SN74HC14: Vol value shooting above vaues given in DS, need help.

Cashewmiro

Part Number: SN74HC14
Other Parts Discussed in Thread: LM2670, SN74AHC14, SN74HCS14, SN74LV14A

Tool/software:

Hello Team

I am using SN74HC14DR to give inputs coming into my board to a microcontroller. The Vcc is given through a regulated 5V power supply (LM2670).

As per datasheet I should be getting a VOL of max 0.33V but we are observing it comes to 0.730V in our case. As I mentioned the Vcc is 5V and the input to the individual schmitt trigger channels are around 4.5V.

Why could this be happening. Is there anything we need to consider? As an additional info : we are not observing this issue while using MC74HC14ADR2G in same application.

Thank You

2 months ago

0 Clemens Ladisch 2 months ago

Guru 289080 points

The output voltage depends on the output current. What is the load?

0 Cashewmiro 2 months ago in reply to Clemens Ladisch

Prodigy 20 points

Hello Clemens

The load current is coming as a maximum value of 5mA.

+1 Clemens Ladisch 2 months ago in reply to Cashewmiro

Guru 289080 points

I would expect such a V_OL with a 20 mA load. But MC74HC and SN74HC have the same drive strength, so it looks as if that chip got damaged. Have you tried replacing it?

With a 5 V supply, the V_OL of HC outputs is guaranteed only for up to 4.4 mA. The SN74HCS14, SN74AHC14, or SN74LV14A would haver stronger outputs.

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SN74HC14: Vol value shooting above vaues given in DS, need help.