SN54HCT04: Resistor selection for an oscillation circuit

George Zhao

Part Number: SN54HCT04
Other Parts Discussed in Thread: SN74AHCU04, CD4069UB

Hi team,

Is there any chance you have studied below circuit? On the left it is an LC oscillation circuit and in the middle it's an inverting buffer, competitor device is TC4069. When my customer change to SN54HCT04 they found the output waveform distorted. By changing the resistor, the waveform gets better.

I dont know how this circuit works, can you help explain why different device cause different output? Could it be because TC4069 is a CMOS device and SN54HCT04 is TTL ?

Thank you very much!

George

over 4 years ago

0 Dylan Hubbard over 4 years ago

TI__Mastermind 44665 points

Hi George,

The reason for the difference is due to the fact that the TC4069 contains unbuffered inverters which will have less gain than a normal inverters like the HCT04. I'd recommend using the SN74AHCU04 for this application, but the CD4069UB will closely match the performance of the previous device.

0 George Zhao over 4 years ago in reply to Dylan Hubbard

TI__Intellectual 1635 points

Hi Dylan,

Thanks for the reply.

How can I know if they are buffered or not? I didn't see them in datasheet.

Do you have any study material for me to learn more about this?

Thank you very much!

George

0 Dylan Hubbard over 4 years ago in reply to George Zhao

TI__Mastermind 44665 points

Hey George,

The unbuffered inverter function typically contains a 'U'. For example, AHCU04 vs the AHC04 which is a normal inverter. Also, it typically says in the title of the DS.

There is an app note that covers these types of parts: http://www.ti.com/lit/an/szza043/szza043.pdf

Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

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SN54HCT04: Resistor selection for an oscillation circuit