SNAS689A October 2017 – July 2019 LMK04228
PRODUCTION DATA.
By programming MAN_DAC_EN = 0 and TRACK_EN = 1, the tracked voltage of CPout1 will be set on the CPout1 pin during holdover. When the DAC has acquired the current CPout1 voltage, the DAC_Locked signal is set which may be observed on Status_LD1 or Status_LD2 pins by programming PLL1_LD_MUX or PLL2_LD_MUX respectively.
Updates to the DAC value for the Tracked CPout1 sub-mode occurs at the rate of the PLL1 phase detector frequency divided by (DAC_CLK_MULT × DAC_CLK_CNTR).
The DAC update rate should be programmed for ≤ 100 kHz to ensure DAC holdover accuracy.
The ability to program slow DAC update rates, for example one DAC update per 4.08 seconds when using 1024-kHz PLL1 phase detector frequency with DAC_CLK_MULT = 16,384 and DAC_CLK_CNTR = 255, allows the device to look-back and set CPout1 at the previous good CPout1 tuning voltage values before the event which caused holdover to occur.
The current voltage of DAC value can be read back using RB_DAC_VALUE, see RB_DAC_VALUE.