SparkFun Buck Regulator Breakout - 3.3V (AP63203) Only - Enable pin resistors question

Components & Accessories Power
1

Hi,

I have bought a bunch of these https://www.sparkfun.com/products/18356 which are great little boards. My question though is about the two 100k resistors R1 & R2 that are connected to EN on the AP63203.

Schematic: https://cdn.sparkfun.com/assets/0/7/c/f … ematic.pdf

Vin on my setup is 9V, and I’m using a 3.3v MCU GPIO pin attached to EN on the regulator, to enable/disable it. Without my MCU attached, EN would be sitting at about 4.5v. I’m concerned that that is higher tan the 3.3v max I should ever apply to the MCU GPIO pin. Normally the pin is configured as OUTPUT but before it is configured or if it was misconfigured as an INPUT, this would damage the MCU wouldn’t it?

What am I missing?

Thanks,

Paul

2

Having R1/R2 connected to EN also means the regulator will turn on all by itself when the circuit is powered up and it only gets shutdown when my MCU has booted and eventually pulls EN LOW. I kinda feel it would be better to either have EN not connected to anything other than the breakout pin OR have some jumpers we can cut if we don’t want to use it the way it comes by default. I’m thinking I will just remove R1 and R2 off mine and wire EN with an external pulldown so that the reg stays off until I explicitly tell it to come on with a 3.3v HIGH from my MCU GPIO to EN.

What do you think?

Thanks again,

Paul

3

Having removed R1 and R2 and using my own pulldown (I could have kept R2 I guess) I now have this great little reg behaving how I’d like. It’s off until I explicitly turn it on via a GPIO connected to EN. If I ever want it to come on automatically with Vin, I will just connect EN directly and only to Vin.

4

It seems like connecting EN and VIN directly is not a great idea.

I have bought an AP63203 BabyBuck Regulator Breakout - 3.3V and tried that. It fried the buck-converter.

Note, that this is the more compact version of this regulator. It has one less GND pin connector and no screw terminals: https://www.sparkfun.com/products/18357

Backstory:

I hoped to regulate an Input Voltage (VIN) of 12V-15V DC (from a car battery) down to a static 3,3V DC for running a small digital car clock with inside/outside thermometer.

Originally, the clock ran on 2x1,5V-LR44-batteries to provide 3V with low current draw, while the car was off. However, this battery-solution does not hold up very long, as soon as it’s cold outside. When it’s freezing cold in the winter, the 2 LR44-batteries were good for just 3 weeks of clock-runtime. And after that, they were flat and the clock always did reset to the default time.

So my thought was to connect the SparkFun BabyBuck Regulator Breakout - 3.3V (AP63203) to the car clock and supply it with 12V from the car battery to avoid frequent battery-exchanges in the future.

After getting the AP63203 3,3V BabyBuck Regulator, I read the instructions/shematic.

It describes:

“The EN pin is a high voltage pin and can be directly connected to VIN to automatically start up the device as VIN increases.” (see also the documentation of the AP63203WU-7 (6-Pin TSOT-26 chip) , top of page 11, link: https://cdn.sparkfun.com/assets/e/3/d/9 … P63205.pdf)

So thinking, I just need to pull EN high to enable the Regulator, I bridged VIN@12V directly to EN. The connection looked roughly like this. Please point out, what I should do differently:

Sparkfun BabyBuck AP63203 Voltage 3.3V.jpg
Sparkfun BabyBuck AP63203 Voltage 3.3V.jpg1362×828 207 KB

Result: I had sparks for half a second, but no fun.

After this “experiment”, I think, one Diode in the AP63203WU-7 (the 6-pin chip on the BabyBuck) died. The regulator was giving the same output Voltage of 12V on the supposed 3,3V output, as the input Voltage of 12V on VIN.

I wonder, how I should connect this BabyBuck Regulator Board to turn it on without MCU (to pull the EN pin high), as soon as I have 12V from the car battery coming in on VIN. The goal is to have a stable 3,3V output, as soon as there is 12V VIN present from the car battery.

As input Voltage, I have just the 12V line, coming from the car battery. I hope, that the Clock can run continuously with the “big” battery’s voltage around 12V, regulated down to 3,3V.

Currently, I run it with 2x1,5V AA-Batteries in series to get by with 3V for a longer time.

What solution do you recommend there? How would you connect the BabyBuck 3.3V (AP63203) to the 12V-Battery and 3v-clock to not have magic smoke?

Currently, I wonder, if I get a replacement BabyBuck-unit and some AP63203WU-7 chips to repair the fried regulator board.