Two TPS7H500x-SEP controllers can be operated in a primary-secondary mode by utilizing the SYNC pin. As mentioned in Internal Oscillator Mode, when RT is selected to provide the desired switching frequency, SYNC outputs a clock signal at twice the switching frequency. As such, the clock input generated by the primary device could be used as the clock input at SYNC for the secondary controller, which would operate in external synchronization mode. This means that the RT pin of the primary device should be populated while the corresponding pin of the secondary device would be left floating.
The primary-secondary mode would be useful in a couple of scenarios. The first is for two independent converters that need to be synchronized to the same switching frequency. In this instance, the converters can be two converters can have different operating conditions or topologies. Besides the shared SYNC signal, there are no connections between the two converters.
In a second scenario, two controllers can be used to design a single interleaved converter with phases in parallel. In this design, the VSENSE, COMP, SS, and HICC pins would need to be connected in addition to the shared SYNC connection.
When using two controllers in primary-secondary mode, it is important to note that secondary controller will invert the clock signal that it receives from the primary controller. As such, there will be phase shift between the switching outputs of the primary and secondary controllers. This phase shift from an output (i.e. OUTA) on the primary controller to the corresponding output on the secondary controller will be 90° or 270°, depending on when the secondary device synchronizes to its clock input. Note that in Figure 8-12, the waveforms for OUTB are only applicable for TPS7H5005-SEP and TPS7H5008-SEP.
The three operational modes for the controller are summarized in Table 8-1.
|Internal oscillator||Populated with resistor to AVSS.||Configured as output. Generates in-phase clock at twice the switching frequency.||Configurable from 100 kHz to 2 MHz depending on RT value.|
|External synchronization||Floating.||Configured as input. Accepts 200-kHz to 4-MHz external clock that is inverted internally.||Synchronized to SYNC input clock at ½ of the clock frequency. Switching is out-of-phase with external clock.|
|Primary-secondary||Populated with resistor to AVSS on primary device. Floating on secondary device.||Configured as output on primary device. Configured as input on secondary device. The SYNC pins of primary and secondary devices are connected.||Configurable from 100 kHz to 2 MHz depending on RT value of primary device. Secondary device switching is either 90° or 270° out-of-phase with primary device.|