ESP32 Forum

I used STBB1-APUR in my project, which is a switch-mode buck-boost power supply IC with 1A (peak 2.3A @ 3.3V) output capability. I used it to stabilize the voltage from Li-ion battery to 3.3V, and the 3.3V output is directly connected to the ESP32 power supply pins. But my ESP32 suffers from power brownout when performing wifi scan, which considered consume more power since it uses RF functionality.

The input capacitor is configured as 10uF, the output is 22uF, and the power inductor is 2.2mH according to the datasheet suggestion. The schematic is shown below: Increasing the output capacitor gets rid of this problem (shunt a 220uF capacitor with the 22uF one), but it will also increase the volume of my PCB which is not good. Additionally, the brownout problem emerges again when the camera module(ov2640) is added, which claims the maximum current is 100mA. INFO:
ESP32 Module:
ESP32-PICO-D4
SMPS IC:
STBB1-APUR -- 1A (peak 2.3A @ 3.3V) output capability
Capacitors connected to ESP32 Vin:
22uF at STBB1-APUR output; 10uF and 100nF near ESP32

I wonder why ESP32 would brownout since the current is away below the limit of STBB-APUR, and the way that can solve the problem.
Please leave a comment below if you have any idea.
There are some solutions that I got from others:
1. Add an extra linear regulator with its required capacitors in the middle of SMPS and ESP32
2. Use the Remote Sense Mode connection. Sensing the voltage near ESP32 Vin pins.
3. Use more ideal capacitor types, like tantalum capacitors, but with a smaller value than the 220uF aluminium capacitor to reduce the size

What type of capacitor is the 22uF one, and can you describe the power lines between the PSU and the ESP32? (Traces, wires, ..., how thick, ...)? Just for reference, when does the ESP32 brown out exactly? Also, you say 'when the camera module is added', I hope you don't mean you're hotplugging that? Also, are you sure if it's the SMPS that's browning out, and not, say, the LiIon battery side?

Thank for your reply :]

The 22uF capacitor I used was a 0805/10V X7R SMD unpolarized capacitor.

The 3.3V wires are 20mil width and 1oz thick. (Okay, I just noticed a narrow wire near the capacitor of power pins. Will there be any significant influence?) In terms of the timing of brownout, I think it was exactly when the scanning starts when Wifi scan program was loaded since the brownout log is printed on the console just after the user-app start line. When working with the camera program, the brownout point seems also related to RF. The program worked during the camera initialization, but when it tried to start the HTTP server, it started to brownout. (the tested program is a video streaming program, which can be found at:https://github.com/igrr/esp32-cam-demo)

And, No, I didn't hotplug it. I connected it when the power is down.

Also, I think the problem should not come from the input side of SWPS since I am currently using USB to power the circuit. The battery is left unconnected. And it is done through a battery management circuit which is LTC4067.

An USB lead isn't always the best for high loads... can you try to see if moving the 220uF capacitor to the input side of the SMPS makes a difference?

Also LTC4067 has a current limiting function

WiFive wrote: ↑

Wed May 08, 2019 7:28 am

Also LTC4067 has a current limiting function

Yes, I know. But I set it to 2A, the maximum.

ESP_Sprite wrote: ↑

Wed May 08, 2019 6:03 am

An USB lead isn't always the best for high loads... can you try to see if moving the 220uF capacitor to the input side of the SMPS makes a difference?

Make sense. I will try it and update the problem later.

I would put a big polarised capacitor on the output 220uF or so to assist with surges