MIC4930 datasheet(13/24 Pages) MICROCHIP

13 / 24 page

 2016 Microchip Technology Inc.

DS20005669A-page 13

MIC4930

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

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.

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