MIC4930 Datasheet, PDF (13/24 Pages) Micrel Semiconductor – Hyper Speed Control 3A Buck Regulator

4.8 Hyper Speed Control^®
MIC4930 uses an ON- and OFF-time proprietary
ripple-based control loop that features three different
timers:
• Minimum ON Time
• Maximum ON Time
• Minimum OFF Time
When the required duty cycle is very low, the required
OFF time is typically far from the minimum OFF time
limit (about 176 ns typically). In this case, the MIC4930
operates by delivering a determined ON time at each
switching cycle, depending on the input voltage. A new
ON time is invoked by the error comparator when the
FB voltage falls below the regulation threshold. In this
mode, the MIC4930 operates as an adaptive
constant-ON-time ripple controller with nearly constant
switching frequency. Regulation takes place by
controlling the valley of the FB ripple waveform.
When higher duty cycles are required, regulation can
no longer be maintained by decreasing the OFF time
below the minimum OFF time limit. When this limit is
reached, the OFF time is no longer reduced, and the
MIC4930 smoothly transitions to an ON-time
modulation mode. In the ON-time modulation region,
frequency reduces with the increase of the required
ON-time / duty cycle, and regulation finally takes place
on the peak of the FB ripple waveform.
Note that because of the shift of the regulation
threshold between different modes, line regulation
might suffer when the input voltage and/or duty cycle
variations force the MIC4930 to switch form one
regulation mode to the other. In applications where
wide input voltage variations are expected, ensure that
the line regulation is adequate for the intended
application.
MIC4930
 2016 Microchip Technology Inc.
DS20005669A-page 13