CD74HC14: CD74HC14

The clamp diode characteristics. During the power up transistion, the Clamp diode drop is "LESS" and hence pulling VCC of IC to higher voltage level. This causes a failure in the unit level. The existing design was using a similar part from ONsemi MC74HC14AD,which doesnt causes this failure. The TI CD74HC14 was considered as FFF equivalent and went ahead with same design. 

hello 

I think i am having the same issue here                

Hi Abdelmajid,

Could you please provide more details as to your specific problem?

Best,

Ian

Hello  i got several CD74HC14E with different marking 

32ACG7KE4   32ACFZKE4    2BA5ZGKE4    Pass test

3CA4QTMG4    3CA4QNMG4   3CA4QNMG4    Fail test 

i used these chips in the same PCB with a socket. Based on the test results looks like any 3XXXXXMG4  is not passing the test

I have procured ONSEMI MC74HC14ADR2G and validated the same test case. The diode drop is more and works with power up sequence. 

Hi Vishal,

When you say the diode drop is more, do you have a higher input voltage than VCC on the device? This device is not rated for that. Could you give me a schematic?

Best,

Ian

Here is the section of Schematic.

The time delay of 5.5V_REF generation is 10msec after +5V_F. The counter IC (U11)output P_Q11 is pulling VCC of 74HC14 (5.5V_REF) through the clamp diode.  The issue was resolved by either adding current limit resistor R54=1K or by changing U12 to ONSEMI MC74HC14ADR2G.