? With a pulldown?

Thanks again for the help (espacially Georgeloak)!
I hope this might someday help other newbies with esp board development

Use 5 kohm for pullups, 10kohm is too weak. 10 kohm works ok for the pulldowns. Also a 100 pF cap to ground on the EXT_RSTB pin helps with noise false triggers.

From my experimentation I am able to consistently put the IC in an unknown state causing it to burn up with a 10 kohm pull up on the CHIP_EN pin.

You can refer to the appendix in Espressif's latest hardware users guide.

Just to be sure, what pin do you mean with EXT_RSTB? The reset one in my schematics and/or the connected 16, or another one?
Do you have a link to this hardware guide? I can't find a guide which explains what you just wrote

- Sun Jun 28, 2015 9:26 am #21903 EXT_RSTB is the pin name assigned to the actual ESP8266 chip and is connected to the rest in your schematic. You have 470pF which is good, no need to reduce to 100pF. The latest hardware manual does show 5k pull ups which is rather "strong" compared to industry standards but apparently this has helped solve some issues for other people. I'm not 100% convinced this is the root of the problem but it doesn't hurt to use 5k values.

The combination of this pull up and the capacitor creates what is called a RC constant and the combination of these 2 parts determines how long the signal at reset will stay low. t = R * C so increasing either value holds the signal lower for a longer time. This is a good thing as it allows all of the other circuits to stabilize before you bring the ESP8266 out of reset. You can find many examples of the RC circuit on the internet and can see the change of the signal when changing the resistor or capacitor values.

The hardware manual can be downloaded from http://bbs.espressif.com/download/file.php?id=486

- Mon Jun 29, 2015 1:11 pm #21993 It took over 2 months (and one lost shipment) but I finally got some ESP12's to play with, so this information is appreciated. Thanks LastSamurai for the reference drawing, and thanks to all who contributed to it