EVAL-AD7634 - External serial clock

Question

Hello, 
 I recently acquired an EVAL-AD7634 board and wish to operate it as stand-alone (serial slave mode), with a TI DSP TMS320F28335 as serial master. I would like to know if it's possible to provide the serial clock from the DSP to the ADC through the pin SCLK (connector P3 pin C7) . In page 3 of the related datasheet states that in this mode, SCLK (slave serial clock) = MCLK, which is a fixed clock frequency of 40MHz provided by oscillator U12. 
 Thanks in advance. 
 Gabriel Brunheira

ADIApproved · Accepted Answer

Hi Gabriel, 
 I think if you are using a discontinuous clock like with SPI then i would hook the SPI interface directly to the ADC and disconnect the FPGA. The FPGA MCLK is expecting to see a continuous clock. 
 Best Rgds, 
 Alan)

ADIApproved · Answer

Hi Gabriel, 
 You can get direct access to the ADC serial interface at the testpoints T3,T4,T5 but you may have to disconnect the traces from the gate array in order to get the desired slave functionality you want. I believe you are correct about the operation of the serial slave mode, this would prevent you driving the SCLK line directly with the DSP because of the onboard oscillator. 
 Best Rgds, 
 Alan

ADIApproved · Answer

Hi Gabriel, 
 You will have to cut the relevant traces to disconnect them from the FPGA or potentially change the FPGA code so they are high impedance and can be driven directly by your DSP. I think the 50 ohms to ground on CNVST is for termination so that the input signal has clean edges. You can remove them if your signal integrity looks good on the PCB. 
 Best Rgds, 
 Alan