EN pin and RC circuit question

[chriselef]

Hello,

We have been working with an ESP-WROOM-32 module for about a month with great success on firmware development.

The module is on a PCB with just some basic supporting components (bypass caps, 3 buttons and 3 leds etc).
It works perfectly in regards to JTAG debugging, serial flashing and our custom firmware development.
The RC circuit we have is the default as it it is designed in the datasheet, a 10k resistor to 3.3V, a 100nF capacitor to ground and
a button that just shorts the capacitor.

The problem we encounter is that when we power off the module and after some time we power on, the module does not start.
It might start (maybe once per 20-30 times) if we press the "reset" button that shorts the capacitor connected to the EN pin.

If we remove the 100nF capacitor and replace the resistor with 1K then the module starts OK when powering off and on - no matter how many times we power off and on.


The module reports that it is a :
"ESP32 chip with 2 CPU cores, WiFi/BT/BLE, silicon revision 1, 4MB external"

Any help will be greatly appreciated...

Thanks,
Chris

PS: Don't know if posting the sdkconfig for the project might help

[hassan789]

Chip enable needs to be low for 150uS at each reset. Does your circuit gaurentee this? If not, better to use a voltage monitor. See latest datasheet for more detail.

[ESP_Angus]

Hi Chris,

What's the power source for the 3.3V line? Is it possible that it ramps up very slowly, or is unstable?

[chriselef]

Hi Chris,

What's the power source for the 3.3V line? Is it possible that it ramps up very slowly, or is unstable?

hello,

Thanks of the answer...
The power is coming from a bench top power supply...
Now, I am testing another ESP32 module and the behaviour is the same... it doesnt start

[ESP_Angus]

The power is coming from a bench top power supply...
Now, I am testing another ESP32 module and the behaviour is the same... it doesnt start

What else do you have at the module end? ie is there sufficient capacitance on the power pins near the module? Is the 3.3V coming directly from the bench supply into the module, or is there an LDO on the board? Are you able to post a photo of your setup?

The reason I'm asking these questions is that the only time I've seen these symptoms (failure to start from power on), the root cause has been initial power stability - ie the power ramps up too slowly or is unstable in some way.

[chriselef]

The power is coming from a bench top power supply...
Now, I am testing another ESP32 module and the behaviour is the same... it doesnt start

What else do you have at the module end? ie is there sufficient capacitance on the power pins near the module? Is the 3.3V coming directly from the bench supply into the module, or is there an LDO on the board? Are you able to post a photo of your setup?

The reason I'm asking these questions is that the only time I've seen these symptoms (failure to start from power on), the root cause has been initial power stability - ie the power ramps up too slowly or is unstable in some way.

Hello,

and thank you for your time..

I think that I have located the problem... On the prototype board, we had also a button that shorted IO0 pin
to ground, in parallel with that button there was a capacitor 100nF. So, when the power was applied this capacitor
until it was charged was holding the IO0 to ground with all the consequences...

By removing this 100nF capacitor it seems that all is ok..
I will keep testing this of course, but for the time being I will mark this thread a SOLVED

Yes we have a 10uF and a 100nF very close to the power pins of the module.

Thanks once again ESP_Angus!!