NCP1234 ONSEMI [ON Semiconductor], NCP1234 Datasheet - Page 15

• Manufacturer Part Number: NCP1234
• Description: Fixed Frequency Current Mode Controller for Flyback Converters
• Manufacturer: ONSEMI [ON Semiconductor]

V
case the V
failure, or external pull−down on V
controller).
doesn’t turn on when V
HV pin is too low (below V
condition (TSD) has been detected. In all other conditions,
the HV current source will always turn on and off to maintain
V
quickly discharges, and the output starts to fall out of
CC
CC
For safety reasons, the start−up current is lowered when
There are only two conditions for which the current source
When the application is turned off, the input capacitor
is below V
between V
CC
pin is shorted to GND (in case of V
CC(inhibit)
CC(min)
V
V
V
CC(inhibit)
V
HV(min)
CC
CC(min)
and V
CC(on)
, to reduce the power dissipation in
DRV
V
reaches V
V
HV(min)
CC
HV
CC(on)
), or a thermal shutdown
.
CC(min)
CC
Figure 28. Start−up Timing Diagram
: the voltage on
to disable the
source =
current
CC
I
HV
start1
capacitor
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15
regulation. At the same time, V
is no voltage anymore on the HV pin, the DSS isn’t able to
turn on. As a result, V
V
internal fault timer, to prevent any unwanted latch−off and
allow a fast restart in case of a short OFF/ON sequence.
start−up current source starts to charge the V
Note that the threshold at which V
influence on the ability of the controller to restart. The
switching then turns on when V
additional delay or “hiccup”.The case of a fast OFF/ON
sequence is described at Figure 29.
CC(off)
As soon as the application is turned back on, the HV
source =
current
I
HV
start2
threshold, that turns the controller off, and resets the
CC
drops even more and reach the
CC
CC
time
time
time
reaches V
drops, but because there
CC
discharges has no
CC(on)
CC
capacitor.
, without