I've been operating a DIY LiFePO4 BMS for a number of years. Recently I've made a change to the Sketch and now the two SPI peripherals (SD memory and LTC2452 (ADC)) fail to work. They work with ver. 2.0.11, not with 3.1.0. Ver. 3.1.0 will work with SD or the ADC separately but not together.

#define ...

With the 47 uF cap the module comes faster out of reset: 258 ms vs. 550 ms.

If you look at the top purple trace, you can see multiple shallow dips in the signal. I think the processor is trying to get started but can't as 3.3V isn't stable yet. It takes 550 ms before it decides to get going; even ...

The difference when adding 47 uf between pin EN to ground is significant.

Scope plots:
yellow = 6V power into 5V input
purple = IO pin 14


void setup() {
pinMode(14, OUTPUT);
delay(10);
digitalWrite(14, HIGH);
}


No added capacitance to EN:
During power-up IO 14 begins to ramp up to 3.3V ...

Some modules fail to power up. Power source is a12V battery. A Mini MP1584EN DC-DC Buck Converter drops voltage to 6V. The 6V powers the ESP32 module. It takes about 70 ms for the output of the DC/DC converter to ramp to 6V (yellow trace). The ESP 3.3V ramps up in 40 ms (purple trace).

P1004336 ...