Another valuable circuit feature is an over-current
fault protection technique which provides fast
pulse-by-pulse current limiting with the ability to
accept a definable period of over-current operation
and then shut the system down if the fault is
continuous. Referring again to Figure 1, the Current
Limit pin is shown monitored by two comparators
with thresholds of 0.2 and 0.6 volts. (It
might be noted that noise filtering here has no
impact on the feedback control loop as it would
with current-mode control.) When the 0.2V
threshold is exceeded, the output is commanded
off within 100nsec. In addition, each time this occurs,
an increment of charge is added to the capacitor
on the COUNT pin and should the
voltage on this pin rise to 4V, a Shutdown Latch
is activated. This latch is also triggered immediately
if the current limit signal crosses the 0.6V
threshold. Reset of the Shutdown Latch occurs
when either VCC or VFWD falls below its lower
threshold which allow a variety of options for
either manual or automatic restart but, in either
case, reset initiates a normal soft-start.