LMX2615-SP: Can PLL_NUM exceed PLL_DEN?

Edwin Grigorian

Part Number: LMX2615-SP

Tool/software:

Does the LMX2615 automatically increment PLL_N whenever PLL_NUM is greater than PLL_DEN, or is it necessary for the controlling device to ensure that PLL_NUM always stays below PLL_DEN?

Ref. Eqn:

f_VCO = f_PD * (PLL_N + PLL_NUM / PLL_DEN)

7 months ago

0 Derek Payne 7 months ago

TI__Mastermind 32440 points

If PLL_NUM is ≥ PLL_DEN, PLL_NUM value is clamped to PLL_DEN, effectively giving f_VCO = f_PD * (PLL_N + 1).

0 Edwin Grigorian 7 months ago in reply to Derek Payne

Prodigy 20 points

Ok, so does that still hold true for PLL_NUM being multiples of PLL_DEN? e.g. if PLL_NUM / PLL_DEN = 3, then f_VCO = f_PD * (PLL_N + 3)?

0 Derek Payne 7 months ago in reply to Edwin Grigorian

TI__Mastermind 32440 points

Let me re-express:

f_VCO = f_PD * (PLL_N + min(PLL_NUM, PLL_DEN) / PLL_DEN)

Where PLL_DEN != 0

0 Edwin Grigorian 7 months ago in reply to Derek Payne

Prodigy 20 points

I see. So it will not handle multiples of PLL_NUM / PLL_DEN being greater than 1. We will need to modify our firmware to ensure that we keep this ratio less than or equal to 1. Thank you!

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LMX2615-SP: Can PLL_NUM exceed PLL_DEN?