LMX2595: RAMP, SPI and supply questions

Hello Aaron,

There are many ways to generate the 6 clocks, if you already have an input frequency you can use a buffer for this: https://www.ti.com/clocks-timing/buffers/overview.html.

If you do not have an input and need to generate one. Depending on the jitter you need to meet you can use a  low jitter clock generator (https://www.ti.com/clocks-timing/generators/overview.html) such as the LMK03318 or even a lower jitter BAW DPLL such as the LMK05318.

Finally if you need to provide a SYNC/SYSREF to align all the LMX2595s, clean up a dirty input clock with a jitter cleaner you could consider the LMK04xxx series (https://www.ti.com/clocks-timing/jitter-cleaners-synchronizers/products.html#p404=Dual-loop%20PLL;Cascaded%20PLLs).

Regarding the SPI bus:

If all the chips are going to be programmed to the same value, you can program them simultaneously. Perhaps you can program them to a specific starting point first and then program a few registers on each device to fine tune the VCO frequency, output dividers, etc. In any case you can use a microcontroller/FPGA to set the CSB pin high or low to selectively program certain devices.

If RAMPCLK and RAMPDIR are unused connect them to GND.

Yes, VccRF and Vcc can be from the same supply. Please refer to the LMX2595EVM schematic for an example.

Thanks,

Vibhu