SNAU273 December   2022 LMX2820

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2SYNC Category
  5. 3SYNC Examples
    1. 3.1 Category 1 SYNC Example
    2. 3.2 Category 2 SYNC Example
    3. 3.3 Category 3 SYNC Example
  6. 4Other Considerations When Using SYNC
  7. 5References

2 SYNC Category

The requirements for phase synchronization depend on certain LMX2820 setup conditions. To use phase synchronization, first determine the SYNC category using the flow chart below.

Figure 2-1 SYNC Category Flow Chart

For Category 1 SYNC, there is no restriction at all. We do not need to enable SYNC mode (that is, we can keep register PHASE_SYNC_EN = 0). A SYNC signal is also not required.

In Category 2 SYNC, we must make PHASE_SYNC_EN = 1 and provide a SYNC signal to LMX2820. The SYNC signal is not time-critical, therefore a Low-to-High transition at the PSYNC pin is good enough.

When the LMX2820 configuration falls into Category 3 SYNC, we need both PHASE_SYNC_EN = 1 as well as a time-critical SYNC pulse. The setup and hold time of the SYNC pulse as specified in the data sheet must obey.

Figure 2-2 Time Critical SYNC Pulse

From the data sheet, the minimum tCS and tCH is 2.5 ns and 2 ns, respectively. Furthermore, the maximum fOSCIN is restricted to 200 MHz.

A reliable phase synchronization is not possible if the configuration of LMX2820 does not fall into the above categories.