ESP8266 Datasheet and Logic Levels questions

[DaveTheWhiteAsian]

Hey Everybody,

I’ve been searching the internet for a Datasheet for the ESP8266 but have been unsuccessful at this point. If anybody has this could you shoot it my way?

… we’re having trouble with the interface between the master and slave modules. Looking through the schematics and probing voltages, it appears that the slave module’s I/O expander operates on +5V, while the master module generates 3.3V logic signals. It looks like these 3v3-logic signals are at the cusp of being interpreted by the PCA9555 I/O expander on the slave module. Has anyone else found this?

[Ray]

ESP8266’s technical documents are all listed here:
https://www.espressif.com/en/products/socs/esp8266

PCA9555 is a I2C device, for I2C device, because the data lines are pulled high by the microcontroller, and the slave devices only pull these data lines to ground, it’s ok to have a 3.3V microcontroller interfacing with a PC9555 powered by 5V. 3.3V is within the high logic range of PCA9555, so this works fine.

[PeterTheRed]

Hi Ray, Thanks for the response. My name is Peter, and I’m working with Dave on this issue.

Looking at the datasheet for the PCA9555, I see that VIH, input HIGH voltage for SDA/SCL pins > 0.7 * Vdd. (see attached screen capture)

For Vdd = 5.0V, 0.7*Vdd = 3.5V, which is higher than the 3.3V logic signals generated by the MCU.

I’m working on adding a FET based level shifter to this ckt and some local pull-ups to 5V on the slave-side to see if that doesn’t resolve things.

Thanks,
Peter

Attachments:

1. 

   PCA9555_Spec.png
   

[Ray]

Yes, I am aware of the datasheet, but we’ve never had any problem using 3.3V ESP8266 to drive 5V PCA9555. If you believe it’s a problem you can simply add a diode in series between 5V and PCA9555’s VCC pin, so that will drop 0.7V and supply 4.3V to PCA9555. This way 3.3V/4.3V > 75%.

[Author]

Posts