4 Operation Notes

To operate the test board using a single power supply, the VIN SELECT jumper (P1) must be in the default PVIN-VIN position as shown in Figure 2-1 and Figure 2-2. In this position, the PVIN and VIN pins of the LMZ31710 devices are connected together. When connected together the input voltage range is 4.5 to 17 V. Refer to the LMZ31710 10-A Module, 2.95-V to 17-V Input and Current Sharing in QFN Package data sheet for further information on the input voltage range, UVLO operation, and optional split power supply operation when using an external Vbias supply.

After a valid input voltage is present, the output voltage ramps to the selected value in approximately 1.2 ms. The soft-start time can be increased by adding a SS capacitor to the C12 position on the bottom of the test board. Refer to the LMZ31710 10-A Module, 2.95-V to 17-V Input and Current Sharing in QFN Package data sheet for further information on adjusting the soft-start time.

All LMZ31710 devices on the test board must be synchronized to the same frequency. This can be accomplished by either applying an external clock signal to the CLK_IN test point and running the clock to each device, or by setting the frequency of the controller device using the RRT resistor (R2) and running the Sync_Out signal to the remaining target devices. The Clock Phase Selector for each device is used to select either the external clock or the Sync_Out clock signal. The Sync_Out signal is a clock signal that is the same as the switching frequency, but is 180° out of phase. The test boards are set-up to operate at a free-running frequency of 300 kHz. To change the free-running switching frequency, the value of R2 can be changed according to the LMZ31710 10-A Module, 2.95-V to 17-V Input and Current Sharing in QFN Package data sheet.

Table 4-1 lists the switching frequency ranges for each of the VOUT selections. Several factors such as duty cycle, minimum on-time, minimum off-time, and current limit influence selection of the switching frequency.