LMX2491: N_DIVIDE

______健

Part Number: LMX2491

in the datasheet P9，I got this table, the minimum n divider is 16，what if i want to have a 200MHz PLL with a 200MHz VCO input to Fin？can N Divider set to 1 or there is another way？

Table 1. Allowable Minimum N Divider Values
MODULATOR ORDER MINIMUM N DIVIDE
Integer Mode, 1st-Order Modulator 16
2nd-Order Modulator 17
3rd-Order Modulator 19
4th-Order Modulator 25

over 5 years ago

0 Vibhu Vanjari over 5 years ago

TI__Genius 11900 points

Hello,

The VCO frequency must be at least 500 MHz.

Once your VCO frequency meets the requirement, you can decrease your phase detector frequency for a higher N value to meet the requirements in the datasheet.

Thanks,

Vibhu

0 ______健 over 5 years ago in reply to Vibhu Vanjari

Prodigy 80 points

if the VCO frequency is 500MHz，the max frequency of phase is 500/16=31.25MHz,that's much lower than 200MHz.And the response of the system can't not run as fast as that of 200MHz phase detector.I want the system run as fast as possible.Am I wrong about the response of the PLL system?

0 Vibhu Vanjari over 5 years ago in reply to ______健

TI__Genius 11900 points

Hello,

If you are worried about using a low phase detector frequency, the solution will be to use a bigger VCO frequency. Fin frequency can be up to 6400 MHz.

Thanks,

Vibhu

0 ______健 over 5 years ago in reply to Vibhu Vanjari

Prodigy 80 points

actually, I want a 500MHz signal ramp to 1.5GHz linearly.

0 Vibhu Vanjari over 5 years ago in reply to ______健

TI__Genius 11900 points

Hello,

Yes, this is possible. However do you have a VCO that extends across the whole range?

Thanks,

Vibhu

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LMX2491: N_DIVIDE