SNVSBJ0A December 2019 – June 2020 LM5170
The LM5170 oscillator frequency is set by the external resistor ROSC connected between the OSC pin and AGND, as shown in Figure 31. The OSC pin must never be left open whether or not an external clock is present. To set a desired oscillator frequency FOSC, ROSC is approximately determined by Equation 17:
ROSC must be placed as close as possible to the OSC and AGND pins. Take the tolerance of the external resistor and the frequency tolerance indicated in the Electrical Characteristics table into account when determining the worst case operating frequency.
The LM5170 also includes a Phase-Locked Loop (PLL) circuit to manage multiphase interleaving phase angle as well as the synchronization to the external clock applied at the SYNCIN pin. When no external clock is present, the converter operates at the oscillator frequency given by Equation 17. If an external clock signal of a frequency within ± 20% of FSW is applied (see the Synchronization to an External Clock (SYNCIN, SYNCOUT) section), the converter will switch at the frequency of the external clock FEX_CLK, namely Equation 18:
Two internal clock signals CLK1 and CLK2 are produced to control the interleaving operation of CH-1 and CH-2, respectively. The third clock signal is output at the SYNCOUT pin. All these three clock signals run at the same frequency of FSW. The phase angles among these three clock signals are controlled by the state of the OPT pin. See the Multiphase Configurations (SYNCOUT, OPT) section for details.