Input-only pin GPIO36 sources current (backpower)

RMandR
Posts: 47
Joined: Mon Oct 29, 2018 3:13 pm

Input-only pin GPIO36 sources current (backpower)

Postby RMandR » Fri May 07, 2021 7:59 pm

I have GPIO36 attached to an LED and a 1K resistor to GND. GPIO36 is configured as input.

The LED is supposed to be switched on by another circuit. But the diode light up and stays on. It goes off if I hold down reset and also off if I add a diode to prevent reverse current. So it's definitely the pin that is powering the LED.

Shouldn't the input pin be high-impedance? If GPIO36 is input only and does not have pullup/down resistors, what's powering the LED?

The datasheet says it's also SENSOR_VP, could that be thing that powers the LED?

thx

ESP_Sprite
Posts: 4802
Joined: Thu Nov 26, 2015 4:08 am

Re: Input-only pin GPIO36 sources current (backpower)

Postby ESP_Sprite » Mon May 10, 2021 3:26 am

What's the voltage that's supposed to be on there? If it's >3.3V (or <0V) the ESD protection stuff in the ESP32 could potentially kick in and source current.

RMandR
Posts: 47
Joined: Mon Oct 29, 2018 3:13 pm

Re: Input-only pin GPIO36 sources current (backpower)

Postby RMandR » Wed May 12, 2021 1:42 pm

What's the voltage that's supposed to be on there? If it's >3.3V (or <0V) the ESD protection stuff in the ESP32 could potentially kick in and source current.
[Thanks ESP_Sprite]

If the current is flowing _out_ of the input pin, then esp32 VCC voltage would by definition be higher than the LED voltage and not >3.3V, correct?

That side of the circuit tied to PIN36 voltages are zero. However, from reading your comment, would it be possible:

VCC is ~3.12VDC and esp32 is connect to ESP_PROG with the power jumper of ESP_PROG removed. If the TX/RX pins connected to ESP_PROG are at 3.3V, would it then be possible for current to flow from the TX/RX pins connecting to ESP_PROG (3.3V) out through GPIO PIN 36? or any other pin for that matter?

-a

RMandR
Posts: 47
Joined: Mon Oct 29, 2018 3:13 pm

Re: Input-only pin GPIO36 sources current (backpower)

Postby RMandR » Wed May 12, 2021 1:44 pm

Edit: VCC is approx 3.12VDC. Typing a tilde (~) seems to get mapped to a minus (-) after it's posted.

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