DISCHARGE_3V3 Pin in Cygnet

Hardware Cygnet
1

Hi everyone,

I’m trying to better understand the purpose of the “DISCHARGE_3V3” connection in the Cygnet schematic.

In the diagram, the R11 resistor (1K) is connected between the 3V3 output of U2 and pin 6 (PH1-OSC OUT) of the microcontroller U1, and the net is labeled DISCHARGE_3V3.

Could someone explain the intended function of this resistor and signal?

Also, is it possible to change the behavior or configuration of this pin? In the Swan, the pin that performs a similar function is a Digital IO.

Thanks in advance for any clarification.

2

Hi @yordanyre,

The DISCHARGE_3V3 pin on the Cygnet lets the MCU help drain the 3.3V rail when that rail is being turned off, and the 1K resistor limits current so that discharge happens safely. This pin is intended specifically for controlled discharge of the 3.3V rail, not as a general-purpose Digital IO. We don’t recommend repurposing or changing its behavior unless it is being used for that discharge function.

But if you are, here is our recommended usage pattern:

void enable3V3Regulator() {
  digitalWrite(DISCHARGE_3V3, DISABLE_DISCHARGING);
  digitalWrite(ENABLE_3V3, HIGH);
}

void disable3V3Regulator() {
  digitalWrite(ENABLE_3V3, LOW);
  digitalWrite(DISCHARGE_3V3, ENABLE_DISCHARGING);
  delay(1);
  digitalWrite(DISCHARGE_3V3, DISABLE_DISCHARGING);
}

I hope that helps!

Rob

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