ADF4372 datasheet(23/47 Pages) AD

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Data Sheet

ADF4372

Rev. 0 | Page 23 of 47

APPLICATIONS INFORMATION

POWER SUPPLIES

The ADF4372 contains four multiband VCOs that together cover

an octave range of frequencies. To achieve optimal VCO phase

noise performance, it is recommended to connect a low noise

regulator, such as the ADM7150 or LT3045, to the VCC_VCO

pin. Connect the same regulator to the VCC_VCO pin and the

VCC_LDO pin. It is recommended to connect 1 μF decoupling

capacitors to the 5 V VCO supply.

For all other 3.3 V supply pins, use one ADM7150 or one

LT3045 regulator. A 1 μF capacitor is also recommended for the

VDD_VP pin. Additional decoupling to other supply pins is not

required.

PCB DESIGN GUIDELINES FOR AN LGA PACKAGE

The bottom of the chip scale package has a central exposed

thermal pad. The thermal pad on the PCB must be at least as

large as the exposed pad. On the PCB, there must be a minimum

clearance of 0.25 mm between the thermal pad and the inner

edges of the pad pattern. This clearance ensures there is no

shorting

To improve the thermal performance of the package, use thermal

vias on the PCB thermal pad. If vias are used, incorporate them

into the thermal pad at the 1.2 mm pitch grid. The via diameter

must be between 0.3 mm and 0.33 mm, and the via barrel must

be plated with 1 oz. of copper to plug the via into the barrel.

For a microwave PLL and VCO synthesizer, such as the

ADF4372, take care with the board stackup and layout. Do not

consider using FR4 material because it causes an amplitude

decrease in signals greater than 3 GHz. Instead, Rogers 4350,

Rogers 4003, or Rogers 3003 dielectric material is suitable.

Take care with the RF output traces to minimize discontinuities

and ensure the best signal integrity. Via placement and grounding

are critical.

OUTPUT MATCHING

The low frequency output can be ac-coupled to the next circuit,

if desired. However, if higher output power is required, use a

pull-up inductor to increase the output power level.

7.5nH

10pF

RF8P

VDD_X1

50Ω

Figure 37. Optimum Output Stage

When differential outputs are not needed, terminate the unused

output or combine it with both outputs using a balun.

For lower frequencies that are less than 1 GHz, it is recommended

to use a 100 nH inductor on the RF8P pin and the RF8N pin.

The RF8P and RF8N pins form a differential circuit. Provide

each output with the same (or similar) components where

possible, including the same shunt inductor value, bypass

capacitor, and termination.

The RFAUX8P pin and the RFAUX8N pin are effectively the

same as the RF8P pin and the RF8N pin and must be treated in

the manner as outlined for the RF8P pin and the RF8N pin.

The RF16P pin and the RF16N pin can be directly connected to

the next circuit stage. These pins are internally matched to 50 Ω

and do not require additional decoupling.

ADF4372 Datasheet(PDF) 23 Page - Analog Devices

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