NCP1217 ONSEMI [ON Semiconductor], NCP1217 Datasheet - Page 8
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NCP1217
Manufacturer Part Number
NCP1217
Description
Enhanced PWM Current−Mode Controller for High−Power Universal Off−Line Supplies
Manufacturer
ONSEMI [ON Semiconductor]
Datasheet
1.NCP1217.pdf
(18 pages)
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Introduction
architecture where the switch−off event is dictated by the
peak current setpoint. This component represents the ideal
candidate where low part−count is the key parameter,
particularly in low−cost AC/DC adapters, TV power
supplies, etc. Due to its high−performance High−Voltage
technology, the NCP1217 incorporates all the necessary
components normally needed in UC384X based supplies:
timing components, feedback devices, low−pass filter and
startup device but also enhances the original component
by
2) ramp
protection. Due to its high−voltage current source,
ON Semiconductor’s NCP1217 does not need an external
startup resistance but supplies the startup current directly
from the high−voltage rail. On the other hand, more and
more applications are requiring low no−load standby power,
e.g. for AC/DC adapters, VCRs, etc. UC384X series have a
lot of difficulty to reduce the switching losses at low power
levels. NCP1217 elegantly solves this problem by skipping
unwanted switching cycles at a user−adjustable power level.
By ensuring that skip cycles take place at low peak current,
the device ensures quiet, noise−free operation:
Current−Mode Operation: As the UC384X series, the
NCP1217 features a well−known current mode control
architecture which provides superior input audio−
susceptibility compared to traditional voltage−mode
controllers. Primary current pulse−by−pulse checking
together with a fast over current comparator offers greater
security in the event of a difficult fault condition, e.g. a
saturating transformer.
Ramp Compensation: By inserting a resistor between the
current−sense (CS) pin and the actual sense resistor, it
becomes possible to inject a given amount of ramp
compensation since the internal saw tooth clock is routed to
the CS pin. Subharmonic oscillations in Continuous
Conduction Mode (CCM) can thus be compensated via a
single resistor.
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 transformers. Skip cycle offers a
proven mean to reduce the standby power in no or light loads
situations.
Wide Switching−Frequency Offer: Three different options
are available: 65 kHz – 100 kHz–133 kHz. Depending on
the application, the designer can pick up the right device to
The NCP1217 implements a standard current mode
offering: 1) an externally triggerable latchoff
compensation
and
finally, 3) short−circuit
APPLICATION INFORMATION
NCP1217, NCP1217A
http://onsemi.com
8
help reducing magnetics or improve the EMI signature
before reaching the 150 kHz starting point.
Overcurrent Protection
monitoring the V
enters burst mode as soon as the power supply undergoes an
overload: when the V
the undervoltage lockout level (VCC
NCP1217 reaches this level (typically 7.6 V), it stops the
switching pulses until the V
(5.6 V). At VCC
soon as the default disappears, the power supply resumes
operation.
Overvoltage Protection (OVP): If pin1 is brought to a level
higher than the internal 3.2 V reference voltage, the
controller is permanently shut down until the user cycles the
VCC OFF and ON again. This allows the building of
efficient and low−cost over voltage protection circuits.
Wide Duty−Cycle Operation: Wide mains operation
requires a large duty−cycle excursion. The NCP1217 can go
up to 74% typically.
Low Standby−Power: If SMPS naturally exhibit a good
efficiency at nominal load, they begin to be less efficient
when the output power demand diminishes. By skipping
unneeded switching cycles, the NCP1217 drastically
reduces the power wasted during light load conditions. In
no−load conditions, the NPC1217 allows the total standby
power to easily reach next International Energy Agency
(IEA) recommendations.
No Acoustic Noise While Operating: Instead of skipping
cycles at high peak currents, the NCP1217 waits until the
peak current demand falls below a user−adjustable 1/3 of the
maximum limit. As a result, cycle skipping can take place
without having a singing transformer … You can thus select
cheap magnetic components free of noise problems.
External MOSFET Connection: By leaving the external
MOSFET external to the IC, you can select avalanche proof
devices, which in certain cases (e.g. low output powers), let
you work without an active clamping network. Also, by
controlling the MOSFET gate signal flow, you have an
option to slow down the device commutation, therefore
reducing the amount of ElectroMagnetic Interference
(EMI).
SPICE Model: A dedicated model to run transient
cycle−by−cycle simulations is available but also an
averaged version to help you closing the loop. Ready−to−use
templates can be downloaded in OrCAD’s Pspice and
INTUSOFT’s IsSpice from ON Semiconductor web site,
NCP1217 related section.
latch
CC
, the NCP1217 attempts to restart. As
auxiliary winding voltage, NCP1217
CC
voltage goes down until it crosses
CC
(OCP): By continuously
pin voltage reaches VCC
min
). When the
latch