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AD9578 problem

Question asked by cosmolittle on Nov 1, 2016
Latest reply on Nov 16, 2016 by SteveBeccue

At last I have finished my own development PCB and  software to program the AD9578 in rational mode. I can enter the frequency , and the software finds the minimum fractional divider,  minimum modulus, and output divider to generate the desired frequency. I can also read back the registers. I am currently using output1 and output2, both driven from PLL1. The outputs are set to LVPECL mode.

    Everything works, except that occasionally the output disappears from both outputs, and a power on reset is needed to restore normal function. Reading back the registers after this strange failure shows all the registers unchanged, with PLL1 still showing locked. The outputs are still LVPECL, with correct DC levels, however there is no AC output.

     The fault occurs from a few seconds to many minutes after power on reset and programming. After the failure, re-programming the registers has no effect.

    I am fairly sure that the power supplies are OK, with no glitches. If the chip was resetting, I would expect the registers to go back to the default, which they do not. When I program the chip, I first write to register2 with the MR bit set. I then write the correct data to register2 with the MR bit cleared. I then program all the other registers in order except registers 10,11,and 13. The following is the register data, starting with register1. note 32 bit registers have 2 trailing zeros, and 24bit registers 4 trailing zeros, etc.

 

PR
0000007A08000000
000000055F570000
0000001003000000
00000000AA000000
0000000000505000
0000003F000EA3DE
0000006474700401
000000000000000E
0000006460700400
0000000000000000
00000019DAAAA300
00000082AAAAAB00
00000026AA6AE200
00000003AAAAAA00
0000002600000000

 

The frequency is 39.96MHz, the fractional divider is 117, the modulus 125, the integer divider 63, and the output dividers 80.

S is 3.

 

I hope you can advise on this problem

 

best regards

 

Cosmo Little

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