JAJSMH6E July 2021 – August 2023 TPS7H5001-SP , TPS7H5002-SP , TPS7H5003-SP , TPS7H5004-SP
PRODMIX
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 TPS7H500x-SP controllers. During this mode, the primary outputs (OUTA/OUTB) will stop switching periodically. For the controllers with SR outputs, SRA/SRB remain on during pulse skipping if the soft-start period has ended. If the device enters into pulse skipping during the soft-start sequence, SRA/SRB remain off since the outputs are not yet active. 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.