ADF4001: Power supply requirements for Vp and AVDD

Question There are two power supplies for AVDD and Vp. If we shut down the Vp with AVDD still on, whether the part will be destroyed? If not, whether the current for AVDD will be larger than without Vp? Answer It is not acceptable for the Vp pin to be at a lower voltage than AVdd. Vp should always be greater than Vdd as there are diodes between these supplies. The diodes are to prevent Vp going below Vdd. So Vp should not be removed before Vdd.

ADF4001: phase difference between REF and RF output-2

Question If the output phase is different with the REF input phase, does it mean something wrong with the circuit? If the PLL is locked, the N*Fpfd (VCO output) should have the same phase with Fpfd*R (REF input) since the two inputs at PHASE DETECTOR should have the same frequency and the same phase. The R counter and N counter can not influence the phase. Is that correct? If so, I should check the loop filter and change a VCO, is there any other suggestions for solving this issue. Answer In lock status, if the voltage control side has a small impedance to the ground, there should be extra current from PLL pump charge to keep the loop stable. This extra current should be generated from phase difference. The result is in lock status, REF input and feedback input should keep a fixed phase difference, the smaller the impedance ,the larger the phase difference. There is another reason that may cause the problem, when using capacitor(i.e.Tantalum Capacitor) in the filter loop, there is small DC resistor or when using OP AMP to configurate an active filter, the input side has a small resistor to the ground. You could use the voltage of voltage control side and impedence of VCO to ground to calculate leakage current, then you know the phase difference of phase detector, the formular is as in figure2. This method could be used to troubleshoot the problem and by changing frequency and ICP to reduce phase difference. Phase delay caused by R and N counter can be ignored in most cases.

Replacing ADF4001 with ADF4002

The ADF4001 and ADF4002 are very similar. When replacing the ADF4001 with the ADF4002, there is no need for any hardware or register value changes, however, the initialization sequences for the two parts may be different. Consult the datasheet for more information.