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Low Voltage Detection & Power Cut IC

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mikerj:

--- Quote from: JDW on August 28, 2019, 12:00:30 am ---
--- Quote from: mikerj on August 27, 2019, 03:57:54 pm ---If a microcontroller has no internal brownout/reset controller or a buggy/inadequate one then it's quite possible for a a micro to start doing unpredictable things during a slow supply voltage rise/fall, including executing from random bits of program memory that may contain the flash erase/write functions.
--- End quote ---

I don't think the Brown-out feature of my PIC16F1508 (which I am using) is "inadequate" but it applies to my PIC and not the Fingerprint Sensor.  it is the Fingerprint Sensor that, according to the manufacturer, needs to be powered off (since there's no way to easily "RESET" it) when the sensor's input voltage falls below 2.7V.

--- End quote ---

I am talking about the fingerprint sensor, which clearly has a micro inside it and it apparently doesn't behave well during slow power rise/fall times.

JDW:

--- Quote from: mikerj on August 30, 2019, 01:58:56 pm ---I am talking about the fingerprint sensor, which clearly has a micro inside it and it apparently doesn't behave well during slow power rise/fall times.

--- End quote ---

The fingerprint sensor has two MCU's inside it and a 3.0V regulator too, as shown in the following photo:

https://www.eevblog.com/forum/projects/low-voltage-detection-power-cut-ic/?action=dlattach;attach=820047;image

But I don't know what your specific recommendation to me is.  As I mentioned before, the pins are too tiny for me to expect a factory to hand-solder a teensy, tiny wire to the RESET pin(s) of the various ICs shown in the photo of the bottom of the fingerprint sensor.  As such, the only means of dealing with a brown-out situation would be for that detection to occur on my PIC board (separated from the fingerprint sensor by a 1.5 meter long set of cables, mind you), such that when the low voltage case is detected (say, 2.8V and less), then I would need some kind of circuit on my PIC board that would kill power completely to the fingerprint sensor until the voltage rises above that 2.8V threshold. I am just trying to figure out the best way to deal with all that in light of the 1.5 meter cable length.

Consider the5  wires in that 1.5 meter cable leading from my PIC and PSU board to the Fingerprint sensor:

1. +3.3V Power
2. GND
3. Tx (9600baud, rests at +3.3v, drops to 0v when sending data)
4. Rx (9600 baud, rests at +3.3v, drops to 0v when sending data)
5. +3.3v Analog Touch Wire (sends 3.3v from the sensor only while a finger is touching the metal frame of the sensor).

Adding some sort of ESD chip (with diodes and zener inside) on Tx & Rx would be needed with perhaps an inline 100-ohm or 200-ohm resistor with the PIC's Tx and Rx pints for protection, but protecting the other 3 pins is a bit more complex.  And to completely power off the fingerprint sensor I would need cut off all current flow to it, and that would require cutting 4 of the wires and leaving its GND intact.  Then add to that the need for brown-out detection and the means to cut all those wires too.  Any specific thoughts on a circuit to accomplish all that would be appreciated.

At least one person in another thread suggested I route higher voltage to the sensor, then build a tiny PSU board as a buck regulator to drop that voltage down to 3.3V for the sensor.  But the design requirements are such that there won't be space for such, and adding the needed protection circuitry for both 12V and 24V operation would make that tiny board not so tiny at all.  In other words, I have no choice but to run 3.3V from my PIC board to the fingerprint sensor.

Thank you!

TimNJ:
How about something like LM8364?

http://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Flm8364

JDW:

--- Quote from: TimNJ on August 31, 2019, 03:30:59 am ---How about something like LM8364?

http://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Flm8364

--- End quote ---

Thank you for your kindness in providing a link to a specific voltage reset IC.  I always appreciate specifics.

But as mentioned in my previous post, I need more than that. I need to find the best approach to not only detect the low voltage but also to cut power and protect.  Simply put, I need to:

1. Detect when voltage drops below 2.8v. (That's rather easy.)
2. Cut power to my fingerprint sensor (I assume the best way is to cut 4 of the 5 wires -- all but ground, but what is the best way to cut those 4 wires at once?)
3. Protect all 5 wires in light of the fact they connect via 1.5m cable.  ESD filtering on Tx and Rx alone would not be enough.  What if someone connects the 3.3V power line to ground?  What if someone cuts the wires and causes a short as a result of the cutting (at the instant the scissors touches all 5 wires at once)?

What is the best approach to this, do you think?

tautech:

--- Quote from: JDW on August 31, 2019, 06:03:36 am ---
--- Quote from: TimNJ on August 31, 2019, 03:30:59 am ---How about something like LM8364?

http://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=http%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Flm8364

--- End quote ---

Thank you for your kindness in providing a link to a specific voltage reset IC.  I always appreciate specifics.

But as mentioned in my previous post, I need more than that. I need to find the best approach to not only detect the low voltage but also to cut power and protect.

--- End quote ---
:-//
And you couldn't imagine to use the IC in reply #6 with a MOSFET and/or a quad logic switch like HEF4066B ?  :-/O

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