I'm using LTC2174 on a FMC ADC board card. I want to program the mode control registers on LTC2174 which is SPI interface. But I can't get right readback data of registers(all bits are "1"). I'm not sure whether the ADC was set up properly.
So I made a test. Analog inputs of the ADC were not connected to signal. Then power on. The input clock (ENC+ and ENC-) was connected to a external clock (100MHz). I detected DCO of the ADC with Oscilloscope. The frequency of DCO was 133MHz. DCO is generated by PLL of LTC2174. I think that PLL didn't work fine and ADC were not set up properly. Because DCO frequency shouldn't so low with 100MHz input clock.
There are my questions:
1. Can I program mode control registers of LTC2174 without good working of the main part of the LTC2174? (ADC is with power and input clock)
2. How to set up LTC2174 properly? (For example, can I set up ADC only with power and input clock? The analog inputs must be connected to signal?)
If you bring the part up and provide a 100Mhz clock the DCo will be 400MHz, 2 lane 16 bit configuration. All you need is power and a clock and the ADC will output a DCO and a FRAME and data. Send a schematic of what you are doing and also a picture of the setup. How are you reading back the SDO lines?