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ADF4155: Drops out of lock when temperature falls below -5 deg C

Question asked by MakeMyDay on Feb 2, 2016
Latest reply on Feb 4, 2016 by MakeMyDay

Hello,

I have a design using the ADF4155 that works very well at room temperature, but when I cycle temperature below freezing, lock is lost.  Probing with freeze-spray indicates when the chip is cooled (or the RF input line), lock is lost.  It returns spontaneously when the chip warms up again.  Has anyone seen this problem before (and know how to fix it)?  Does RF sensitivity shift much over temperature?  It does not appear to be a loop filter problem (cooling loop filter or VCO has no effect).  I also swapped out the ADF4155 chip for a new one and checked and rechecked the soldering.

 

The operating conditions are

 

Fref = 12MHz single ended 3V

Fosc = 6729MHz

VDD,VAA=3.2V

VP = 5V

Digital lock detect

 

  The programming words are given below (bytes are in natural order as shown in data sheet; i.e. last 4 bits of last byte in row are register addresses)

 

int LO1PLLData[9][4] = {{0x0, 0x10, 0x23, 0x0}, // Int value and prescale R0

                     {0xc, 0xf0, 0xf0, 0xf1},    // Frac1 value 13569807

                     {0x0, 0x0, 0x1, 0x12},      // MOD2 = 17

                     {0x0, 0x0, 0x0, 0x13}, // FRAC2 = 1

                     {0x30, 0x0, 0xc9, 0x84},

                     {0x0, 0x0, 0x0, 0x5},

                     {0x27, 0x80, 0x0, 0x46},

                     {0x0, 0x0, 0x2, 0x67},

                     {0xe, 0xa5, 0xfe, 0x18}}; //Phase word (large prime)

 

HELP! I am at my wits end and do not want to design in another chip.

 

Cheers and thanks!

Bill

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