When operating the LM5177 converters in multiphase operation the clock needs to be provided from external with a phase shift between the clock for the different Controller of 360 Degree or Number of Phases. Thus, the clock can be generated by different circuits, but in this implementation, the LMC555 timer device is used. This device is capable of producing a 3 MHz frequency. The LMC555 is designed to operate in the astable mode as shown in Figure 2-3. This mode generates a clock of a fixed frequency and duty cycle. The design includes a shunt diode with a resistor (R101) which improves the duty cycle of the clock signal. To change the frequency and duty cycle to a desired value, the proper value for C70, R85, and R101 need to be selected. Hence, the values shown in Figure 2-3 are selected to generate a frequency of 400 kHz with a duty cycle of 50%. A TLC555 Component Calculator Tool for the ease design of the clock generation circuit is available for download. The calculator is designed for the TLC555 device which supports 2 MHz frequency in astable mode, but the calculator can be used for all 555 timer devices with slight variation. For two-stage parallel operation, a simple LMC555 timer and inverter are enough like shown in the Figure 2-3.

Figure 2-3 2-Phase Clock Generator

For multi-phases in a parallel operation, a clock with a counter can be used as shown in Figure 2-4. The outputs of the clock source are connected to the SYNC pin of each LM5177 device to have a proper clock input.

Figure 2-4 Multiphase Clock Generator