Hi all,
Does anyone know of a low-power voltage detector chip that will not allow less than 5V to go to the Arduino Pro Mini's RAW pin? I'm trying to power a 5V Arduino Pro Mini with a 2S LiFePO4 battery (6.4V nominal). The Arduino will not be powered continuously, so it is possible that over a long period of time of not using the battery, the voltage could drop below 5V. How can I implement some small chip or diode so that the Arduino could not be powered if the voltage drops too low?
Thanks!
How about this part?
Will keep the supply at 5V with varying input. Connect to the VCC pin instead of RAW, bypass the onboard regulator.
CrossRoads, thank you for the response. It looks like this part could work. I don't completely understand what to do with the SHDN pin, however. I want to have a toggle switch that will cut all power from my battery, so that this regulator will be turned off when the switch is turned off. Then, when I turn the switch on, whatever voltage my batteries are at will go through this regulator and then power the Arduino Pro Mini. I don't think I need to use the SHDN pin for anything, but do I need to connect it to something so as to not leave it floating? I feel like if it's just floating, then it might want to power down?
Thanks.
Before you order that buck/boost converter, look at the efficiency at low-ish current, and the ~0.6mA draw in shutdown.
The ProMini's onboard 5volt regulator has a shutdown (enable) pin.
But... it's not available to the user without removing the smd chip and cutting the track underneath.
Google "UVLO chip" (UnderVoltageLockOut).
I didn't see anything worth mentioning, but you might have better luck.
Maybe you could measure battery voltage on startup, and choose "run" or "deep sleep".
Leo..
How about this then - cut off power from battery to regulator as well.
That chip seems like overkill for what I need. Also, the buck/boost converter does more than I need as well. I don't need a low battery voltage to be boosted to power the Arduino. Instead, I just want the power to be prevented from reaching the Arduino if the voltage is too low and could therefore damage the Arduino with a voltage outside of its operating range. Does the on-board voltage regulator do this automatically? As in, if the supplied voltage to the RAW pin is too low, will it recognize this and not try to power itself?
The board will never not power itself. If the voltage RAW is too low, the regulator output will be too low.
If the voltage VCC (the output of the regulator, of if applied directly) is below the Brownout Detector level (set by fuses), then a brown out reset will be asserted and the '328P chip won't start up.
A low supply voltage will not damage the Arduino. It will either not operate (brown out) or it may operate erratically (voltage too low per the Speed chart for the clock speed being operated at). It the internal clock is used at 1 MHz, or the clock divider fuses are set to operate at 1 MHz, then the voltage can be pretty low.
If you want power not to be applied if the supply voltage gets too low, then a low voltage detector controlling the Gate of a P-channel MOSFET is the way to go. That may be perhaps a N-channel MOSFET whose gate is driven by the supply voltage, when high enough it will turn on and bring the P-channel MOSFET gate low to turn it on.
Thank you for the in-depth explanation. Could you perhaps direct me to parts that seem compatible to you? I would greatly appreciate it.