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NCP1236AD65R2G

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NCP1236
www.onsemi.com
16
time
V
HV
time
V
CC
time
DRV
V
HV(start)
V
HV(min)
V
CC(on)
V
CC(min)
V
CC(inhibit)
HV
current
source =
I
start1
HV
current
source =
I
start2
Waits
next
V
CC(on)
before
starting
Figure 31. Start−up Timing Diagram
For safety reasons, the start−up current is lowered when
V
CC
is below V
CC(inhibit)
, to reduce the power dissipation in
case the V
CC
pin is shorted to GND (in case of V
CC
capacitor
failure, or external pull−down on V
CC
to disable the
controller).
There are only two conditions for which the current source
doesn’t turn on when V
CC
reaches V
CC(min)
: the voltage on
HV pin is too low (below V
HV(min)
), or a thermal shutdown
condition (TSD) has been detected. In all other conditions,
the HV current source will always turn on and off to maintain
V
CC
between V
CC(min)
and V
CC(on)
.
Brown−out protection
When the input voltage goes below V
HV(stop)
, a
brown−out condition is detected, and the controller stops.
The HV current source alternatively turns on and off to
maintain V
CC
between V
CC(on)
and V
CC(min)
until the input
voltage is back above V
HV(start)
.
NCP1236
www.onsemi.com
17
time
HV stop
time
V
CC
time
DRV
V
CC(on)
V
CC(min)
Waits next
V
CC(on)
before
starting
Brown-out
or AC OVP
detected
Figure 32. Brown−out Timing Diagram
When V
HV
crosses the V
HV(start)
threshold, the controller
can start immediately. When it crosses V
HV(stop)
, it triggers
a timer of duration t
HV
: this ensures that the controller
doesn’t stop in case of line cycle drop−out.
NCP1236
www.onsemi.com
18
time
V
HV
time
DRV
V
HV(start)
Starts at next
V
CC(ON)
V
HV(stop)
Brown-out
HV
t
Figure 33. AC Input Brown−out Timing Diagram
Oscillator with Maximum Duty Cycle and Frequency
Jittering
The NCP1236 includes an oscillator that sets the
switching frequency with an accuracy of $7%. Two
frequency options can be ordered: 65 kHz and 100 kHz. The
maximum duty cycle of the DRV pin is 80%, with an
accuracy of $7%.
In order to improve the EMI signature, the switching
frequency jitters $6% around its nominal value, with a
triangle−wave shape and at a frequency of 125 Hz. This
frequency jittering is active even when the frequency is
decreased to improve the EMI in light load condition.
Time
8%
(125 Hz)
Figure 34. Frequency Jittering
f
OSC
f
OSC
+ 6
Nominal f
OSC
f
OSC
− 6
Clamped Driver
The supply voltage for the NCP1236 can be as high as
28 V, but most of the MOSFETs that will be connected to the
DRV pin cannot accept more than 20 V on their gate. The
driver pin is therefore clamped safely below 16 V. This
driver has a typical current capability of $500 mA.
Figure 35. Clamped Driver
DRV
Clamp
DRV signal
VCC
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NCP1236AD65R2G

Mfr. #:
Buy NCP1236AD65R2G
Manufacturer:
ON Semiconductor
Description:
Switching Controllers BRWN LATCH OCP OVP 65KHZ
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
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