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Original question:

CD74HC14: CD74HC14E marking explanation

CD74HC14: CD74HC14 Oscillates on power up

Roy Bohlken
Prodigy 20 points

Part Number: CD74HC14

we have 

CD74HC14E with different marking 

32ACG7KE4   32ACFZKE4    2BA5ZGKE4  

3CA4QTMG4    3CA4QNMG4   3CA4QNMG4   

the parts ending with MG4 are have power up issues (see below) 

the parts ending with KE4 work ok 

schematic below is with through-hole parts and the MC have been changed to CD parts due to obsolescence

the circuit was design for a 2k hz oscillator

image.png

all unsed section inputs are grounded

5 volt supply

upper trace is Pin 1

green anf blue traces are 5 volts

 

image.png

bad

 

image.png

good

thanks for your help 

  • 0
    TI__Genius 10220 points

    Hi Roy,

    Have you considered using non-Schmitt Trigger devices such as SN74HCU04 in this design? You may have to adjust the values of your passive components slightly, but in addition to solving the power-up issues, it will switch at the exact same voltage instead of at different thresholds for positive-going and negative-going (see annotated image below).

    If you're committed to using a Schmitt Trigger device, SN74AHC14 would be better suited for this application.

    If you're willing to change your circuit topology slightly, I'd suggest moving away from the two-inverter oscillator because it's technically not stable. A good explanation of this can be seen on Page 3 of This App Note (see below for the relevant section). I would still suggest using non-Schmitt Trigger device for this.

    Regards,

    Nikki