SCY99194 Datasheet, PDF (18/40 Pages) ON Semiconductor – Fixed Frequency Current Mode Controller

SCY99194
The information about the fault (permanent Latch or
Autorecovery) is kept during the low consumption off mode
due the safety reason. The reason is not to allow unlatch the
device by the remote control being in off mode.
Start−up of the Controller
At start−up, the current source turns on when the voltage
on the HV pin is higher than V_HV(min), and turns off when
V_CC reaches V_CC(on), then turns on again when V_CC reaches
V_CC(min), until V_CC is supplied by an external source. The
controller actually starts the first time V_CC reaches V_CC(on)
when the slope on HV pin is positive.
Even though the Dynamic Self−Supply is able to maintain
the V_CC voltage between V_CC(on) and V_CC(min) by turning
VHV
the HV start−up current source on and off, it can only be used
in light load condition, otherwise the power dissipation on
the die would be too much. As a result, an auxiliary voltage
source is needed to supply V_CC during normal operation.
The Dynamic Self−Supply is useful to keep the controller
alive when no switching pulses are delivered, e.g. in latch or
fault condition, or to prevent the controller from stopping
during load transients when the V_CC might drop. The
SCY99194 accepts a supply voltage as high as 28 V, with an
overvoltage threshold V_CC(ovp) that latches the controller
off.
V HV(start)
V HV(min)
VCC
V CC(on)
V CC(min)
VCC(inhibit)
HV current
source = I_start1
DRV
Waits next VCC(on)
before starting
time
HV current
source = I_start2
time
Figure 43. V_CC Start−up Timing Diagram
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