Hi, team.
My customer used SN74HC165-Q1 at Vdd = 5V.
But VIH will be over Vcc(about 16~36V).
There is no information in the datasheet as shown in the table below.
So My customer asked about VIH(max) when input voltage(VCC) is 5V.
Thank you!
Hi Charles,
We can't talk about input voltage without also talking about input current. The SN74HC165 will very likely be damaged by 16+V on the input -- assuming that the input current is not limited..
The absolute maximum ratings table indicates that there is a limitation on the input current, but not the input voltage:
Note that if the input voltage is greater than the supply, then the clamp diode will turn on and current will flow. This current must be limited to 20 mA or less.
It is best to limit the input voltage to Vcc to prevent this current from occurring at all, however it is possible to add a series resistance to the input to keep the clamp current low, and therefore the input voltage would remain in a safe region.
Hi Charles,
This device has diodes attached to each input known as "clamp diodes" or often just "clamps." These diodes prevent the input voltage from getting too high, so long as the current through them is limited.
There's a blog on this topic that explains it fairly well:
Please let me know if I can be of further assistance.
