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AD9548 REFA Not Valid

Question asked by angelsecop on Mar 7, 2017
Latest reply on Mar 8, 2017 by angelsecop

Good Morning,


I am using AD9548 IC but I am not able to get a valid reference. I need help, please.


I have programmed the free-running tunning word, the output drivers, and sync the output. At this point, the IC is acting like a frequency synthesizer. Then I have verified that the output frequency is indeed what I expect (200 MHz). This tells me that the system clock frequency is correct and stable. Value of the register 0x0D01 is 0x11.

Then, I have load the rest of the registers, issue and IO Update. The value of fast and slow in the register 0x0D0C is 1. So IC isn't detecting the signal on REFA (1PPS) at all.


The REFA signal is not AC coupled. After several configurations I put a 33 ohms resistor in REFA path in order to avoid ringing on the input signal. This avoid that the IC detects the REFA like a 2PPS or 3PPS signal.


 My configuration is the following:


- REFA: 1PPS (High Level 3.3V, Low Level 0V, Pulse Width 100ms and Edge Time 1us).


- 3 Outputs: 200 MHz LVDS, 50 MHZ LVCMOS, and 1PPS LVCMOS.

- I have attached my progile 0 file.

- System Clock lock and stable. Output is ok but register 0x0D0C is 0x87 (slow and fast are high)

- After put a 33 ohms resistor in the REFA path I got 0x80 in register 0x0D0C. fault and valid are low? I don't understand this.