ZHCSH13B October 2017 – January 2019 LMX2572
PRODUCTION DATA.
The LMX2572 requires an external loop filter that is application-specific and can be configured by PLLatinum Sim. For the LMX2572, it matters what impedance is seen from the Vtune pin looking outwards. This impedance is dominated by the component C3 for a third order filter or C1 for a second order filter. If there is at least 1.5 nF for the capacitance that is shunt with this pin, the VCO phase noise will be close to the best it can be. If there is less, the VCO phase noise in the 100-kHz to 1-MHz region will degrade. This capacitor should be placed close to the Vtune pin.