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Bleed current vs ramp generation

Category: Datasheet/Specs
Product Number: ADF4169

Hi

I need to generate ramp (fast ramp) with quite demanding requirements. Due to the ADsim simulation results, I need about 2MHz PLL filter band. With that band, bleed current is must be for single freq with integer mode.

I wonder, if "bleed current' is working during ramp generation and how it impact on the ramp?

The PLL filter may be design with almost the same parameters, but with different CP currents? I wonder, if there are any suggestion, that I should use high or low CP current with my design

I found one application note (AN-1154) about bleed current, but there is no info about ramp generation. Do you have any other papers?

Any suggestions?

  • Hi Roman, 

    Bleed current is useful when the sigma-delta modulator (SDM) is active for fractional N divider operation. It provides a constant current to the charge pump and helps to improve spurious performance. 

    The Datasheet provides bleed current calculations for optimum spurious performance at a certain frequency. However, smaller or larger bleed currents also provide improvement for SDM spurs. e 

    Ramp generation uses SDM to generate high-resolution ramps. Therefore we recommend using Bleed current to improve the SDM spurs.  I recommend selecting a middle point of the ramp frequency and then calculating the bleed current based on this frequency. 

    Thanks,

    Emrecan