Understanding limits of 16 channel multiplexer (CD74HC4067)

OBW0549

Joined Mar 2, 2015
3,566
...I'm having difficulty understanding what are the input limits of the actual signal pins. Are negative voltages allowed relative to ground? Would it pass small AC signals?
In the data sheet, look in the Operating Conditions section; this lists the DC Input or Output Voltage limits as 0V to Vcc. That is, inputs and outputs must always stay within the supply voltage range. The device will pass small AC signals, but only if they are offset with a DC bias so that the signal always stays within the allowed range.
 

Thread Starter

MikeA

Joined Jan 20, 2013
259
That is, inputs and outputs must always stay within the supply voltage range. The device will pass small AC signals, but only if they are offset with a DC bias so that the signal always stays within the allowed range.
That's what I was confused about, them calling it input and output, since the device is bi-directional.

Any idea why this device might not be -0.3v to Vcc tolerant? (Or least it's not specified.)
 

OBW0549

Joined Mar 2, 2015
3,566
Any idea why this device might not be -0.3v to Vcc tolerant? (Or least it's not specified.)
I always try to respect specified ratings, but it's hard for me to see anything catastrophic happening if you go just a few hundred millivolts below ground provided you limit the input/output current.
 

Papabravo

Joined Feb 24, 2006
16,829
That's what I was confused about, them calling it input and output, since the device is bi-directional.

Any idea why this device might not be -0.3v to Vcc tolerant? (Or least it's not specified.)
It lacks the protection diodes that offer that feature. The original part, designated CD4067 and CD4067B were from an original CMOS family (ca. 1973) that could operate from 3V to 18 V on Vcc. Those parts were extremely sensitive and had no protection diode. The CD74HC parts were a later series with a smaller Vcc range but otherwise compatible with the original part.
 

Thread Starter

MikeA

Joined Jan 20, 2013
259
It lacks the protection diodes that offer that feature.
So when a part is specified as -0.3v to Vcc is it safe to assume -0.4v won't kill the part as long as the protection diodes are not overloaded? In theory.

Is there a difference between "absolute maximum -0.3v to Vcc" and "operating range -0.3v to Vcc" when it comes to reading spec sheets?
 

dl324

Joined Mar 30, 2015
13,141
Is there a difference between "absolute maximum -0.3v to Vcc" and "operating range -0.3v to Vcc" when it comes to reading spec sheets?
Have you tried reading the datasheet? Devices aren't guaranteed to survive stressing beyond absolute max. In some cases, they aren't even guaranteed to survive absolute maximums.

From the datasheet:
clipimage.jpg
 
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