LMK00306: Crystal Interface - is feedback resistor needed?

Ella KIM

Part Number: LMK00306

Hi team,

I have a question on the OSCin/out configuration.

As in the figure above, usually for the crystal interface, there requires Rfb, feedback resistor, to bias the internal digital inverter to serve as an analog amplifier. (in the order of Mohm)

However, I cannot find Rfb in figure 28. Does LMK00306 require Rfb? Please help me get your response by EOD today. Thank you.

over 4 years ago

0 Noel Fung over 4 years ago

TI__Guru** 102620 points

Hi Ella,

Crystal interface of LMK00306 is design in the way that it does not require external feedback resistor.

0 Ella KIM over 4 years ago in reply to Noel Fung

TI__Expert 4172 points

Hi Noel,

Noel Fung said:
design in the way that it does not require external feedback resistor.

I guess the crystal interface is implemented in Pierce oscillator structure with CMOS inverter inside the IC. If so, does what you said mean that the feedback resistor is internal to IC?

+1 Aaron Black over 4 years ago in reply to Ella KIM

TI__Genius 10925 points

Hello Ella,

Yes, the crystal circuit structure utilizes internal bias structures to DC bias to the inverter block. There is no Rfd utilized in the structure. This is why the datasheet parameters should be followed when trying to match a crystal for this device application.

Hopefully this helps!

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LMK00306: Crystal Interface - is feedback resistor needed?