Selecting a Buck Converter's Minimum On-Time

1. Put conversion ratio beside switching period

A buck-converter requirement can ask for a relatively low output from a higher input while also specifying a switching-frequency context. Those choices are connected through the high-side switching interval. The pulse must occupy an appropriate part of the switching period, so neither the requested conversion ratio nor a frequency headline completely describes the timing question on its own.

TI's minimum-on-time article explains that increasing switching frequency shortens the period available to accommodate the required pulse. A pulse that appears reasonable when considered only as a fraction of a period can still become too short for the selected converter's internal timing. This is why a nominal switching-frequency entry should not be treated as evidence of every input-output operating combination.

Consider a requirement covering more than one input condition. The relevant question is whether the converter can support the required pulse at each operating region that matters, especially a high-input, low-output situation. This is a qualitative selection question here. It does not calculate a duty cycle or establish a minimum pulse for an unidentified circuit.

2. Identify the device timing constraint

Minimum on-time describes a lower limit to the switching interval the converter can implement. TI relates that limit to internal switching and protection timing, rather than presenting it as a number that can be reduced without consequence. The important comparison is between the application's required operating region and the exact device's documented timing constraint.

Retain which pulse the specification describes. The article's discussion concerns high-side on-time; a general response-time or switching-speed claim is not the same field. Likewise, a high maximum operating frequency does not remove a minimum-on-time requirement. A candidate can have an attractive frequency description while still needing specific review at the requested input-output combination. The timing constraint also needs to be considered in the direction the application changes. A requirement moving toward a shorter pulse asks whether the lower limit is approached; it does not become complete by retaining the original nominal frequency. State which input-output region the comparison is intended to cover.

Read the limit in the candidate's own documentation instead of importing another converter's behavior. A smaller headline alone is not a complete selection decision, because the required operating region and the device's response at the limit still matter. The comparison should identify whether the limit is relevant, what evidence covers it and which behavior must be assessed when it is reached.

3. Separate skipped pulses from frequency reduction

TI describes pulse skipping as one possible response when on-time cannot be reduced further. Entire switching pulses are omitted in that explanation. The important point is that the pattern differs from an assumption that every nominal period contains a shorter pulse. A fixed-frequency headline would leave that change in behavior hidden if its applicable conditions were not retained.

The article also describes frequency foldback as a different response: switching frequency decreases while pulses continue regularly. That is not the same description as dropping whole pulses. Keep the exact candidate's documented response visible, rather than combining both under an unexplained lower-frequency label or assuming that every converter reaches its timing limit in the same way.

This question differs from choosing an intended light-load operating mode. The existing forced-PWM and pulse-skip guide concerns the selected mode and its load context. Here the trigger for review is a minimum-on-time constraint. Similar pulse-related vocabulary does not establish that a timing-limit response and a permitted light-load mode have the same cause, control mechanism or application consequence.

4. Review the affected operating region

Identify which input-output situations need the converter to preserve the application's switching behavior. A requirement that includes a frequency-sensitive subsystem needs to know whether minimum-on-time operation can change that behavior. TI's explanation makes that a legitimate selection question, but it does not demonstrate interference or compliance for the customer's equipment.

The engineering handover should distinguish three subjects: the requested operating region, the relevant pulse-width limit and the documented response at that limit. These subjects let the reviewer ask a specific question about an exact candidate. They also prevent an accepted light-load selection from being presented as the answer to an unrelated high-input, low-output timing issue.

A sourcing comparison can then identify whether each candidate supplies applicable evidence for those subjects. Do not replace missing limit behavior with an assumed waveform or an efficiency claim. No numerical recommendation follows from this guide, and no ripple or electromagnetic result is calculated. Its purpose is to expose a timing constraint that a catalogue frequency alone can conceal, while leaving actual circuit acceptance to its own assessment.

Sources and further reading

• Texas Instruments SSZTAH4 — How to Overcome Minimum On-time Challenges in Switching Power Supplies

TI SSZTAH4 physical pages 1–2 were reread as saved text on 15 October 2026. The qualitative pulse constraint and differing limit responses are used; no equations, waveform interpretation, numerical part choice or EMC result is supplied.