SNAS816C March 2022 – February 2025 LMK5B33216
PRODUCTION DATA
If VDD or VDDO supplies are driven from different supply sources, TI recommends to start the PLL calibration after all of the supplies have ramped above 3.135V. This can be realized by delaying the PD# low-to-high transition. The PD# input incorporates a 200kΩ resistor to VDD_IN and as shown in Figure 9-2. A capacitor from the PD# pin to GND can be used to form an RC time constant with the internal pullup resistor. This RC time constant can be designed to delay the low-to-high transition of PD# until all the core supplies have ramped above 3.135V. Ramping the VDDO supply pins before the VDD supply pins is recommended.
Alternatively, the PD# pin can be driven high by a system host or power management device to delay the device power-up sequence until all supplies have ramped.
As described in Slow or Delayed XO Start-Up, the XO reference must be valid after PD# decision point 3 to provide a successful calibration of the VCOs and to capture a valid DPLL reference reading.