EN pulse output at 10Hz

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Joined: Tue Feb 02, 2016 6:47 pm

EN pulse output at 10Hz

Postby mikeatom » Thu May 05, 2016 11:59 pm


The attached screenshot shows a pulse that seems to be generated from the ESP-WROOM-02 "EN" pin. The pulse width is 1ms, and it repeats every 100ms. In the region of 300-400mV.

Is there any chance the ESP module is causing this pulse?
I have isolated the power supply (3.3V), and also tried battery power (approx. 3.1V). It seems too regular to be instability?

Maybe someone else has come across something similar... (Hope :). Any ideas out there what could cause this?

EN is pulled up by 10K, and then is led out to a hdr via a schottky diode, so that user can apply GND to reset the module.

Thank you.

Posts: 140
Joined: Mon Oct 27, 2014 10:40 am

Re: EN pulse output at 10Hz

Postby Espressif_Kelly » Fri May 06, 2016 2:37 pm


Please help confirm if it is due to the variation of power supply. Because ESP8266EX will send beacon every 100ms in softAP mode.

More questions, please let us know.


Posts: 10
Joined: Tue Feb 02, 2016 6:47 pm

Re: EN pulse output at 10Hz

Postby mikeatom » Fri May 06, 2016 4:13 pm

Thank you for the help- That sounds like it.

What is the expected current requirement for ESP module when transmitting the beacon?

If you have a figure for current and duration, then I could calculate a suitable capacitor to handle the ripple.

Let me see... I have these data from the datasheet:

Voltage supply: 3.3V
Minimum supply: 3.0V
Peak current: 170mA

So the maximum voltage droop allowed is 300mV, and assuming the peak current is 170mA for the beacon tx. Then I just need the beacon duration. From the scope image, that would seem to be 1ms. Would you agree with these figures, or could you recommend other values.

Posts: 10
Joined: Tue Feb 02, 2016 6:47 pm

Re: EN pulse output at 10Hz

Postby mikeatom » Fri May 06, 2016 5:42 pm

Using standard formula:

Code: Select all

C = Q / U = (I x Δt) / ΔU

C = capacitance (Farad)
Δt = discharge time (here: 1000μs)
Q = charge
ΔU = voltage change (here: max. 100mV)
I = current (here: 0.3A)

This assumes the capacitor should handle a pulse up to 300mA for 1ms, whilst not allowing V to droop more than 100mV.

So the result is:
C = 0.3A x 1000μs / 100mV = 3μF


However, I understood the ESP-WROOM-02 module had an internal 10uF bulk cap. So an external 3uF cap should not be necessary?

Perhaps my math is wrong, or else maybe the ESP module is peaking for some short duration at much higher than 300mA during TX? Or perhaps the pulse width is wider than 1ms?

(I could also be unlucky and have a high impedance trace picking up the beacon signal, but I'd like to rule out the transmit-peak-current theory first).

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