# will this IC works with 3.3V digital signals

Discussion in 'General Electronics Chat' started by athulascc, Mar 15, 2015.

Aug 15, 2014
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2. ### DickCappels Moderator

Aug 21, 2008
3,830
1,042
It should work. If your Ardiuno controller and the SN74LVC2G157 both operate from a 3.3 volt supply and the 0 to 3.3 volt signal is digital.

3. ### athulascc Thread Starter Member

Aug 15, 2014
88
1
no
my ardiuno works with 5V
but I am going to switch using 5v ardiuno output

but my signal is 3.3V-0 it never connect with ardiuno
only I need to switch using ardiuno

will that works

4. ### DickCappels Moderator

Aug 21, 2008
3,830
1,042
If the control signal's peak voltage exceeds the power supply of the SN74LVC2G157 then you will have to do something to keep the current that might flow through the SN74LVC2G157's input from damaging the SN74LVC2G157 or the Arduiio directly or by causing the SN74LVC2G157 to go into SCR Latchup which is likely to destroy it.

It your control signal is 0 to 5 volts (the output of an Arudino controller with a 5V supply) and your multiplexer is connected to a 3.3 volt power supply and you do not need very high speed (hundreds of kHz or higher) then you can deal with the power supply difference by putting a 10k resistor between the Arduino output and the control input of the SN74LVC2G157

5. ### Papabravo Expert

Feb 24, 2006
11,083
2,159
The answers are right there in the datasheet. The input voltage can exceed Vcc if you do not exceed the input clamp current. The input clamp current will flow through the series resistor and be the output high voltage minus 3.3 V divided by the resistor value.

For example:
If the output high voltage is 4.8Volts and the resistor is 4.7K you would compute:
(4.8 -3.3) / 4700 ≈ 320 μA
I think you're safe there, chum!

It is also there in the feature list
Can Be Used as a Down Translator to Translate Inputs From a Max of 5.5 V Down to the VCC Level

Keep in mind that the threshold voltage is still determined by the Vcc to the 3.3V chip. If you ask me what the threshold voltage is I'm going to take a swing at you with a wet noodle.

Last edited: Mar 15, 2015
6. ### Arx&Sparx New Member

Feb 19, 2015
11
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For what it's worth, on Arduino, for the most part, the output pins will supply up to 40mA (i think it's for the 5VDC side). There is one voltage on the board that supplies 50mA (not sure which one).