Proper way to switch on/off circuit using S9V11F5S6CMA regulator

Support Voltage regulators
1

HI all! Rather basic question here, I searched the forum but that did not turn up an answer.

I have a 7.4V LiPo --> S9V11F5S6CMA 5V regulator --> Arduino 5V pin.

Note that I connect to the Arduino’s 5V pin directly so I can bypass the Arduino’s very inefficient internal linear regulator. This does mean though, that I must make sure I never put anything above 5V on that pin or I’d fry the Arduino’s microcontroller.

As for the Arduino itself, it’s an AtMega microcontroller so it’s happy being switched on/off by simply having 0V or 5V on its 5V pin. But never more than 5V, or the magic smoke escapes.

The question is: what is the correct (safe) way to power on/off this circuit? Can I just have a open/close switch in the 7.4V line from the LiPo to the Pololu regulator Vin? Does the Pololu regulator make sure I don’t get anything above 5V on its Vout during power-up and power-down? Or do I need a more fancy solution?

Note that I don’t want to simply put a switch in the 5V to the Arduino because that way the regulator would still drain the LiPo quite fast with its 1mA no-load current (it’s a really tiny LiPo).

Thanks for your advice!

2

Hi.

It should be fine to use a switch between your battery and regulator. The S9V11F5S6CMA regulator (along with most of our other regulators) has a soft start feature that slowly ramps up the output voltage when the regulator is turned on, so you should not have to worry about overshooting 5V on startup. The regulator doesn’t have any specific feature for limiting the output voltage on shutdown, but I would not expect any spikes unless you are connecting something inductive (like a motor) to the Arduino 5V line.

-Claire

3

Thank you! That makes life easier. A reset of the Arduino might be needed afterwards, as ramping up the voltage can result in faulty booting the first time around. That’s fine in this project which isn’t commercial and needed an external reset button anyway.