LMK04906: Proper detection window size for PDF

Katsuhiko Kaizawa

Intellectual 2045 points

Part Number: LMK04906

Hello support team,

There was a problem that the PLL did not lock on LMK04906.

After that, when PLL1_WND_SIZE (R24[2: 1]) is changed from 40 ns to 5.5 ns, it is now locked.

It seems that the setting was inappropriate because the detection window setting was 40 ns for PLL1_PDF of 40 MHz, but how much is the detection window suitable for PDF?

Best regards,
Kaizawa

over 7 years ago

0 Timothy T over 7 years ago

TI__Mastermind 28590 points

Hello Kaizawa-san,

Yes, the period of 40 MHz is 25 ns. So a 40 ns window is unable to detect an in-lock condition with a phase detector rate of 40 MHz.

Did you find the 19 ns, and 10 ns window time also was able to lock?

73,
Timothy

0 Katsuhiko Kaizawa over 7 years ago in reply to Timothy T

TI__Intellectual 2045 points

Hi Timothy,

Thanks for your response.
I answered customer must set the window size within period of PDF.

Regards,
Kaizawa

Clock & timing

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LMK04906: Proper detection window size for PDF