Trouble with the Enable pin on a Voltage Regulator

Firmware
1

I'm using the MCP1640T-I/CHY in the following setup:

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MCP_EN is connected to C2 on my Electron. The R1/R2 configuration ensures Vout is 5V.

The datasheet mentions the following about the Enable pin:

So by pulling C2 low, I want to disable the regulator.This is crucial, as I have components with a very high quiescent current connected to Vout, and I need my setup to draw as little current as possible in Deep Sleep. I use the following code for this:

SYSTEM_MODE(SEMI_AUTOMATIC);
const int MCP_EN = C2;

void setup(){
    Serial.begin(9600);
    pinMode(MCP_EN, OUTPUT);
}

void loop() {
    digitalWrite(MCP_EN, HIGH);
    delay(5000);
    digitalWrite(MCP_EN, LOW);
    delay(5000);
    System.sleep(SLEEP_MODE_DEEP, 10000);
}

Observations: While EN is high, Vout is 5V. When EN is pulled low, Vout starts dropping towards 0V. When the Electron enters Deep Sleep, Vout goes back to 5V after about a second. EN appears to remain at 0V. The components connected to Vout continue to draw a lot of current while the Electron is in Deep Sleep.

What am I misunderstanding about the functionality of this device? It'd be great if someone could give me a push in the right direction here...

2

In SLEEP_MODE_DEEP all pins are put in high impedance mode.

You probably need to add a pull-down on the EN pin to prevent it from floating and causing the regulator to enable.

2 Likes
3

Noob question: is it possible to maintain this LOW state throughout Deep Sleep without adding an additional resistor to my setup? (i.e. just relying on the Electron’s features)

4

@Vitesze, not in Deep Sleep but it can be done in STOP sleep modes since the pin states are preserved but power consumption is not as low.

2 Likes
5

Thanks. Unfortunately, the 2.75mA draw in Stop Sleep is quite a lot (17x) higher than Deep Sleep so this will really hurt the lifespan of my setup. I’ll probably just add a pulldown resistor to it.

7

Just one more question: what would the most ideal value for a pulldown resistor be here? Would something similar to the internal pull-up be preferable (~40K if I’m not mistaken)?

8

@Vitesze, 10K will do. 47K might work also.

1 Like