SNAS824B October 2021 – June 2022 LMX2571-EP
PRODUCTION DATA
These register bits are used to define the calibration behavior. Correct setting is important to ensure that every F1-F2 switching time is optimized. Figure 8-6 illustrates the usage of these register bits.
Before t0: Device initialization
At t0: Locked to F1
After initialization, both F1 and F2 are calibrated. The calibration data is stored in the internal memory.
At t1: Switch to F2.
Because FCAL_EN = 1, calibration will start over again when the output is switching from F1 to F2. F2 calibration begins based on the last calibration data, which is the calibration data obtained at t0. If the environment (for example, temperature) does not change much, the new calibration data will be similar to the old data. As a result, the calibration time is minimal and therefore, the switching time will be short.
At t2: Switch back to F1
Again, F1 calibration starts over and begins with the last calibration data as obtained at t0. Calibration time is again very short, as is the switching time.
At t3: Switch again to F2
This time, the calibration begins with the calibration data obtained at t1, which is the last calibration data.
At t4: Switch back to F1
Calibration begins with the calibration data obtained at t2, which is the last calibration data.
At t5: Set new F1, F2 frequency
At t6: Locked to F1'
F1' and F2' calibration completed and their calibration data are ready.
At t7: Release F1F2_INIT bit
This bit has to be reset to zero or otherwise both F1' and F2' will be calibrated every time they are toggling.
At t8: F1' calibration data is updated
Since F1F2_INIT is located in register R0, when writing F1F2_INIT = 0 to the device, calibration is once again triggered. However, only F1' will be recalibrated, the calibration data of F2' remains unchanged.
At t9: Switch to F2'
F2' calibration begins with the calibration data obtained at t6, which is the last calibration data. Calibration time is again very short, as is the switching time.
At t10: Switch back to F1'
F1' calibration starts over and begins with the last calibration data as obtained at t8.
At t11: Switch again to F2'
The calibration begins with the calibration data obtained at t9, which is the last calibration data.
As illustrated above, register F1F2_INIT must be used properly in order to ensure that every F1-F2 switching time is optimized.