High-Voltage,
Quasi-Resonant, Controller
Featuring Valley Lock-Out
Switching
NCP1340
The NCP1340 is a highly integrated quasi−resonant flyback
controller suitable for designing high−performance off−line power
converters. With an integrated active X2 capacitor discharge feature,
the NCP1340 can enable no−load power consumption below 30 mW.
The NCP1340 features a proprietary valley−lockout circuitry,
ensuring stable valley switching. This system works down to the 6th
valley and transitions to frequency foldback mode to reduce switching
losses. As the load decreases further, the NCP1340 enters quiet−skip
mode to manage the power delivery while minimizing acoustic noise.
To help ensure converter ruggedness, the NCP1340 implements
several key protective features such as internal brownout detection, a
non−dissipative Over Power Protection (OPP) for constant maximum
output power regardless of input voltage, a latched overvoltage and
NTC−ready overtemperature protection through a dedicated pin, and
line removal detection to safely discharge the X2 capacitors when the
ac line is removed.
If transient load capability is desired, the NCP1341 offers the same
performance and features with the addition of power excursion mode
(PEM).
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Integrated High−Voltage Startup Circuit with Brownout Detection
Integrated X2 Capacitor Discharge Capability
Wide VCC Range from 9 V to 28 V
28 V VCC Overvoltage Protection
Abnormal Overcurrent Fault Protection for Winding Short Circuit or
Saturation Detection
Internal Temperature Shutdown
Valley Switching Operation with Valley−Lockout for Noise−Free
Operation
Frequency Foldback with 25 kHz Minimum Frequency Clamp for
Increased Efficiency at Light Loads
Skip Mode with Quiet−Skip Technology for Highest Performance
During Light Loads
Minimized Current Consumption for No Load Power Below 30 mW
Frequency Jittering for Reduced EMI Signature
Latching or Auto−Recovery Timer−Based Overload Protection
Adjustable Overpower Protection (OPP)
Fixed or Adjustable Maximum Frequency Clamp
Fault Pin for Severe Fault Conditions, NTC Compatible for OTP
4 ms Soft−Start Timer
© Semiconductor Components Industries, LLC, 2017
March, 2021 − Rev. 17
1
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8
9
1
1
SOIC−8 NB
D SUFFIX
CASE 751
SOIC−9 NB
D1 SUFFIX
CASE 751BP
MARKING DIAGRAM
9
1340xz
ALYW
G
1
1340xz
x
z
A
L
Y
W
G
= Specific Device Code
= A or B
= 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
PIN CONNECTIONS
Fault
1
HV
FB
VCC
ZCD/OPP
DRV
CS
GND
Fault
FMAX
FB
ZCD/OPP
CS
1
HV
VCC
DRV
GND
(Top Views)
ORDERING INFORMATION
See detailed ordering and shipping information on page 3 of
this data sheet.
Publication Order Number:
NCP1340/D
NCP1340
TYPICAL APPLICATION SCHEMATIC
Figure 1. NCP1340 8−Pin Typical Application Circuit
Figure 2. NCP1340 9−Pin Typical Application Circuit
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2
NCP1340
Table 1. ORDERING INFORMATION TABLE
Device Marking
Package
Shipping†
NCP1340A3D1R2G
1340A3
SOIC−9
2500 / Tape & Reel
NCP1340B1DR2G
1340B1
SOIC−8
2500 / Tape & Reel
NCP1340B3D1R2G
1340B3
SOIC−9
2500 / Tape & Reel
NCP1340B4D1R2G
1340B4
SOIC−9
2500 / Tape & Reel
NCP1340B5D1R2G
1340B5
SOIC−9
2500 / Tape & Reel
NCP1340A6DR2G
1340A6
SOIC−8
2500 / Tape & Reel
NCP1340B6DR2G
1340B6
SOIC−8
2500 / Tape & Reel
NCP1340B7D1R2G
1340B7
SOIC−9
2500 / Tape & Reel
NCP1340B8D1R2G
1340B8
SOIC−9
2500 / Tape & Reel
NCP1340B9D1R2G
1340B9
SOIC−9
2500 / Tape & Reel
NCP1340B10DR2G
1340B10
SOIC−8
2500 / Tape & Reel
Orderable Part Number
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
Table 2. DEVICE DIFFERENTIATION TABLE
Ordering Code
Brownout
Start/Stop
Levels
OVLD
Timer
X2
OTP/Overload
Protection
Frequency
Clamp
RFB
Pullup
VCC
OVP
IFB
Pullup
Jitter
NCP1340A3D1R2G
112V/98V
160 ms
Yes
Latched
Adjustable
400 kW
Yes
100 mA
1.3kHz
NCP1340B1DR2G
112V/98V
160 ms
Yes
Auto−Restart
None
400 kW
Yes
100 mA
1.3kHz
NCP1340B3D1R2G
112V/98V
160 ms
Yes
Auto−Restart
Adjustable
400 kW
Yes
100 mA
1.3kHz
NCP1340B4D1R2G
112V/98V
160 ms
Yes
Auto−Restart
Adjustable
20 kW
No
None
1.3kHz
NCP1340B5D1R2G
112V/98V
160 ms
Yes
Auto−Restart
Adjustable
20 kW
Yes
None
None
NCP1340A6DR2G
112V/98V
160 ms
Yes
Latched
None
20 kW
Yes
None
None
NCP1340B6DR2G
112V/98V
160 ms
Yes
Auto−Restart
None
20 kW
Yes
None
None
NCP1340B7D1R2G
112V/98V
160 ms
No
Auto−Restart
Adjustable
20 kW
Yes
None
None
NCP1340B8D1R2G
90V/80V
160 ms
No
Auto−Restart
Adjustable
20 kW
Yes
None
None
NCP1340B9D1R2G
90V/80V
40 ms
No
Auto−Restart
Adjustable
20 kW
Yes
None
None
NCP1340B10DR2G
Disabled
160 ms
No
Auto−Restart
None
20 kW
Yes
None
None
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3
NCP1340
FUNCTIONAL BLOCK DIAGRAM
Figure 3. NCP1340 Block Diagram
Table 3. PIN FUNCTIONAL DESCRIPTION
8−Pin
9−Pin
Pin Name
Function
1
1
Fault
The controller enters fault mode if the voltage on this pin is pulled above or below the fault
thresholds. A precise pull up current source allows direct interface with an NTC thermistor.
−
2
FMAX
A resistor to ground sets the value for the maximum switching frequency clamp. If this pin is
pulled above 4 V, the maximum frequency clamp is disabled.
2
3
FB
3
4
ZCD/OPP
4
5
CS
5
6
GND
Ground reference.
6
7
DRV
This is the drive pin of the circuit. The DRV high−current capability (−0.5 /+0.8 A) makes it suitable to effectively drive high gate charge power MOSFETs.
7
8
VCC
This pin is the positive supply of the IC. The circuit starts to operate when VCC exceeds 17 V and
turns off when VCC goes below 9 V (typical values). After start−up, the operating range is 9 V up
to 28 V.
−
9
N/C
Removed for creepage distance.
8
10
HV
This pin is the input for the high voltage startup and brownout detection circuits. It also contains
the line removal detection circuit to safely discharge the X2 capacitors when the line is removed.
Feedback input for the QR Flyback controller. Allows direct connection to an optocoupler.
A resistor divider from the auxiliary winding to this pin provides input to the demagnetization detection comparator and sets the OPP compensation level.
Input to the cycle−by−cycle current limit comparator.
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4
NCP1340
Table 4. MAXIMUM RATINGS
Rating
Symbol
Value
High Voltage Startup Circuit Input Voltage
VHV(MAX)
−0.3 to 700
V
High Voltage Startup Circuit Input Current
IHV(MAX)
20
mA
Supply Input Voltage
VCC(MAX)
−0.3 to 30
V
Supply Input Current (Note 1)
ICC(MAX)
30
mA
Supply Input Voltage Slew Rate
dVCC/dt
1
V/ms
Fault Input Voltage
VFault(MAX)
−0.3 to VCC + 0.7 V
V
Fault Input Current
IFault(MAX)
10
mA
Zero Current Detection and OPP Input Voltage
VZCD(MAX)
−0.3 to VCC + 0.7 V
V
Zero Current Detection and OPP Input Current
IZCD(MAX)
−2/+5
mA
VMAX
−0.3 to 5.5
V
Maximum Input Voltage (Other Pins)
Unit
Maximum Input Current (Other Pins)
IMAX
10
mA
Driver Maximum Voltage (Note 2)
VDRV
−0.3 to VDRV(high)
V
IDRV(SRC)
IDRV(SNK)
500
800
mA
Operating Junction Temperature
TJ
−40 to 125
°C
Maximum Junction Temperature
TJ(MAX)
150
°C
TSTG
–60 to 150
°C
Driver Maximum Current
Storage Temperature Range
Power Dissipation (TA = 25°C, 1 oz. Cu, 42
D Suffix, SOIC−8
D1 Suffix, SOIC−9
mm2
Copper Clad Printed Circuit)
Thermal Resistance (TA = 25°C, 1 oz. Cu, 42 mm2 Copper Clad Printed Circuit)
D Suffix, SOIC−8
D1 Suffix, SOIC−9
ESD Capability
Human Body Model per JEDEC Standard JESD22−A114F (All pins except HV)
Human Body Model per JEDEC Standard JESD22−A114F (HV Pin)
Charge Device Model per JEDEC Standard JESD22−C101F
Latch−Up Protection per JEDEC Standard JESD78E
PD(MAX)
RqJA
450
330
225
300
2000
800
1000
±100
mW
°C/W
V
V
V
mA
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. The VCC pin is rated to handle the full transient current of the DRV pin.
2. Maximum driver voltage is limited by the driver clamp voltage, VDRV(high), when VCC exceeds the driver clamp voltage. Otherwise, the
maximum driver voltage is VCC.
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5
NCP1340
Table 5. ELECTRICAL CHARACTERISTICS: (VCC = 12 V, VHV = 120 V, VFault = open, VFB = 2.4 V, VCS = 0 V, VZCD = 0 V, VFMAX
= 0 V, CVCC = 100 nF , CDRV = 100 pF, for typical values TJ = 25°C, for min/max values, TJ is – 40°C to 125°C, unless otherwise noted)
Characteristics
Conditions
Symbol
Min
Typ
Max
VCC(on)
VCC(on)
17.0
15.0
18.0
9.0
–
–
6.5
0.70
18.0
16.0
19.0
9.5
–
–
7.5
1.05
Unit
START−UP AND SUPPLY CIRCUITS
Supply Voltage
Startup Threshold (Other Versions)
Startup Threshold (Version B10)
Discharge Voltage During Line Removal
Minimum Operating Voltage
Operating Hysteresis (Other Versions)
Operating Hysteresis (Version B10)
Internal Latch / Logic Reset Level
Transition from Istart1 to Istart2
dV/dt = 0.1 V/ms
VCC increasing
VCC increasing
VCC decreasing
VCC decreasing
VCC(on) − VCC(off)
VCC(on) − VCC(off)
VCC decreasing
VCC increasing, IHV = 650 mA
VCC(X2_reg)
VCC(off)
VCC(HYS)
VCC(HYS)
VCC(reset)
VCC(inhibit)
16.0
14.0
17.0
8.5
7.5
5.5
4.5
0.40
VCC(off) Delay
VCC decreasing
tdelay(VCC_off)
25
32
40
ms
Startup Delay
Delay from VCC(on) to DRV Enable
tdelay(start)
–
–
500
ms
VHV(MIN)
–
–
30
V
0.2
0.5
0.65
mA
2.4
2.0
3.75
3.75
5.0
5.0
Minimum Voltage for Start−Up Current
Source
Inhibit Current Sourced from VCC Pin
Start−Up Current Sourced from VCC Pin
Start−Up Circuit Off−State Leakage Current
Supply Current
Fault or Latch
Skip Mode (excluding FB current)
Operating Current
V
Vcc = 0 V
Istart1
Vcc = Vcc(on) – 0.5 V
–40°C to 105°C
–40°C to 125°C
Istart2
VHV = 162.5 V
VHV = 325 V
VHV = 700 V
IHV(off1)
IHV(off2)
IHV(off3)
–
–
–
–
–
–
15
20
50
VCC = VCC(on) – 0.5 V
VFB = 0 V
fsw = 50 kHz, CDRV = open
ICC1
ICC2
ICC3
−
−
−
0.115
0.230
1.0
0.150
0.315
1.5
VCC(OVP)
27
28
29
V
tdelay(VCC_OVP)
25
32
40
ms
mA
mA
mA
VCC Overvoltage Protection Threshold
VCC Overvoltage Protection Delay
X2 CAPACITOR DISCHARGE (ALL VERSIONS EXCEPT B7/B8/B9/B10)
Line Voltage Removal Detection Timer
Discharge Timer Duration
Line Detection Timer Duration
VCC Discharge Current
VCC = 20 V
HV Discharge Level
tline(removal)
65
100
135
ms
tline(discharge)
21
32
43
ms
tline(detect)
21
32
43
ms
ICC(discharge)
13
18
23
mA
VHV(discharge)
–
–
30
V
107
85
112
90
116
95
93
75
98
80
102
85
9.0
6.0
14
10
–
–
BROWNOUT DETECTION (ALL VERSIONS EXCEPT B10)
System Start−Up Threshold
Other Versions
Versions B8, B9
VHV increasing
VBO(start)
V
Brownout Threshold
Other Versions
Versions B8, B9
VHV decreasing
Hysteresis
Other Versions
Versions B8, B9
VHV increasing
Brownout Detection Blanking Time
VHV decreasing
tBO(stop)
40
70
100
ms
Rise Time
VDRV from 10% to 90%
tDRV(rise)
–
20
40
ns
Fall Time
VDRV from 90% to 10%
tDRV(fall)
–
5
30
ns
VBO(stop)
V
VBO(HYS)
V
GATE DRIVE
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NCP1340
Table 5. ELECTRICAL CHARACTERISTICS: (VCC = 12 V, VHV = 120 V, VFault = open, VFB = 2.4 V, VCS = 0 V, VZCD = 0 V, VFMAX
= 0 V, CVCC = 100 nF , CDRV = 100 pF, for typical values TJ = 25°C, for min/max values, TJ is – 40°C to 125°C, unless otherwise noted)
Characteristics
Conditions
Symbol
Min
Typ
Max
IDRV(SRC)
IDRV(SNK)
–
–
500
800
–
–
Unit
GATE DRIVE
Current Capability
Source
Sink
mA
High State Voltage
VCC = VCC(off) + 0.2 V, RDRV = 10 kW
VCC = 30 V, RDRV = 10 kW
VDRV(high1)
VDRV(high2)
8.0
10
–
12
–
14
V
Low Stage Voltage
VFault = 0 V
VDRV(low)
–
–
0.25
V
VFB(open)
4.9
4.8
5.0
5.0
5.1
5.1
V
KFB
−
4
−
–
RFB
350
17
400
20
440
23
kW
IFB
90
−
100
0
108
−
mA
VFB decreasing
VFB decreasing
VFB decreasing
VFB decreasing
VFB decreasing
VFB increasing
VFB increasing
VFB increasing
VFB increasing
VFB increasing
V1to2
V2to3
V3to4
V4to5
V5to6
V6to5
V5to4
V4to3
V3to2
V2to1
1.316
1.128
1.034
0.940
0.846
1.410
1.504
1.598
1.692
1.880
1.400
1.200
1.100
1.000
0.900
1.500
1.600
1.700
1.800
2.000
1.484
1.272
1.166
1.060
0.954
1.590
1.696
1.802
1.908
2.120
VFMAX = 0.7 V
VFMAX = 3.5 V
VFMAX = 3.5 V
fMAX1
fMAX2
fMAX3
fMAX3
100
300
60
68
110
360
75
75
120
420
85
78
9−Pin Versions Only
VFMAX(mode)
3.85
4.00
4.15
V
IFMAX
9.0
10
11
mA
ton(MAX)
28
32
40
ms
FEEDBACK
Open Pin Voltage
Versions B5/B6/A6
VFB to Internal Current Setpoint Division
Ratio
Internal Pull−Up Resistor
Versions A6, B4, B5, B6, B7, B8, B9, B10
VFB = 0.4 V
Internal Pull−Up Current
Versions A6, B4, B5, B6, B7, B8, B9, B10
Valley Thresholds
Transition from 1st to 2nd valley
Transition from 2nd to 3rd valley
Transition from 3rd to 4th valley
Transition from 4th to 5th valley
Transition from 5th to 6th valley
Transition from 6th to 5th valley
Transition from 5th to 4th valley
Transition from 4th to 3rd valley
Transition from 3rd to 2nd valley
Transition from 2nd to 1st valley
Maximum Frequency Clamp
Versions A2, B2
Versions A3, B3, B4, B5, B7, B8, B9
Versions A3, B3, B5, B7, B8, B9
Version B4
FMAX Secondary Mode Threshold
V
FMAX Pin Source Current
Maximum On Time
kHz
DEMAGNETIZATION INPUT
ZCD threshold voltage
VZCD decreasing
VZCD(trig)
35
60
90
mV
ZCD hysteresis
VZCD increasing
VZCD(HYS)
15
25
55
mV
VZCD step from 4.0 V to −0.3 V
tdemag
–
80
250
ns
IQZCD = 5.0 mA
IQZCD = −2.0 mA
VZCD(MAX)
VZCD(MIN)
12.4
−0.9
12.7
−0.7
13
0
Demagnetization Propagation Delay
ZCD Clamp Voltage
Positive Clamp
Negative Clamp
V
Blanking Delay After Turn−Off
tZCD(blank)
600
700
800
ns
While in soft−start
After soft−start complete
t(tout1)
t(tout2)
80
5.1
100
6.0
120
6.9
ms
Current Limit Threshold Voltage
VCS increasing
VILIM1
0.760
0.800
0.840
V
Leading Edge Blanking Duration
DRV minimum width minus
tdelay(ILIM1)
tLEB1
220
265
330
ns
Timeout After Last Demagnetization
Detection
CURRENT SENSE
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NCP1340
Table 5. ELECTRICAL CHARACTERISTICS: (VCC = 12 V, VHV = 120 V, VFault = open, VFB = 2.4 V, VCS = 0 V, VZCD = 0 V, VFMAX
= 0 V, CVCC = 100 nF , CDRV = 100 pF, for typical values TJ = 25°C, for min/max values, TJ is – 40°C to 125°C, unless otherwise noted)
Characteristics
Conditions
Symbol
Min
Typ
Max
Unit
Step VCS 0 V to VILIM1 + 0.5 V,
VFB = 4 V
tdelay(ILIM1)
–
95
175
ns
Step VCS 0 V to 0.7 V, VFB = 2.4
tdelay(PWM)
–
125
175
ns
Vfreeze
170
200
230
mV
CURRENT SENSE
Current Limit Threshold Propagation Delay
PWM Comparator Propagation Delay
Minimum Peak Current Freeze Setpoint
Abnormal Overcurrent Fault Threshold
VCS increasing, VFB = 4 V
VILIM2
1.125
1.200
1.275
V
Abnormal Overcurrent Fault Blanking
Duration
DRV minimum width minus
tdelay(ILIM2)
tLEB2
80
110
140
ns
Step VCS 0 V to VILIM2 + 0.5 V,
VFB = 4 V
tdelay(ILIM2)
–
80
175
ns
nILIM2
–
4
–
tOPP(delay)
–
95
175
ns
tOPP(blank)
220
280
330
ns
ICS
0.7
1.0
1.5
mA
Jitter Frequency
fjitter
1.0
1.3
1.6
kHz
Peak Jitter Voltage Added to PWM
Comparator
Vjitter
90
100
115
mV
Measured from
1st DRV pulse to VCS = VILIM1
tSSTART
2.8
4.0
5.0
ms
VCS = VILIM1
tOVLD
120
30
160
40
200
50
Overvoltage Protection (OVP) Threshold
VFault increasing
VFault(OVP)
2.79
3.00
3.21
V
OVP Detection Delay
VFault increasing
tdelay(OVP)
22.5
30
37.5
ms
Overtemperature Protection (OTP)
Threshold (Note 3)
VFault decreasing
VFault(OTP_in)
380
400
420
mV
Overtemperature Protection (OTP) Exiting
Threshold (Note 3)
VFault increasing
Versions B Only
VFault(OTP_out)
874
910
966
mV
OTP Detection Delay
VFault decreasing
tdelay(OTP)
22.5
30
37.5
ms
VFault = VFault(OTP_in) + 0.2 V
IOTP
42.5
45.0
48.5
mA
Fault Input Clamp Voltage
VFault(clamp)
1.15
1.7
2.25
V
Fault Input Clamp Series Resistor
RFault(clamp)
1.32
1.55
1.78
kW
trestart
1.8
2.0
2.2
s
fMIN
21.5
25
27.0
kHz
tDT(MAX)
34
−
−
ms
tquiet
1.25
−
−
ms
Abnormal Overcurrent Fault Propagation
Delay
Number of Consecutive Abnormal Overcurrent Faults to Enter Latch Mode
Overpower Protection Delay
VCS dv/dt = 1 V/ms, measured from
VOPP(MAX) to DRV falling edge
Overpower Signal Blanking Delay
Pull−Up Current Source
VCS = 1.5 V
JITTERING (All Except Version A6, B5, B6, B7, B8, B9, B10)
FAULT PROTECTION
Soft−Start Period
Flyback Overload Fault Timer
Other Versions
Version B9
OTP Pull−Up Current Source
Autorecovery Timer
ms
LIGHT/NO LOAD MANAGEMENT
Minimum Frequency Clamp
Dead−Time Added During Frequency
Foldback
VFB = 400 mV
Quiet−Skip Timer
Skip Threshold
VFB decreasing
Vskip
350
400
450
mV
Skip Hysteresis
VFB increasing
Vskip(HYS)
20
50
70
mV
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NCP1340
Table 5. ELECTRICAL CHARACTERISTICS: (VCC = 12 V, VHV = 120 V, VFault = open, VFB = 2.4 V, VCS = 0 V, VZCD = 0 V, VFMAX
= 0 V, CVCC = 100 nF , CDRV = 100 pF, for typical values TJ = 25°C, for min/max values, TJ is – 40°C to 125°C, unless otherwise noted)
Characteristics
Conditions
Symbol
Min
Typ
Max
Unit
Thermal Shutdown
Temperature increasing
TSHDN
–
140
–
°C
Thermal Shutdown Hysteresis
Temperature decreasing
TSHDN(HYS)
–
40
–
°C
THERMAL PROTECTION
3. NTC with R110 = 8.8 kW
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9
NCP1340
INTRODUCTION
The NCP1340 implements a quasi−resonant flyback
converter utilizing current−mode architecture where the
switch−off event is dictated by the peak current. This IC is
an ideal candidate where low parts count and cost
effectiveness are the key parameters, particularly in ac−dc
adapters, open−frame power supplies, etc. The NCP1340
incorporates all the necessary components normally needed
in modern power supply designs, bringing several
enhancements such as non−dissipative overpower
protection (OPP), brownout protection, and frequency
reduction management for optimized efficiency over the
entire power range. Accounting for the needs of extremely
low standby power requirements, the controller features
minimized current consumption and includes an automatic
X2 capacitor discharge circuit that eliminates the need to
install power−consuming resistors across the X2 input
capacitors.
• High−Voltage Start−Up Circuit: Low standby power
consumption cannot be obtained with the classic
resistive start−up circuit. The NCP1340 incorporates a
high−voltage current source to provide the necessary
current during start−up and then turns off during normal
operation.
• Internal Brownout Protection: The ac input voltage is
sensed via the high−voltage pin. When this voltage is
too low, the NCP1340 stops switching. No restart
attempt is made until the ac input voltage is back within
its normal range.
• X2−Capacitor Discharge Circuitry: Per the
IEC60950 standard, the time constant of the X2 input
capacitors and their associated discharge resistors must
be less than 1 s in order to avoid electrical shock when
the user unplugs the power supply and inadvertently
touches the ac input cord terminals. By providing an
automatic means to discharge the X2 capacitors, the
NCP1340 eliminates the need to install X2 discharge
resistors, thus reducing power consumption.
• Quasi−Resonant, Current−Mode Operation:
Quasi−Resonant (QR) mode is a highly efficient mode
of operation where the MOSFET turn−on is
synchronized with the point where its drain−source
voltage is at the minimum (valley). A drawback of this
mode of operation is that the operating frequency is
inversely proportional to the system load. The
NCP1340 incorporates a valley lockout (VLO) and
frequency foldback technique to eliminate this
drawback, thus maximizing the efficiency over the
entire power range.
• Valley Lockout: In order to limit the maximum
frequency while remaining in QR mode, one would
traditionally use a frequency clamp. Unfortunately, this
can cause the controller to jump back and forth between
two different valleys, which is often undesirable. The
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NCP1340 patented VLO circuitry solves this issue by
determining the operating valley based on the system
load, and locking out other valleys unless a significant
change in load occurs.
Frequency Foldback: As the load continues to
decrease, it becomes beneficial to reduce the switching
frequency. When the load is light enough, the NCP1340
enters frequency foldback mode. During this mode, the
peak current is frozen and dead−time is added to the
switching cycle, thus reducing the frequency and
switching operation to discontinuous conduction mode
(DCM). Dead−time continues to be added until skip
mode is reached, or the switching frequency reaches its
minimum level of 25 kHz.
Skip Mode: To further improve light or no−load power
consumption while avoiding audible noise, the
NCP1340 enters skip mode when the operating
frequency reaches its minimum value. foldback isavoid
acoustic noise, the circuit prevents the switching
frequency from decaying below 25 kHz. This allows
regulation via burst of pulses at 25 kHz or greater
instead of operating in the audible range.
Quiet−Skip: To further reduce acoustic noise, the
NCP1340 incorporates a novel circuit to prevent the
skip mode burst period from entering the audible range
as well.
Internal OPP: In order to limit power delivery at high
line, a scaled version of the negative voltage present on
the auxiliary winding during the on−time is routed to
the ZCD/OPP pin. This provides the designer with a
simple and non−dissipative means to reduce the
maximum power capability as the bulk voltage
increases.
Frequency Jittering: In order to reduce the EMI
signature, a low frequency triangular voltage waveform
is added to the iniput of the PWM comparator. This
helps by spreading out the energy peaks during noise
analysis.
Internal Soft−Start: The NCP1340 includes a 4 ms
soft−start to prevent the main power switch from being
overly stressed during start−up. Soft−start is activated
each time a new startup sequence occurs or during
auto−recovery mode.
Dedicated Fault Input: The NCP1340 includes a
dedicated fault input. It can be used to sense an
overvoltage condition and latch off the controller by
pulling the pin above the overvoltage protection (OVP)
threshold. The controller is also disabled if the Fault pin
is pulled below the overtemperature protection (OTP)
threshold. The OTP threshold is configured for use with
a NTC thermistor.
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10
NCP1340
• Overload/Short−Circuit Protection: The NCP1340
•
HIGH VOLTAGE START−UP
The NCP1340 contains a multi−functional high voltage
(HV) pin. While the primary purpose of this pin is to reduce
standby power while maintaining a fast start−up time, it also
incorporates brownout detection and line removal detection.
The HV pin must be connected directly to the ac line in
order for the X2 discharge circuit to function correctly. Line
and neutral should be diode “ORed” before connecting to the
HV pin as shown in Figure 4. The diodes prevent the pin
voltage from going below ground. A resistor in series with
the pin should be used to protect the pin during EMC or surge
testing. A low value resistor should be used (
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