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I am looking to interface a 3.3V microcontroller (Raspberry Pi Pico) with many control voltages that can range from let's say -10V to 10V, but could also be 0 to 5V. I want to capture gate signals on the inputs, so this is a digital signal type with a frequency up to 10-20 kHz. So when an input signal goes higher than ~1V (could be slightly lower), then the microcontroller's input would go high (or low if the logic level is inverted).

The reason I am asking here is if anyone has a clever solution (maybe use ICs) to reduce the total part count since I will need something like 16 to 20 input signals that will need protection from the control voltages stated above which can easily require more than 100 components just to protect the inputs. Some common solutions for a single input can require some combination of a few resistors, diodes, and a transistor.

Example Input Protection(

Another example I dropped into my schematic

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  • \$\begingroup\$ Just for fun also read this. Or, in short, "Two long body resistors with a moat underneath them and a double-diode per pin, connected to a hard reference made with a properly biased power zener. Add a shield ground that is coupled with a ferrite bead to system ground. And for digital inputs add a schmitt fed from separate rail. If short high energy pulses, then plan to shunt using small caps to ground." Kind of annoying to consider. \$\endgroup\$
    – jonk
    Commented Jul 16, 2022 at 9:03

4 Answers 4

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If you want low parts count, you could always use use 74HC7014, hex schmitt trigger buffer, whose datasheet specifies that its inputs will survive "-1.5 V and +16 V without disturbing other channels." If you power it from 3V3 it will have standard LVCMOS input thresholds.

Another option would be the 164245 which does 16 lane voltage translation... I'm suggesting this one because it has 5V tolerant inputs and you can set VCC on the input side to 2V to get your 1V threshold. However the it does not have Schmitt trigger inputs.

So, from the input:

Resistor (perhaps a resistor network so you get multiple lanes with one part) to limit current ;

Multiple TVS diodes in the same package to clamp input voltage to -0.6V/+3V3 ;

Resistor again ;

Then to the input of the chip ;

Then to micro.

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Your '3904 circuit won't be reliable. With -10V inputs, the base-emitter junction of the transistor will breakdown (at about -6 V), and will degrade and ultimately destroy the transistor.

You could put a reverse-connected diode across the base-emitter to protect it -- an 1N4148 would work.

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Just use a series resistor, then clamping diodes e.g. BAT54S.

Resistor value needs to be high enough to limit input current, low enough for circuit purposes (a few mA into VDD would probably be dangerous, don't want to push more current into the rail than total load current, most likely), and low enough for whatever the source signal can deliver (source impedance is not defined so that's up to you), but not so high as to lose the signal across the input pin and diode capacitances (BAT54S dominates, 10pF or so, so for 20kHz, under 700kΩ say).

The input thresholds of an average MCU will be quite loose -- good enough for the stated 0/5V or -10/10V signals though.

If you need tighter thresholds, consider a typical logic analyzer front end: an array of comparators, with the reference voltage set by a single resistor divider, or DAC or something. Note that LVDS receivers can be used as comparators, but do mind the common mode input range; they aren't all created equally.

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Could be as simple as a resistor to limit current into the MCU pin. Most ICs can tolerate +/-1ma through the existing input protection….good parts even specify this.

Next consider mosfets which commonly tolerate +/- 20V with no additional protection (though esd protection is wise and some mosfets have it built in see NUD3112).

Buffer/Logic chips are another option.

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  • \$\begingroup\$ Do check, though. Don't just assume any old FET can handle 20 V on the gate. Many low-voltage MOSFETs have particularly thin gate oxide and can't handle more than around 8 to 12 volts on the gate. \$\endgroup\$
    – Hearth
    Commented Nov 25, 2023 at 3:31

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