PLL Operational Modes

CHETAN ASUNDI

What is the difference between PLL mode and Bypass mode in PLL? What is the function of PLL and PLL controller component in the PLL?

over 7 years ago

0 Alan O over 7 years ago

TI__Mastermind 32575 points

Are you asking this PLL about the DM355 specifically?

Alan

0 CHETAN ASUNDI over 7 years ago in reply to Alan O

Prodigy 100 points

Hi Alan
Not specifically. I need to know when and why do we use those two PLL modes on any chip
Chetan

0 Mukul Bhatnagar over 7 years ago in reply to CHETAN ASUNDI

TI__Guru* 84515 points

Please see if the simple explanations in one of our device PLL user guide helps
www.ti.com/.../sprugv2i.pdf

0 CHETAN ASUNDI over 7 years ago in reply to Mukul Bhatnagar

Prodigy 100 points

Hi Mukul

Thanks for your reply. I have already read the above document, but still I need to know the reason behind Bypassing. It would be helpful to know why do we do it?

Regards
Chetan

0 Mukul Bhatnagar over 7 years ago in reply to CHETAN ASUNDI

TI__Guru* 84515 points

The PLL bypass is usually not expected to be something that you would normally need to use when you are running the device "at speed" , to run a device at speed that is typically listed in the datasheet, it is going to be with PLL enabled and multiplier and dividers set to give you the VCO frequency need to run the device at speed.

PLL bypass is some time used when you want to run at low frequency e.g. for power savings, in such cases you can run the device at input clock frequency by not enabling aka bypassing the PLLs. Other times it is a good debug mechanism, some time due to device or board design issues you could run into issues where the PLL may not lock at speed etc, and having a bypass option allows you to debug the issues or run functional tests.

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PLL Operational Modes