Circuit Note

CN-0232

Rev. 0 | Page 5 of 6

Initialization Procedure

The ADF4350 must go through the band select process for every

new frequency.

1. Initialize the ADF4350 as normal (program R5, R4, R3, R2,

because the ADF4350 charge pump is unused. Set DB9, R4 to

0 for divided VCO output on RFOUTB+. Enable RFOUTB+

(auxiliary out). This signal is fed to the ADF4153 over the

coax cable.

2. Initialize the ADF4153 (as per the data sheet) to accept the

VCO output frequency as the RF input frequency. Note

that the band select switch is internal; therefore, an external

3. When the ADF4153 achieves lock, the ADF4350 counter

reset to 1 (DB3, R2) must be activated. Not activating the

counter reset degrades spur performance. Additionally, all

ADF4350 synthesizer blocks can be powered down using

the test mode bit (DB10, R5).

Frequency Update

1. Program DB10, R5 to 0 to reactivate the ADF4350 synthesizer

blocks.

2. Program DB3, R2 of the ADF4350 to 0 to deactivate the

counter reset because these counters are required for band

select.

3. Program the ADF4350 and ADF4153 N-counter registers

as appropriate for the new frequency.

4. When the ADF4153 achieves lock, the ADF4350 counter

reset (DB3, R2) can be activated. Additionally all synthesizer

blocks can be powered down using the test mode bit

(DB10, R5).

5. Repeat Step 1 to Step 4 as required for new frequencies.

The software screen captures shown in Figure 5 and Figure 6 show

PFD (ADF4153).

After setting up the equipment, use standard RF test methods to

measure the spectral purity of the output signal.

Figure 5. ADF4350 Software Window

Figure 6. ADF4153 Software Window