In a typical application, TI recommends the following steps:
- Use the LMK5B12204 GUI in the TICS Pro programming software for a step-by-step design flow to enter the design parameters, calculate the frequency plan for each PLL domain, and generate the register settings for the desired configuration. The register settings can be exported (in hex format) to enable host programming or factory pre-programming.
- If using a generic (non-custom) device, a host device can program the register settings through the serial interface after power up and issue a soft-reset (by RESET_SW bit) to start the device. The host can also store the settings to the EEPROM to allow automatic start-up with these register settings on subsequent power-on reset cycles.
- Alternatively, a LMK5B12204 setup file for TICS Pro (.tcs) can be sent to TI to support factory pre-programmed samples.
- Tie the HW_SW_CTRL pin to ground to select EEPROM+I2C mode, or bias
the pin to VIM through the weak internal resistors or external
resistors to select EEPROM+SPI mode. Determine the logic I/O pin assignments for
control and status functions. See Section 6.1 for more information.
- Connect I2C/SPI and logic I/O pins (1.8-V
compatible levels) to the host device pins with the proper I/O direction
and voltage levels.
- Select an XO frequency by following Section 9.3.1 for more information.
- Choose an XO with target phase jitter performance that
meets the frequency stability and accuracy requirements required for the
output clocks during free-run or holdover.
- For a 3.3-V LVCMOS driver, follow the OSC clock
interface example in Figure 10-4. Power the OSC from a low-noise LDO regulator or optimize its power
filtering to avoid supply noise-induced jitter on the XO clock.
- TICS Pro: Configure the XO input buffer mode to
match the XO driver interface requirements. See Table 9-1 for more information.
- Wire the clock I/O for each PLL domain in the schematic and use TICS Pro to configure the device settings as follows:
- Reference inputs: Follow the LVCMOS or differential clock input interface
examples in Figure 10-4 or in Section 9.3.3.
- TICS Pro: For DPLL mode, configure the
reference input buffer modes to match the reference clock driver
interface requirements. See Table 9-2 for more information.
- LVCMOS clock input should be used for input
frequencies below 5 MHz when amplitude monitoring is
enabled.
- TICS Pro: For DPLL mode, configure the DPLL input selection modes and
input priorities. See Section 9.3.4 for more information.
- TICS Pro: If APLL2 is used, configure the APLL2 reference for VCO1 domain (Cascaded APLL2) or XO clock (Non-cascaded APLL2).
- TICS Pro: Configure each output with the required clock frequency and PLL domain. TICS Pro can calculate the VCO frequencies and divider settings for the PLL and outputs. Consider the following output clock assignment guidelines to minimize crosstalk and spurs:
- OUT[0:1] bank is preferred for PLL1 clocks.
- OUT[2:3] bank is preferred for PLL2 clocks.
- Group identical output frequencies (or harmonic frequencies) on adjacent channels.
- Separate clock outputs when the difference of the two frequencies, |fOUTx – fOUTy|, falls within the jitter integration bandwidth (12 kHz to 20 MHz, for example). Any outputs that are potential aggressors should be separated by at least four static pins (power pin, logic pin, or disabled output pins) to minimize potential coupling. If possible, separate these clocks by the placing them on opposite output banks, which are on opposite sides of the chip for best isolation.
- Avoid or isolate any LVCMOS output (strong aggressor) from other jitter-sensitive differential output clocks. If an LVCMOS output is required, use dual complementary LVCMOS mode (+/– or –/+) with the unused LVCMOS output left floating with no trace.
- If not all outputs pairs are used in the application, consider connecting an unused output to a pair of RF coaxial test structures for testing purposes (such as SMA, SMP ports).
- TICS Pro: Configure the output drivers.
- Configure the output driver modes to match the receiver clock input interface requirements. See Table 9-7 for more information.
- Configure any output SYNC groups that need their output phases synchronized.
See Section 9.3.15 for more information.
- Configure the output auto-mute modes, output mute levels, and APLL and DPLL
mute options. See Section 9.3.12.4 for more information.
- Clock output Interfacing: Follow the single-ended or differential clock output
interface examples in Figure 10-4 or in Section 9.3.14.
- Differential outputs should be AC-coupled and
terminated and biased at the receiver inputs.
- HCSL outputs should have 50-Ω termination to
GND (at source or load side) unless the internal source
termination is enabled by programming.
- LVCMOS outputs have internal source
termination to drive 50-Ω traces directly. LVCMOS VOH
level is determined by VDDO voltage (1.8 V).
- TICS Pro: Configure the DPLL loop bandwidth.
- Below the loop bandwidth, the reference noise is added to the TDC noise floor and the XO/TCXO/OCXO noise. Above the loop bandwidth, the reference noise will be attenuated with roll-off up to 60 dB/decade. The optimal bandwidth depends on the relative phase noise between the reference input and the XO. The loop bandwidth of the APLL1 can be configured to provide additional attenuation of the reference input, TDC, and XO phase noise above the bandwidth of the APLL1 (typically around 1 kHz).
- TICS Pro: Configure the maximum TDC frequency to optimize the DPLL TDC noise contribution for the desired use case.
- Wired: The maximum TDC rate is preset to 400 kHz. This supports SyncE and other use cases using a narrow loop bandwidth (≤10 Hz) with a TCXO/OCXO/XO to set the frequency stability and wander performance.
- Wireless: The maximum TDC rate is preset to 26 MHz for lowest in-band TDC noise contribution. This supports wireless and other use cases where close-in phase noise is critical.
- Custom: The maximum TDC rate can be specified for any value up to 26 MHz.
- TICS Pro: If clock steering is needed (such as for IEEE 1588 PTP),
enable DCO mode for the DPLL loop and enter the frequency step size (in
ppb). The FDEV step register will be computed according to Section 9.4.4.1. Enable the FINC/FDEC pin control on the GPIO pins, if needed.
- TICS Pro: Configure the reference input monitoring options for each
reference input. Disable the monitor when not required or when the input
operates beyond the supported frequency range of the monitor. See Section 9.3.7.2 for more information.
- Amplitude monitor: Set the LVCMOS detected slew
rate edge or the differential input amplitude threshold to monitor input
signal quality. Disable the monitor for a differential input below 5 MHz
or else use an LVCMOS input clock.
- Missing pulse monitor: Set the late window
threshold (TLATE) to allow for the longest expected input
clock period, including worst-case cycle-to-cycle jitter. For a gapped
clock input, set TLATE based on the number of allowable
missing clock pulses.
- Runt pulse monitor: Set the early window
threshold (TEARLY) to allow for the shortest expected input
clock period, including worst-case cycle-to-cycle jitter.
- Validation timer: Set the amount of time the
reference input must be qualified by all enabled input monitors before
the input is valid for selection.
- TICS Pro: Configure the DPLL lock detect and tuning word history
monitoring options for each channel. See Section 9.3.7.3 and Section 9.3.7.4 for more information.
- DPLL tuning word history: Set the history
count/averaging time (TAVG), history delay/ignore time
(TIGN), and intermediate averaging option.
- DPLL frequency lock and phase lock detectors:
Set the lock and unlock thresholds for each detector.
- TICS Pro: Configure each status output pin and interrupt flag as
needed. See Section 9.3.7.5 and Section 9.3.7.6 for more information.
- Select the desired status signal selection, status
polarity, and driver mode (3.3-V LVCMOS or open-drain). Open-drain
requires an external pullup resistor.
- If the Interrupt is enabled and selected as a status
output, configure the flag polarity and the mask bits for any interrupt
source, and the combinational AND/ OR gate as
needed.
- Consider the following guidelines for designing the power supply:
- Outputs with identical frequency or integer-related (harmonic) frequencies can share a common filtered power supply.
- Example: 156.25-MHz and 312.5-MHz outputs on OUT[0] and OUT[1] can share a filtered VDDO supply (Group 1), while 100-MHz, 50-MHz, and/or 25-MHz outputs on OUT[2:3] can share a separate VDDO supply (Group 2).
- For lowest power, AC-DIFF or HCSL outputs can be powered from a 1.8-V supply with no degradation in output swing or phase noise (compared to 2.5 V or 3.3 V).
- 1.8-V LVCMOS outputs should be powered from a 1.8-V supply.
- See Section 10.1.3.