Supply Voltage Dropping to 1.5V on Start. Somehow related to EN pin

[ManuelODIS]

Hello,

i have a really strange problem with our custom ESP32-Wroom board.

We are using a ISL9122AIINZ-T DCDC converter to generate the 3.3V from our battery. (I2C of the ISL is pulled up to VCC as in the datasheet)

The DCDC converter alone works fine ( we have 2 separate boards, the ESP is on the second one) i tried to put some load on it and it went on working fine up to 100mA.

But as soon as I Attach the ESP-Board, the voltage from the DCDC converter drops down to 1.5V. There is no short circuit as my power supply does not show any current ( >1mA) flowing. As soon as i detach the ESP-Board the supply goes back to 3.3V

Now the really strange part: when i pull the EN-Pin of the ESP down for just a moment (touch the pin with a cable connected to mass) the power supply jumps on the right 3.3V.
Once there the board work as intended.

If I switch on and off the power supply, or disconnect and reconnect the LCM board, the DCDC converter goes back to 1.5V.

We "solved" the problem by changing the RC-Circuit on the EN pin from10k/100nF to 100k/1uF which makes it start 100 times slower then given in the ESP-Reference.

I really have no clue, how the EN-Pin can impact the supply voltage whiteout generating some sort of short circuit.

I already excluded every other possibility on out boards by removing all components except the DCDC converter and the ESP32 from our boards.

Any help is appreciated

Edit:

clarity

[ESP_Sprite]

Depending on the capacitors in your circuit, it could be that when you attach the board, the combined inrush current of the caps plus the startup current of the ESP32 overloads your converter. By staggering the cap inrush current and the ESP32 turning on, the converter can seemingly sustain the current just fine. Note that 10K/100n is on the low side; I'm decently sure our datasheets advise at least 10K/1uF.