MIC24046-H Datasheet, PDF (11/24 Pages) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

Micrel, Inc.
The low-side current limit is programmable at three
different levels (3A, 4A, and 5A loads), in order to fit
different application requirements. Note that since the
low-side current limit acts on the valley current, the DC
output current level I_OUT at which the low-side cycle-by-
cycle current limit is engaged is higher than the current
limit value by an amount equal to ΔIL_PP/2, where ΔIL_PP is
the peak-to-peak inductor ripple current.
The high-side current limit is approximately 1.4 − 1.5
times bigger than the low-side current limit (typical
values). The high-side cycle-by-cycle current limit
immediately truncates the high-side ON time without
waiting for the OFF clocking event.
A leading-edge-blanking (LEB) timer (108ns, typical) is
provided on the high-side cycle-by-cycle current limit to
mask switching noise and to prevent false triggering of
the protection. Before the LEB timer has expired, high-
side cycle-by-cycle current limit action cannot take place.
Hiccup mode protection reduces power dissipation in
permanent short circuit conditions. On each clock cycle at
which a low-side cycle-by-cycle current limit event is
detected, a 4-bits up/down counter is incremented. On
each clock cycle without a concurrent low-side current
limit event, the counter is decremented or left at zero
(counter cannot wrap-around below 0000 and above
1111). Note that high-side current limit events do not
increment the counter, only low-side current limit event
detections do.
If the counter reaches 1111 (15 events), then the high-
and low-side MOSFETs are tri-stated and power delivery
to the output is inhibited for the duration of 3x the soft-
start time. This digital integration mechanism provides
immunity to momentary overloading of the output. After
the wait time, the MIC24046-H retries entering operation
and initiates a new soft-start sequence.
The flowchart of Figure 3 illustrates the hiccup mode
short-circuit protection logic flow. Note that hiccup mode
short-circuit protection is active at all times, including the
soft-start ramp.
July 7, 2015
11
MIC24046-H
Revision 1.1