NCP1378 ON Semiconductor, NCP1378 Datasheet - Page 7

• Manufacturer Part Number: NCP1378
• Description: PWM Current-Mode Controller
• Manufacturer: ON Semiconductor

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architecture where the switch−off time is dictated by the
peak current setpoint, whereas the core reset detection
triggers the turn−on event . This component represents the
ideal candidate where low part−count is the key parameter
in applications supplied by a battery. Due to its high−
performance High−Voltage technology, the NCP1378
incorporates all the necessary components/features needed
to build a rugged and reliable Switchmode Power Supply
(SMPS):
The NCP1378 implements a standard current mode
Transformer Core Reset Detection: Borderline/critical
operation is ensured whatever the operating conditions
are. As a result, there are virtually no primary switch
turn−on losses and no secondary diode recovery
losses. The converter also stays a first−order system
and accordingly eases the feedback loop design.
Quasi−Resonant Operation: By delaying the turn−on
event, it is possible to restart the MOSFET in the
minimum of the drain−source wave, ensuring reduced
EMI/video noise perturbations. In nominal power
conditions, the NCP1378 operates in Borderline
Conduction Mode (BCM) also called Critical
Conduction Mode.
Undervoltage Lockout (UVLO): When V
below UVLO, all pulses are stopped and the IC
consumption drops down to a few hundreds of mA
(ICC3 data). When V
(5.5 V typical), the startup current source is activated
and brings V
to startup.
Overvoltage Protection (OVP): By sampling the
plateau voltage on the demagnetization winding, the
NCP1378 goes into latched fault condition whenever
an over−voltage condition is detected. The controller
stays fully latched in this position until the V
cycled down to 4.0 V, e.g. when the user unplugs the
power supply from the mains outlet and replugs it.
External LatchTrip Point: By externally forcing a
level on the OVP greater than the internal setpoint, it
is possible to latchoff the IC, e.g. with a signal coming
from a temperature sensor.
CC
back to VCC
INTRODUCTION
CC
reaches the latchoff level
ON
where the IC attempts
APPLICATION INFORMATION
CC
falls
CC
is
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NCP1378
7
VCC
Startup Sequence
outlet, the internal current source (typically 4.0 mA) is
biased and charges up the V
on this V
8.4 V), the current source turns off and no longer wastes
any power. At this time, the V
controller and the auxiliary supply is supposed to take over
before V
internal arrangement of this structure.
When the power supply is first powered from the mains
Adjustable Skip Cycle Level: By offering the ability
to tailor the level at which the skip cycle takes place,
the designer can make sure that the skip operation
only occurs at low peak current. This point guarantees
a noise−free operation with cheap transformer. This
option also offers the ability to fix the maximum
switching frequency when entering light load conditions.
Overcurrent Protection (OCP): NCP1378 enters burst
mode as soon as the power supply undergoes an
overload, which is detected through the sense of the
auxiliary voltage. As detailed above, as soon as V
crosses the UVLO level (called VCC
electrical table), all pulses are stopped and the device
enters a safe low power operation that prevents from
any lethal thermal runaway. By monitoring the V
level, the startup current source is activated ON and
OFF to create a kind of burst mode where the SMPS
tries to restart. If the fault has gone, the SMPS
resumes operation. On the other hand, if the fault is
still there, the burst sequence starts again.
Figure 15. The Current Source Brings Vcc Above
ON
/VCC-
CC
min
CC
collapses below V
capacitor reaches the VCC
Vcc
+
−
ON
and Then Turns Off
CC
CC
capacitor. When the voltage
CCmin
capacitor only supplies the
IC1 or 0
. Figure 15 shows the
8
6
4
ON
min
level (typically
in the
SVCC
HV
CC
CC
Aux