Semiconductor Components Industries, LLC, 2005

October, 2005 - Rev. P0

Publication Order Number:

NCP1337/D

NCP1337

PWM Current-Mode
Controller for Free Running
Quasi-Resonant Operation

The NCP1337 combines a true current mode modulator and a

demagnetization detector which ensures full Borderline/Critical
Conduction Mode in any load/line conditions together with
minimum drain voltage switching (Quasi-Resonant operation). The
transformer core reset detection is done internally, without using any
external signal, due to the Soxyless concept. The frequency is
internally limited to 130 kHz, preventing the controller to operate
above the 150 kHz CISPR-22 EMI starting limit.

By monitoring the feedback pin activity, the controller enters

ripple mode as soon as the power demand falls below a
predetermined level. As each restart is softened by an internal
soft-start, and as the frequency cannot go below 25 kHz, no audible
noise can be heard.

The NCP1337 also features an efficient protective circuitry which,

in presence of an overcurrent condition, disables the output pulses
and enters a safe burst mode, trying to restart. Once the default has
gone, the device auto-recovers. Also included is a bulk voltage
monitoring function (known as brown-out protection), an adjustable
overpower compensation, and a V

OVP. Finally, an internal 4.0 ms

soft-start eliminates the traditional startup stress.

Features

Free-Running Borderline/Critical Mode Quasi-Resonant Operation

Current-Mode

Soft Ripple Mode with Minimum Switching Frequency for Standby

Auto-Recovery Short-Circuit Protection Independent of Auxiliary

Voltage

Overvoltage Protection

Brown-Out Protection

Two Externally Triggerable Fault Comparators (one for a disable

function, and the other for a permanent latch)

Internal 4.0 ms Soft-Start

500 mA Peak Current Drive Sink Capability

130 kHz Max Frequency

Internal Leading Edge Blanking

Internal Temperature Shutdown

Direct Optocoupler Connection

Dynamic Self-Supply with Levels of 12 V (On) and 10 V (Off)

SPICE Models Available for TRANsient and AC Analysis

These are Pb-Free Devices*

Typical Applications

AC-DC Adapters for Notebooks, etc.

Offline Battery Chargers

Consumer Electronics (DVD Players, Set-Top Boxes, TVs, etc.)

Auxiliary Power Supplies (USB, Appliances, TVs, etc.)

PDIP-7

P SUFFIX

CASE 626B

PIN CONNECTIONS

Device

Package

Shipping

ORDERING INFORMATION

NCP1337PG

PDIP-7

(Pb-Free)

50 Units/Tube

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MARKING
DIAGRAM

= Assembly Location

= Wafer Lot

Y, YY

= Year

= Work Week

= Pb-Free Package

(Top View)

GND

DRV

VCC

NCP1337P

AWL

YYWWG

SOIC-7

D SUFFIX

CASE 751U

NCP1337DR2G

SOIC-7

(Pb-Free)

2500 Tape & Reel

For information on tape and reel specifications,

including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specification
Brochure, BRD8011/D.

*For additional information on our Pb-Free strategy

and soldering details, please download the
ON Semiconductor Soldering and Mounting
Techniques Reference Manual, SOLDERRM/D.

P1337

AYWW

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PIN FUNCTION DESCRIPTION

Pin No.

Symbol

Function

Description

Brown-out and external
triggering

By connecting this pin to the input voltage through a resistor divider, the
controller ensures operation at a safe mains level.

If an external event brings this pin above 3.0 V, the controller's output is
disabled.

If an external event brings this pin above 5.0 V, the controller is
permanently latched-off.

Sets the peak current
setpoint

By connecting an optocoupler or an auxiliary winding to this pin, the peak
current setpoint is adjusted accordingly to the output power demand.

When the requested peak current setpoint is below the internal standby
level, the device enters soft ripple mode.

Current sense input and
overpower compensation
adjustment

This pin senses the primary current and routes it to the internal comparator
via an L.E.B.

Inserting a resistor in series with the pin allows to control the overpower
compensation level.

GND

IC ground

DRV

Output driver

To be connected to an external MOSFET.

VCC

IC supply

Connected to a tank capacitor (and possibly an auxiliary winding).

When V

reaches 18.6 V, an internal OVP stops the output pulses.

High-voltage pin

Connected to the high-voltage rail, this pin injects a constant current into
the V

bulk capacitor and ensures a clean lossless startup sequence.

NCP1337

Rcomp

bulk

OUT

Figure 1. Typical Application Schematic

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MAXIMUM RATINGS

Rating

Symbol

Value

Unit

Voltage on Pin 8 (HV) when Pin 6 (V

) is Decoupled to Ground with 10

-0.3 to 500

Maximum Current in Pin 8 (HV)

Power Supply Voltage, Pin 6 (V

) and Pin 5 (DRV)

CCmax

-0.3 to 20

Maximum Current in Pin 6 (V

)

Maximum Voltage on all Pins except Pin 8 (HV), Pin 6 (V

) and Pin 5 (DRV)

-0.3 to 10

Maximum Current into all Pins except Pin 8 (HV), Pin 6 (V

) and Pin 5 (DRV)

Maximum Current into Pin 6 (DRV) during ON Time and T

BLANK

1.0

Maximum Current into Pin 6 (DRV) after T

BLANK

during OFF Time

Thermal Resistance, Junction-to-Case

C/W

Thermal Resistance, Junction-to-Air, SOIC Version

178

C/W

Thermal Resistance, Junction-to-Air, DIP Version

100

C/W

Maximum Junction Temperature

MAX

150

Operating Temperature Range

-40 to +125

Storage Temperature Range

-60 to +150

ESD Capability, HBM Model per Mil-std-883, Method 3015 (All Pins except HV)

2.0

ESD Capability, Machine Model

200

Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values
(not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage
may occur and reliability may be affected.

1. This device contains latchup protection and exceeds 100 mA per JEDEC standard JESD78.

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ELECTRICAL CHARACTERISTICS

(For typical values T

= 25

C, for min/max values T

= 0

C to +125

C, Max T

= 150

= 11 V, unless otherwise noted.)

Characteristic

Pin

Symbol

Min

Typ

Max

Unit

SUPPLY SECTION

Increasing Level at which the Controller Starts

VCC

Decreasing Level at which the Controller Stops

VCC

MIN

9.0

Protection Mode is Activated if V

reaches this Level whereas the HV

Current Source is ON

VCC

OFF

9.0

Decreasing Level at which the Latch-Off Phase Ends

VCC

LATCH

3.6

5.0

6.0

Margin between V

Level at which Latch Fault is Released and

VCC

LATCH

MARGIN

0.3

Increasing Level at which the Controller Enters Protection Mode

VCC

OVP

17.6

18.6

19.6

Level below which HV Current Source is Reduced

VCC

INHIB

1.5

Internal IC Consumption, No Output Load on Pin 5, F

= 60 kHz

ICC1

1.2

Internal IC Consumption, 1.0 nF Output Load on Pin 5, F

= 60 kHz

ICC2

2.0

Internal IC Consumption, Latch-Off Phase, V

= 8.0 V

ICC3

600

Internal IC Consumption in Skip

ICC

LOW

600

INTERNAL STARTUP CURRENT SOURCE

Minimum Guaranteed Startup Voltage on HV Pin

HVmin

High-Voltage Current Source when V

> VCC

INHIB

= 10.5 V, V

= 60 V)

IC1

5.5

9.5

High-Voltage Current Source when V

< VCC

INHIB

= 0 V, V

= 60 V)

IC2

0.3

0.6

1.1

Leakage Current Flowing when the HV Current Source is OFF

= 17 V, V

= 500 V)

HVLeak

DRIVE OUTPUT

Output Voltage Rise-Time @ CL = 1.0 nF, 10-90% of Output Signal

Output Voltage Fall-Time @ CL = 1.0 nF, 10-90% of Output Signal

Source Resistance

Sink Resistance

8.0

TEMPERATURE SHUTDOWN

Temperature Shutdown

TSD

130

Hysteresis on Temperature Shutdown

CURRENT COMPARATOR

Maximum Internal Current Setpoint (@ I

= I

FB100%

)

CSLimit

475

500

525

Minimum Internal Current Setpoint (@ I

= I

FBrippleIN

)

CSrippleIN

100

Internal Current Setpoint for I

= I

FBrippleOUT

CSrippleOUT

130

Propagation Delay from Current Detection to Gate OFF State

DEL

120

150

Leading Edge Blanking Duration

LEB

350

Internal Current Offset Injected on the CS Pin during ON Time

(Over Power Compensation)

@ 1.0 V on Pin 1 and Vpin3 = 0.5 V
@ 2.0 V on Pin 1 and Vpin3 = 0.5 V

OPC

-
-

105

-
-

Maximum ON Time

MaxT

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ELECTRICAL CHARACTERISTICS

(continued) (For typical values T

= 25

C, for min/max values T

= 0

C to +125

Max T

= 150

C, V

= 11 V, unless otherwise noted.)

Characteristic

Pin

Symbol

Min

Typ

Max

Unit

FEEDBACK SECTION

FB Current under which FAULT is Detected

FBopen

FB Current for which Internal Setpoint is 100%

FB100%

FB Current above which DRV Pulses are Stopped

FBrippleIN

220

FB Current under which DRV Pulses are Reauthorized after having

reached I

FBrippleIN

FBrippleOUT

205

FB Current above which FB Pin Voltage is not Regulated anymore

FBregMax

500

FB Pin Voltage when I

FBopen

< I

FBregMax

2.8

3.0

3.2

Duration before Entering Protection Mode after FAULT Detection

FAULT

Internal Soft-Start Duration (Up to V

CSLimit

)

4.0

Internal Soft-Skip Duration (Up to V

CSLimit

)

SSkip

300

BROWN-OUT AND LATCH SECTION

Brown-Out Detection Level

460

500

540

Current Flowing out of Pin 1 when Brown-Out Comparator has Toggled

Vpin1 Threshold that Disables the Output

DISABLE

2.8

3.0

3.3

Vpin1 Threshold that Activates the Permanent Latch

LATCH

4.75

5.0

5.25

DEMAGNETIZATION DETECTION BLOCK

Current Threshold for Demagnetization Detection

SOXYth

210

Max Voltage on DRV Pin During OFF Time after T

BLANK

(when Sinking 15 mA)

DRVlowMAX

1.5

Min Voltage on DRV Pin During OFF Time after T

BLANK

(when Sourcing 15 mA)

DRVlowMIN

-0.6

Propagation Delay from Demag Detection to Gate ON State

GATE

Slope of 500 A/s)

DMG

180

220

Blanking Window after Gate OFF State before Detecting

Demagnetization

BLANK

5.5

Timeout on Demag Signal

OUT

8.0

Maximum OFF Time

MaxT

OFF

Minimum Switching Period

MinPeriod

6.8

7.5

8.2

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APPLICATION INFORMATION

INTRODUCTION

The NCP1337 implements a standard current mode

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, particularly in low-cost AC-DC adapters,
consumer electronics, auxiliary supplies, etc. Due to
its high-performance, high-voltage technology, the
NCP1337 incorporates all the necessary features needed to
build a rugged and reliable Switch-Mode Power Supply
(SMPS):

Quasi-Resonant Operation: Valley-switching
operation is ensured whatever the operating conditions
are, due to the internal soxyless circuitry. As a result,
there are virtually no primary switch turn-on losses,
and no secondary diode recovery losses, and EMI and
video noise perturbations are reduced. The converter
also stays a first-order system and accordingly eases
the feedback loop design.

Dynamic Self-Supply (DSS): Due to its Very High
Voltage Integrated Circuit (VHVIC) technology,
ON Semiconductor's NCP1337 allows for a direct pin
connection to the high-voltage DC rail. A dynamic
current source charges up a capacitor and thus
provides a fully independent V

level. As a result,

low power applications will not require any auxiliary
winding to supply the controller. In applications
where this winding is anyway required (see "Power
Dissipation" section in the application note), the DSS
will simplify the V

capacitor selection.

Overcurrent Protection (OCP): When the feedback
current is below minimum value, a fault is detected. If
this fault is present for more than 80 ms, NCP1337
enters an auto-recovery soft burst mode. All pulses are
stopped and the V

capacitor discharges down to

5.0 V. Then, by monitoring the V

level, the startup

current source is activated ON and OFF to create a
burst mode. After the current source being activated
twice, the controller tries to restart, with a 4.0 ms
soft-start. If the fault has gone, the SMPS resumes

operation. If the fault is still there, the burst sequence
starts again. The soft-start, together with a minimum
frequency clamp, allow to reduce the noise generated
in the transformer in short-circuit conditions.

Overvoltage Protection (OVP): By continuously
monitoring the V

voltage level, the NCP1337 stops

switching whenever an overvoltage condition is
detected.

Brown-Out Detection (BO): By monitoring the level
on Pin 1 during normal operation, the controller
protects the SMPS against low mains condition. When
Pin 1 level falls below 500 mV, the controller stops
pulsing until this level goes back and resumes
operation. By adjusting the resistor divider connected
between the high input voltage and this pin, start and
stop levels are programmable.

Over Power Compensation (OPC): An internal
current source injects out of Pin 3 (CS pin) a current
proportional to the voltage applied on Pin 1. As this
voltage is an image of the input voltage, by inserting a
resistor in series with Pin 3, it is possible to create an
offset on the current sense signal that will compensate
the effect of the input voltage variation.

External Latch Trip Point: By externally forcing a
level on Pin 1 (e.g., with a signal coming from a
temperature sensor) greater than 3.0 V (but below
5.0 V), it is possible to disable the output of the
controller. If the voltage is forced over 5.0 V, the
controller is permanently latched-off: to resume
normal operation, the V

voltage should go below

4.0 V, which implies to unplug the SMPS from the
mains.

Standby Ability: Under low load conditions,
NCP1337 enters a soft ripple mode: when the CS
setpoint becomes lower than 20% of the maximum
peak current, output pulses are stopped, then switching
is starting again when FB loop forces a setpoint higher
than 25%. As this occurs at low peak current, with
soft-skip activated, and as the T

OFF

is clamped,

noise-free operation is guaranteed, even with a cheap
transformer.

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Soxyless

The "Valley point detection" is based on the observation

of the Power MOSFET Drain voltage variations. When the
transformer is fully demagnetized, the Drain voltage
evolution from the plateau level down to the V

asymptote

is governed by the resonating energy transfer between the
L

transformer inductor and the global capacitance present

on the Drain. These voltage oscillations create current
oscillation in the parasitic capacitor across the switching

MOSFET (modelized by the Crss capacitance between
Gate and Drain): a negative current (flowing out of DRV
pin) takes place during the decreasing part of the Drain
oscillation, and a positive current (entering into the DRV
pin) during the increasing part.

The Drain valley corresponds to the inversion of the

current (i.e., the zero crossing): by detecting this point, we
always ensure a true valley turn-on.

Lprim

Crss

DRV

Isoxy

Vswitch

SWING

Figure 6. Soxyless Concept

The current in the Power MOSFET gate is:

Igate = Vringing/Zc (with Zc the capacitance impedance)
so
Igate = Vringing

S (2 S p S Fres S Crss)

The magnitude of this gate current depends on the

MOSFET, the resonating frequency and the voltage swing
present on the Drain at the end of the plateau voltage.

The dead time T

SWING

is given by the equation:

Tswing

0.5 Fres

+ p

* Lp * Cdrain

(eq. 1)

(where L

is the primary transformer inductance and

DRAIN

the total capacitance present on the MOSFET

Drain. This capacitance includes the snubber capacitor if
any, the transformer windings stray capacitance plus the
parasitic MOSFET capacitances C

OSS

and C

RSS

Internal Feedback Circuitry

To simplify the implementation of a primary regulation,

it is necessary to inject a current into the FB pin (instead of
sourcing it out). But to have a precise primary regulation,
the voltage present on FB pin must be regulated. Figure 8
gives the FB pin internal implementation: the circuitry
combines the functions of a current to voltage converter
and a voltage regulator.

3 V

Vdd

Internal
Setpoint

20 kHz

Low-pass Filter

Figure 7. Internal Implementation of FB Pin

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The input information is the current injected in FB pin by

the feedback loop. The range of current is from 40

mA for

overload detection to 220

mA corresponding to V

CSrippleIN

In transients, currents from 0 to more than 400

mA may also

appear: the circuitry is able to sustain them.

To regulate the FB pin voltage, the operational amplifier

needs to have a high gain and a wide bandwidth. But the
feedback information used internally needs to be filtered,
because we don't want the controller to be sensitive to the
switching noise. For this purpose, a 20 kHz filter is added
after the shunt regulator, and any reading of the feedback
signal (for ripple mode, fault detection, or setpoint
elaboration) is done after.

Soft Burst Mode (Protection Mode)

The NCP1337 features a fault timer to detect an overload

completely independently of the V

voltage. As soon as

the feedback loop asks for the maximum power, a fault is
detected, and an internal timer is started. When the fault
disappears the timer is reset, but if the timer reaches 80 ms,
the protection mode is activated.

Once this protection is toggled, output pulses are stopped

and DSS is deactivated (HV current source turn-on
threshold changes from VCC

MIN

to VCC

LATCH

). V

slowly decreases (the current consumption is ICC3), and
the HV current source is switched ON when V

reaches

VCC

LATCH

. As a result V

increases until VCC

, but the

controller does not start as the output is still forced low.
V

decreases again down to VCC

LATCH

, and a new

start-up cycle occurs. On the second attempt, the output is
released, and NCP1337 effectively starts, with the
soft-start activated. Figure 4 illustrates this behavior.

Safety Features

The NCP1337 includes several safety features to help the

power supply designer to build a rugged design:

OVP (Overvoltage on V

): Activated when voltage

on pin V

is higher than 18.6 V

Brown-Out (Undervoltage lockout on bulk voltage):
Activated when voltage on pin BO is below 500 mV

Disable (Comparator activated by an external signal):
Activated when the voltage on BO pin is higher than
3.0 V but below 5.0 V

TSD (Temperature shutdown): Typically activated
when the die temperature is above 150

°C, released at

120

°C

All these events have the same consequence for the

controller: the DRV pulses are stopped. When the condition
disappears, the controller restarts with the soft-start
activated.

Permanent Latch (Comparator activated by an external
signal): Activated when the voltage on BO pin is
above 5.0 V

When this comparator is activated, the DRV pulses are

stopped, and the DSS is deactivated (only the start-up

current source is turned on each time V

reaches

VCC

LATCH

, maintaining V

between 5.0 V and 12 V):

the controller stays in this position until the V

voltage is

decreased below 4.0 V, i.e., when the power supply is
unplugged from the mains (in normal operation, as soon as
a voltage is present on the HV pin, V

is always kept

above 5.0 V).

Soft Ripple Mode

The soft ripple mode is a skip mode with a large

hysteresis on the skip comparator in order to ensure a
noise-free and high-efficiency operation in low-load
conditions (standby). When internal setpoint is reaching
V

CSrippleIN

= 100 mV (corresponding to 20% of the

maximum setpoint), the output pulses are stopped. Then
FB loop asks for more power and internal setpoint is
increasing: when it reaches V

CSrippleOUT

= 130 mV

(corresponding to 25% of the maximum setpoint), the
output starts pulsing again. Soft-start is activated in each
activity following a stop period. See Figure 5 for detailed
timing diagram.

HV Current Source

NCP1337 features a DSS, to allow operation without any

auxiliary voltage. But to protect the die in case of
short-circuit on V

pin, the current delivered by the HV

current source is lowered when V

voltage is below 1.5 V.

In the case the current consumed on the DRV pin is

higher than the DSS capability (high Qg MOSFET or
failure), the HV current source is switched ON when V

reaches VCC

MIN

, but the voltage on V

pin keep on

decreasing. If there is no UVLO threshold to stop the DRV
pulses, the gate voltage will become too low and the risk is
high to destroy the MOSFET. NCP1337 features an
additional comparator, which threshold is 9.0 V: when V

reaches this level whereas the HV current source is ON,
DRV pulses are stopped and the protection mode is
activated.

Brown-Out

The brown-out protection comparator has a fixed

reference of 500 mV. When the comparator is activated
(i.e., when the input voltage V

is above the starting level),

a 10

mA internal current source is activated and creates an

offset across the bottom resistor of the external resistor
divider. It gives the minimum hysteresis of the brown-out
protection. By adding a series resistor between the divider
and the BO pin, it is possible to adjust (increase) the
hysteresis.

The BO pin also features two additional comparators: the

first one (that toggles at 3.0 V) stops the DRV pulses,
whereas the second one (that toggles at 5.0 V) permanently
latches off the controller (the V

should be forced below

4.0 V to release the latch).

Figure 8 gives the internal implementation of the BO

pin.

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ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any
liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental
damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over
time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under
its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body,
or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death
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PUBLICATION ORDERING INFORMATION

N. American Technical Support: 800-282-9855 Toll Free
USA/Canada

Japan: ON Semiconductor, Japan Customer Focus Center

2-9-1 Kamimeguro, Meguro-ku, Tokyo, Japan 153-0051
Phone: 81-3-5773-3850

NCP1337/D

The product described herein (NCP1337), may be covered by the following U.S. patents: 6,362,067, 5,073,850, 6,385,060, 6,587,357,
6,469,484, 6,940,320, 5,862,045. There may be other patents pending.

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