SLVSF07 July 2021 TPS7H5001-SP
In order to prevent converter operational issues related to the minimum on-time of the controller, specifically during high frequency operation, a pulse skipping mode has been implemented for the TPS7H5001-SP. During this mode, the primary outputs (OUTA and OUTB) will stop switching periodically. If the soft-start sequence of the converter has ended and the synchronous rectifier outputs are active, SRA and SRB will remain on during this period. If the device enters into pulse skipping during the soft-start sequence, SRA and SRB are not yet active and remain off. Having a minimum on-time that is too long in duration during high frequency operation can lead to an issue such as inductor current runaway during the soft-start period. Pulse skipping allows for overcoming this issue by reducing the peak inductor current during the startup period. In high frequency converter designs where the VIN to VOUT ratio of the converter may lead to required duty cycles that are less than the minimum on-time, the controller outputs will skip pulses in order to maintain the required output voltage. Pulse skipping will occur when both of the following conditions are present:
When the duty cycle limit of the controller is set to 50% and both OUTA and OUTB are active, the number of pulses skipped by each of the primary outputs will be equal. This will ensure the volt-second balance is maintained across the transformer and that flux-walking that leads to transformer saturation is avoided in isolated topologies such as the push-pull.