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Problem in programming ADF4350

Question asked by vinayn on Apr 20, 2012
Latest reply on May 16, 2012 by vinayn

Hi, I want ADF4350 to generate frequencies from 1.1GHz to 1.3 GHz (sweep). I want a single frequency at a time. I am programming ADF4350 using a PIC microcontroller. Following are the details:

 

REFin = 16 MHz    (TXC oscillator; IC pin coupled through a 1 nF capacitor)

Rset = 5.1 k           Icp = 5 mA

Low noise mode     Cycle slip reuction DISABLED

Clock div mode OFF

 

Output frequency required : 1.1 GHz     FRAC-N synthesizer

output divider : 2                                  Feedback signal: Fundamental

Prescaler : 8/9

F_pfd = 16 MHz

Band select clock divider = 128             Ref doubler and divider OFF

R=1

MOD = 130  INT = 137   FRAC = 65

Register values R5 = 0x00 58 00 05

                        R4 = 0x 00 98 04 34

                        R3 = 0x 00 00 00 03

                        R2 = 0x 0C 00 5E 42

                        R1 = 0x 08 00 84 11

                        R2 = 0x 00 44 82 08

The loop filter is designed for a bandwith of 10kHz using ADIsimPLL. The pll file is attached.

Since the exact component values were not available, I have used near values:

C1 = 40.5nF -->47 nF

R1 = 81 --> 82

C2 = 550 nF --> 470 nF

R2 = 166 --> 180

C3 = 18.5 nF --> 22 nF

 

With all this I am not getting even the expected R counter output. The pulses are just flashing at the time of programming and are not retained.

I have checked the SPI waveforms on DSO. It looks fine.

 

I am totally clueless as how to go about this problem. In fact I am not getting where is the problem.

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