ADF4351 datasheet(4/20 Pages) AD

4 / 20 page

UG-435

Evaluation Board User Guide

Rev. 0 | Page 4 of 20

EVALUATION BOARD HARDWARE

The EVAL-ADF4351EB1Z schematics are shown in Figure 22

to Figure 24.

POWER SUPPLIES

The EVAL-ADF4351EB1Z can be powered either from the USB

port or via dc power connectors (4 mm banana connectors).

When feeding via banana connectors, 3.75 V to 5.5 V is a

suitable feeding voltage. The power supply circuitry allows

the user to use one or two separate LDOs to feed the ADF4351

(using fewer LDOs increases the risk of spur contaminated dc

feeds). Consult the board schematic in Figure 22, Figure 23,

and Figure 24 to determine a suitable setting.

An LED, D6, indicates when USB power is available, and

another LED, D5, indicates when the ADF4351 is powered.

Switch S1 is used to power the ADF4351 from the external

dc connectors USB port and Switch S2 to power from the

USB port.

In case the USB processor or clock causes spurs on the RF

output signal, the user may feed the evaluation board via the

dc connectors and unplug the USB cable, thereby removing

power from the USB interface circuitry. There is also a

grounded frame surrounding the USB interface circuitry

to allow mounting of a shielding box.

INPUT SIGNALS

The 25 MHz TCXO from Rakon provides the necessary reference

signal. An external REFIN may be used if desired. In this case,

disable the on-board TCXO by removing L10 and R59. R9 can

be populated with 50 Ω to adjust impedance matching of the

evaluation board to the external reference source.

LOOP FILTER

The loop filter schematic is included in the board schematic on

Figure 22. The loop filter component placements are clarified in

Figure 2.

Figure 2. Loop Filter Placement

Figure 3. Evaluation Board Silkscreen

OUTPUT SIGNALS

The EVAL-ADF4351EB1Z has two SMA output connectors

(differential outputs). The device is quite sensitive to impedance

unbalance. If only one port of a differential pair is used,

terminate the other with a 50 Ω load.

The board contains 7.5 nH shunt inductors on the RF output

stages, which is optimum for a frequency range of 1 GHz to

4.4 GHz. Lower frequencies than this require larger output

stage inductors, or a 50 Ω resistor to VDD, which provides lower

output power, but wider frequency bandwidth than the

inductors. Consult the ADF4351 data sheet for more

information.

The MUXOUT signal can be monitored at the test point labeled

MUXOUT.

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