NCP12510 D

NCP12510
Product Preview
Current-Mode PWM
Controller for Off-line
Power Supplies
The NCP12510 is a highly integrated PWM controller capable of
delivering a rugged and high performance offline power supply in a
tiny TSOP−6 package. With a voltage supply range up to 35 V, the
controller hosts a jittered 65−kHz or 100−kHz switching circuitry
operated in peak current mode control. When the power on the
secondary side starts decreasing, the controller automatically folds
back its switching frequency down to a minimum level of 26 kHz. As
the power further goes down, the part enters skip cycle while limiting
the peak current.
Over Power Protection (OPP) is a difficult exercise especially when
no−load standby requirements drive the converter specifications. The
ON Semiconductor proprietary integrated OPP allows harness the
maximum delivered power without affecting the standby performance
simply via two external resistors. An Over Voltage Protection (OVP)
input is also combined on the same pin and protects the whole circuitry
in case of optocoupler destruction or adverse open loop operation.
Finally, a timer−based short−circuit protection offers the best
protection scheme, allowing precisely select the protection trip point
without caring of a loose coupling between the auxiliary and the power
windings.
NCP12510 is improved and pin compatible controller based on very
popular flyback controller NCP1250.
Features
• Fixed−Frequency 65 kHz or 100 kHz Current−Mode Control
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MARKING
DIAGRAM
TSOP−6
(SOT23−6)
SN SUFFIX
CASE 318G
STYLE 13
1
5Dx
x
A
Y
W
G
5DxAYWG
G
1
= Specific Device Code
= A, 2, J, or K
= Assembly Location
= Year
= Work Week
= Pb−Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
GND
1
6
DRV
FB
2
5
VCC
OPP/Latch
3
4
CS
Operation
(Top View)
Frequency Foldback Down to 26 kHz and Skip−Cycle in Light Load
Conditions
ORDERING INFORMATION
Frequency Jittering in Normal and Frequency Foldback Modes
See detailed ordering, marking and shipping information on
Internal and Adjustable Over Power Protection (OPP) Circuit
page 2 of this data sheet.
Auto−Recovery Over Voltage Protection (OVP) on the VCC Pin
Internal and Adjustable Slope Compensation
Internal Fixed 4 ms Soft−Start
Auto−Recovery or Latched Short−Circuit Protection
• EPS 2.0 Compliant
Pre−Short Ready for Latched OCP Version
• This is a Pb−Free Device
OVP/OTP Latch Input for Improved Robustness
Typical Applications
+300 mA/ −500 mA Source/Sink Drive Capability
• Ac−dc Converters for TVs, Set−top Boxes and DVD
Improved Consumption
Players
Improved Reset Time in Latch State
• Offline Adapters for Notebooks and Netbooks
High Robustness and High ESD Capabilities
This document contains information on a product under development. ON Semiconductor
reserves the right to change or discontinue this product without notice.
© Semiconductor Components Industries, LLC, 2016
May, 2016 − Rev. P0
1
Publication Order Number:
NCP12510/D
NCP12510
Figure 1. Typical Application Example
Table 1. PIN DESCRIPTION
Pin No
Pin Name
Function
Pin Description
1
GND
−
2
FB
Feedback pin
3
OPP/Latch
Adjust the Over Power
Protection Latches off the part
4
CS
Current sense + slope
compensation
5
VCC
Supplies the controller −
protects the IC
6
DRV
Driver output
The controller ground.
Hooking an optocoupler collector to this pin will allow regulation.
A resistive divider from the auxiliary winding to this pin sets the OPP
compensation level during the on−time. When the voltage exceeds a certain
level at turn off, the part is fully latched off.
This pin monitors the primary peak current but also offers a means to
introduce slope compensation.
This pin is connected to an external auxiliary voltage. When the VCC exceeds a
certain level, the part enters an auto−recovery hiccup.
The driver output to an external MOSFET gate.
Table 2. ORDERING INFORMATION
Package
Marking
OCP Protection
OVP/OTP
Protection
Switching
Frequency
NCP12510ASN65T1G
5DA
Latched
Latched
65 kHz
NCP12510BSN65T1G
5D2
Auto−recovery
Latched
65 kHz
NCP12510ASN100T1G
5DJ
Latched
Latched
100 kHz
NCP12510BSN100T1G
5DK
Auto−recovery
Latched
100 kHz
Controller (Note 1)
Package
Shipping†
TSOP−6
(Pb−Free)
3000 /
Tape & Reel
†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.
1. Other options available upon customer request.
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2
NCP12510
OPP/
Latch
VOPP
VCC(OVP)
DRV stop
Latch / Autorecovery mode
RST
+
tlatch(del)
VCC(min)
Latch / Auto-revery
management
OVP/OTP
Latch
Note: depend on IC
option
OCP Fault
Up Counter
to 4
Pre-short
_
+
Vlatch
OVP/OTP
Latch
Latch / Autorecovery mode
IC start
IC stop
VCC and logic
management
DRV pulse
tlatch(blank)
IC reset
Internal
supply
Armed
flag
VCC(on)
VCC(OVP)
VCC
+
tOVP(del)
_
st
1 DRV pulse
during IC start
S
Q
Pre-short
R
Q
(for OCP&UVLO
latched option )
IC in regulation
[email protected]
+
VOVP
VCC(min)
Clamp
DRV pulse
DRV
pulse
Jittering
65 / 100 kHz
Oscillator
Frequency
foldback
Rramp
Dmax
S
Q
R
Q
DRV
IC stop
DRV pulse
DRV stop
_
+
+
Vskip
VFB(open)
IC in regulation
Req
Kratio
FB
Up counter
to 8
_
+
RST
peak current
freeze
Error
flag
Soft-start
LEB
R
Q
S
Q
RST
+
VOPP
+
Vlimit + VOPP
Fault timer
OCP
Fault
_
CS
+
Vlimit
GND
Figure 2. Internal Circuit Architecture
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NCP12510
Table 3. MAXIMUM RATINGS TABLE
Symbol
Rating
VCC
Power Supply voltage, VCC pin, continuous voltage
VDRV(tran)
Maximum DRV pin voltage when DRV in H state, transient voltage (Note 1)
VCS, VFB, VOPP
Unit
−0.3 to 35
V
−0.3 to VCC + 0.3
V
−0.3 to 5.5
V
VOPP(tran)
Maximum negative transient voltage on OPP pin (Note 2)
−1
V
Isource,max
Maximum sourced current, pulsed width < 800 ns
0.6
A
Isink,max
Maximum voltage on low power pins CS, FB and OPP (Note 2)
Value
Maximum sinked current, pulse width < 800 ns
1.0
A
IOPP
Maximum injected negative current into the OPP pin (pin 3)
−2
mA
RθJ−A
Thermal Resistance Junction−to−Air
360
°C/W
TJ,max
Maximum Junction Temperature
150
°C
−60 to +150
°C
4
kV
750
V
Storage Temperature Range
HBM
Human Body Model ESD Capability per JEDEC JESD22−A114F (All pins)
CDM
Charged−Device Model ESD Capability per JEDEC JESD22−C101E
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 transient voltage is a voltage spike injected to DRV pin being in high state. Maximum transient duration is 100 ns.
2. See the Figure 3 for detailed specification of transient voltage.
3. This device contains latch−up protection and exceeds 100 mA per JEDEC Standard JESD78.
on-time
500 ns
t
0V
VCS
VFB
VOPP
VOPP (t)
7.5 V – Max transient
voltage
cycle-by-cycle
VOPP, max
5.5 V – Max DC
voltage
VOPP,max = -0.75 V, Tj = -25 °C
VOPP,max = -0.65 V, Tj = 25 °C
VOPP,max = -0.3 V, Tj = 125 °C – Worst case
VOPP
-1 V
SOA
VOPP must stay between 0V and –0.3 V for
a linear OPP operation
500 ns
Max current during
overshoot can 't
exceed 3 mA
0V
t
Figure 3. Negative Pulse for OPP Pin during On−time and Positive Pulse for All Low Power Pins
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NCP12510
Table 4. ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted)
Rating
Symbol
Pin
Min
Typ
Max
Unit
SUPPLY SECTION
VCC(on)
VCC increasing level at which driving pulses are authorized
5
16
18
20
V
VCC(min)
VCC decreasing level at which driving pulses are stopped
5
8.3
8.9
9.5
V
VCC(hyst)
Hysteresis VCC(on) – VCC(min)
5
7.7
−
−
V
VCC(reset)
Latched state reset voltage
5
−
8.6
−
V
VCC(reset_
Defined hysteresis between minimum and reset voltage VCC(min) –
VCC(reset)
5
0.15
0.30
0.45
V
Defined hysteresis for hiccupping between two voltage levels in latch mode
5
−
0.55
−
V
ICC1
Start−up current (VCC(on) – 100 mV)
5
−
6
10
mA
ICC2
Internal IC consumption with VFB = 3.2 V, fSW = 65 kHz and CL = 0 nF
Internal IC consumption with VFB = 3.2 V, fSW = 100 kHz and CL = 0 nF
5
−
1.0
1.1
1.4
1.5
mA
ICC3
Internal IC consumption with VFB = 3.2 V, fSW = 65 kHz and CL = 1 nF
Internal IC consumption with VFB = 3.2 V, fSW = 100 kHz and CL = 1 nF
5
−
1.7
2.3
2.7
3.0
mA
Internal consumption in skip mode – non switching, VFB = 0 V
5
−
300
−
mA
Internal consumption in fault mode – during going−down VCC cycle,
VFB = 4 V
5
−
340
−
mA
Internal IC consumption in skip mode for 65 kHz version (VCC = 14 V,
driving a typical 7−A/600−V MOSFET, includes opto current) – (Note 5)
5
−
420
−
mA
hyst)
VCC(latch_hyst)
ICC(no−load)
ICC(fault)
ICC(standby)
DRIVE OUTPUT
tr
Output voltage rise−time @ CL = 1 nF, 10−90% of output signal
6
−
40
−
ns
tf
Output voltage fall−time @ CL = 1 nF, 10−90% of output signal
6
−
30
−
ns
ROH
Source resistance, VCC = 12 V, IDRV = 100 mA
6
−
28
−
W
ROL
Sink resistance, VCC = 12 V, IDRV = 100 mA
6
−
7
−
W
Peak source current, VGS = 0 V (Note 4)
6
−
300
−
mA
Peak sink current, VGS = 12 V (Note 4)
6
−
500
−
mA
VDRV(low)
DRV pin level at VCC = VCC(min) + 100 mV with a 33 kW resistor to GND
6
8
−
−
V
VDRV(high)
DRV pin level at VCC = VOVP – 100 mV (DRV unloaded)
6
10
12
14
V
Maximum internal current set point – TJ = 25°C – pin 3 grounded
Maximum internal current set point – TJ = −40°C to 125°C – pin 3 grounded
4
0.744
0.720
0.8
0.8
0.856
0.880
V
Internal voltage setpoint for frequency foldback trip point – 59% of Vlimit
4
−
475
−
mV
Isource
Isink
CURRENT COMPARATOR
Vlimit
VCS(fold)
VCS(freeze)
Internal peak current setpoint freeze (≈31% of Vlimit)
4
−
250
−
mV
tDEL
Propagation delay from CS pin to DRV output
4
−
50
80
ns
tLEB
Leading Edge Blanking Duration
4
−
300
−
ns
tSS
Internal soft−start duration activated upon startup or auto−recovery
4
−
4
−
ms
IOPPs
Set point decrease for pin 3 grounded
3
−
0
−
%
IOPPo
Set point decrease for pin 3 biased to −250 mV (Note 4)
3
−
31.3
−
%
IOOPv
Voltage set point for pin 3 biased to −250 mV, TJ = 25°C
Voltage set point for pin 3 biased to −250 mV, TJ = −40° to 125°C
3
0.51
0.50
0.55
0.55
0.60
0.62
V
Oscillation frequency (65 kHz version)
Oscillation frequency (100 kHz version)
−
61
92
65
100
71
108
kHz
Maximum duty−ratio
−
76
80
84
%
INTERNAL OSCILLATOR
fOSC(nom)
Dmax
4. Guaranteed by design.
5. Application parameter for information only.
6. 1−MW resistor is connected from pin 4 to the ground for the measurement.
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NCP12510
Table 4. ELECTRICAL CHARACTERISTICS
(For typical values TJ = 25°C, for min/max values TJ = −40°C to +125°C, VCC = 12 V unless otherwise noted)
Symbol
Rating
Pin
Min
Typ
Max
Unit
INTERNAL OSCILLATOR
fjitter
Frequency jittering in percentage of fOSC – jitter is kept even in foldback
mode
−
−
±5
−
%
fswing
Swing frequency
−
−
240
−
Hz
FEEDBACK SECTION
Req
Internal equivalent feedback resistance
2
−
29
−
kW
Kratio
FB pin to current set point division ratio
−
−
4
−
−
Feedback voltage below which the peak current is frozen
2
−
1.2
−
V
VFB(limit)
Feedback voltage corresponding with maximum internal current set point
2
−
3.2
−
V
VFB(open)
Internal pull−up voltage on FB pin
2
−
4
−
V
Frequency foldback level on the FB pin – ≈59% of maximum peak current
−
−
1.9
−
V
Minimum operating frequency
−
22
26
30
kHz
End of frequency foldback feedback level, fsw = ftrans
−
−
1.5
−
V
Skip−cycle level voltage on the feedback pin
−
−
0.8
−
V
Hysteresis on the skip comparator (Note 4)
−
−
50
−
mV
VFB(freeze)
FREQUENCY FOLDBACK
Vfold(start)
ftrans
Vfold(end)
Vskip
Vskip(hyst)
INTERNAL SLOPE COMPENSATION
Vramp
Internal ramp level @ 25°C (Note 6)
4
−
2.5
−
V
Rramp
Internal ramp resistance to CS pin
4
−
20
−
kW
PROTECTIONS
Vlatch
Latching level input on OPP/Latch pin
3
2.85
3.0
3.15
V
tlatch(blank)
Blanking time after Drive output turn off (Note 4)
3
−
1
−
ms
tlatch(count)
Number of clock cycles before latch is confirmed (Note 4)
3
−
4
−
OVP/OTP delay time constant before latch is confirmed (Note 4)
3
−
600
−
ns
Over voltage protection on the VCC pin
5
24.0
25.5
27.0
V
Delay time constant before OVP on VCC is confirmed (Note 4)
5
−
20
−
ms
Internal fault timer duration
−
100
115
130
ms
tlatch(del)
VOVP
tOVP(del)
tfault
4. Guaranteed by design.
5. Application parameter for information only.
6. 1−MW resistor is connected from pin 4 to the ground for the measurement.
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NCP12510
TYPICAL CHARACTERISTICS
20.0
9.0
19.5
8.9
8.8
8.7
VCC(reset) (V)
VCC(on) (V)
19.0
18.5
18.0
17.5
8.4
8.2
16.5
−25
0
25
50
75
100
8.1
8.0
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 4.
Figure 5.
9.4
500
9.3
450
VCC(reset_hyst) (mV)
9.2
9.1
VCC(min) (V)
8.5
8.3
17.0
16.0
−50
8.6
9.0
8.9
8.8
8.7
100
125
100
125
100
125
400
350
300
250
200
8.6
8.5
8.4
−50
150
−25
0
25
50
75
100
100
−50
125
25
50
75
TEMPERATURE (°C)
Figure 6.
Figure 7.
900
9.5
800
VCC(latch_hyst) (V)
9.4
VCC(hyst) (V)
0
TEMPERATURE (°C)
9.6
9.3
9.2
9.1
9.0
700
600
500
400
300
8.9
8.8
−50
−25
−25
0
25
50
75
100
200
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 8.
Figure 9.
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NCP12510
TYPICAL CHARACTERISTICS
500
9
450
8
400
ICC(no−load) (mA)
10
ICC1 (mA)
7
6
5
4
350
300
250
3
200
2
150
1
−50
−25
0
25
50
75
100
100
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 10.
Figure 11.
100
125
100
125
500
1.6
65 kHz
1.5
450
1.4
400
ICC(fault) (mA)
ICC2 (mA)
1.3
1.2
1.1
1.0
0.9
350
300
250
200
0.8
0.7
0.6
−50
150
−25
0
25
50
75
100
100
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 12.
Figure 13.
2.4
4.0
65 kHz
2.3
3.5
2.2
3.0
2.0
ICC (mA)
ICC3 (mA)
2.1
1.9
1.8
1.7
2.5
2.0
1.5
1.0
1.6
1.5
1.4
−50
0.5
VIN = 120 Vac
0
−25
0
25
50
75
100
125
0
0.5
1.0
1.5
2.0
2.5
TEMPERATURE (°C)
ADAPTER OUTPUT CURRENT (A)
Figure 14.
Figure 15.
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3.0
3.5
NCP12510
TYPICAL CHARACTERISTICS
65
50
60
45
55
40
45
ROH (W)
tr (ns)
50
40
35
35
30
25
30
20
25
20
15
−50
15
−25
0
25
50
75
100
10
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 16.
Figure 17.
100
125
100
125
100
125
16
55
50
14
45
VDRV(low) (W)
tf (ns)
40
35
30
25
20
15
10
5
−50
10
8
6
−25
0
25
50
75
100
4
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 18.
Figure 19.
22
40
20
35
18
VDRV(high) (W)
30
ROL (W)
12
25
20
15
16
14
12
10
8
10
6
5
0
−50
−25
0
25
50
75
100
4
2
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 20.
Figure 21.
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NCP12510
TYPICAL CHARACTERISTICS
1.00
55
0.95
50
45
tDEL (ns)
Vlimit (V)
0.90
0.85
0.80
25
0.70
−25
0
25
50
75
100
15
−50
125
280
tLEB (ns)
550
500
450
350
200
25
50
75
100
180
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 24.
Figure 25.
350
6.0
325
5.5
300
5.0
275
4.5
250
3.5
200
3.0
175
2.5
50
75
100
2.0
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 26.
Figure 27.
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10
125
100
125
100
125
4.0
225
25
100
240
220
0
75
260
400
−25
50
Figure 23.
300
150
−50
25
Figure 22.
600
0
0
TEMPERATURE (°C)
320
−25
−25
TEMPERATURE (°C)
tSS (ms)
VCS(fold) (mV)
20
650
300
−50
VCS(freeze) (mV)
35
30
0.75
0.65
−50
40
NCP12510
TYPICAL CHARACTERISTICS
125
0.9
120
0.8
115
fOSC(nom) (kHz)
1.0
IOPPv (V)
0.7
0.6
0.5
0.4
105
100
95
90
85
0.2
80
75
−50
−25
0
25
50
75
100
125
0
25
50
75
TEMPERATURE (°C)
Figure 28.
Figure 29.
50
95
45
90
100
125
100
125
100
125
Dmax (%)
85
35
30
80
75
25
70
20
15
−50
−25
TEMPERATURE (°C)
40
IOPPo (%)
110
0.3
0.1
−50
100 kHz
−25
0
25
50
75
100
65
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 30.
Figure 31.
295
90
65 kHz
85
285
275
75
fswing (Hz)
fOSC(nom) (kHz)
80
70
65
60
265
255
245
55
235
50
45
−50
−25
0
25
50
75
100
225
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 32.
Figure 33.
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NCP12510
TYPICAL CHARACTERISTICS
2.8
45
2.6
40
2.4
Vfold(start) (V)
Req (kW)
35
30
25
2.2
2.0
1.8
1.6
20
15
−50
1.4
−25
0
25
50
75
100
1.2
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 34.
Figure 35.
100
125
100
125
100
125
2.4
7.5
2.2
6.5
2.0
Vfold(end) (V)
Kratio (−)
5.5
4.5
3.5
1.8
1.6
1.4
1.2
2.5
1.5
−50
1.0
−25
0
25
50
75
100
0.8
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 36.
Figure 37.
1.4
2.0
1.8
1.2
1.0
1.4
Vskip (V)
VFB(freeze) (V)
1.6
1.2
1.0
0.8
0.6
0.8
0.6
0.4
0.4
0.2
−50
−25
0
25
50
75
100
0.2
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 38.
Figure 39.
www.onsemi.com
12
NCP12510
TYPICAL CHARACTERISTICS
27.5
70
65
27.0
26.5
55
VOVP (V)
Vskip(hyst) (mV)
60
50
45
26.0
25.5
40
25.0
35
30
−50
−25
0
25
50
75
100
24.5
−50
125
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 40.
Figure 41.
34
130
32
125
30
100
125
100
125
tfault (ms)
120
28
26
115
110
24
105
22
20
−50
−25
0
25
50
75
100
100
−50
125
−25
0
25
50
75
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 42.
Figure 43.
4.5
4.0
3.5
Vlatch (V)
ftrans (kHz)
−25
3.0
2.5
2.0
1.5
−50
−25
0
25
50
75
TEMPERATURE (°C)
Figure 44.
www.onsemi.com
13
100
125
NCP12510
APPLICATION INFORMATION
Introduction
NCP12510 implements a standard current mode
architecture where the switch−off event is dictated by the
peak current set point. This component represents the ideal
candidate where low part−count and cost effectiveness are
the key parameters, particularly in low−cost ac−dc adapters,
open−frame power supplies etc. Updated controller, the
NCP12510 packs all the necessary components normally
needed in today modern power supply designs, bringing
several enhancements such as a non−dissipative OPP,
OVP/OTP implementation, short−circuit protection with
pre−short ready for latched version and improved
consumption, robustness and ESD capabilities.
• Current−mode operation with internal slope
compensation: implementing peak current mode
control at a 65 or 100 kHz switching frequency, the
NCP12510 offers an internal slope compensation signal
that can easily by summed up to the sensed current. Sub
harmonic oscillations can thus be fought via the
inclusion of a simple resistor in series with the
current−sense information.
• Internal OPP: by routing a portion of the negative
voltage present during the on−time on the auxiliary
winding to the dedicated OPP pin (pin 3), the user has a
simple and non−dissipative means to alter the
maximum peak current set point as the bulk voltage
increases. If the pin is grounded, no OPP compensation
occurs. If the pin receives a negative voltage, then a
peak current is reduced down.
• Low startup and standby current: reaching a low
no−load standby power always represents a difficult
exercise when the controller draws a significant amount
of current during startup. The NCP12510 brings
improved consumption to easing the design of low
standby power adapters.
• EMI jittering: an internal low−frequency modulation
signal varies the pace at which the oscillator frequency
is modulated. This helps spreading out energy in
conducted noise analysis. To improve the EMI
signature at low power levels, the jittering is kept in
frequency foldback mode (light load conditions).
• Frequency foldback capability: a continuous flow of
pulses is not compatible with no−load/light−load
standby power requirements. To excel in this domain,
the controller observes the feedback pin and when it
reaches a level of Vfold(start) , it starts reduce switching
frequency. When the feedback level reaches Vfold(end) ,
the frequency hits its lower stop at ftrans . When the
feedback pin goes further down and reaches VFB(freeze) ,
the peak current setpoint is internally frozen. Below this
point, if power continues to drop, the controller enters
•
•
•
•
classical skip−cycle mode, as both frequency and peak
current are frozen.
Internal soft−start: a soft−start precludes the main
power switch from being stressed upon start−up. The
soft−start duration is internally fixed for time tSS and it
is activated during new startup sequence or during
recovering after auto−recovery double hiccup.
Latch input: the controller includes a latch input (pin
3) that can be used to sense an over voltage or an over
temperature event on the adapter. If this pin is brought
higher than the internal reference voltage Vlatch for four
consecutive cycles, then the circuit is latched off – VCC
hiccups from VCC(min) voltage level with hysteresis
VCC(latch_hyst) = 550 mV typically, until a reset occurs.
The latch reset occurs when the user disconnects the
adapter from the mains and lets the VCC falls below the
VCC(reset) level. For the C version, despite an OVP/OTP
detection, the circuit autorecovers and never latches.
Auto−recovery OVP on VCC: an OVP protects the
circuit against VCC runaways. If the fault is present at
least for time tOVP(del) then the OVP is validated and
the controller enters double hiccup mode. When the
VCC returns to a nominal level, the controller resumes
operation.
Short−circuit protection: short−circuit and especially
overload protections are difficult to implement when a
strong leakage inductance between auxiliary and power
windings affects the transformer (the aux winding level
does not properly collapse in presence of an output
short). In this controller, every time the internal
maximum peak current limit Vlimit is activated (or less
when OPP is used), an error flag is asserted and a time
period starts thanks to an internal timer. When the timer
has elapsed while a fault is still present, the controller is
latched or enters an auto−recovery mode, depending on
the selected OCP option.
Please note that with the latched OCP&UVLO option,
the part becomes sensitive to the first UVLO event
during the start−up sequence. Any other UVLO events
are ignored afterwards – auto−recovery operation. With
the first drive pulse is generated armed flag. Armed flag
is reset after the first successful start−up sequence (the
controller gets into regulation). This is to pass the
pre−short test at power up:
1. if the internal armed flag is active and an UVLO
event is sensed, the part is immediately latched.
2. if an UVLO signal is detected but the armed flag is
not asserted, double−hiccup auto−recovery occurs.
3. if the controller gets into regulation, the armed flag
is reset. Then UVLO event is sensed, the part is in
auto−recovery operation.
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14
NCP12510
Start−up Sequence
the start−up time. To further reduce the standby power, the
start−up current of the controller is extremely low, below
10 mA. The start−up resistor can therefore be connected to
the bulk capacitor or directly to the mains input voltage to
further reduce the power dissipation.
The NCP12510 start−up voltage is made purposely high
to permit large energy storage in a small VCC capacitor
value. This helps operate with a small start−up current
which, together with a small VCC capacitor, will not hamper
Rstart-up
+
Input
mains
Cbulk
VCC
+
+
aux.
winding
CVCC
Figure 45. The startup resistor can be connected to the input mains for further power dissipation reduction.
To make sure this current is always greater than 26 mA,
then, the minimum value for Rstart−up can be extracted:
The first step starts with the calculation of the needed
VCC capacitor which will supply the controller which it
operates until the auxiliary winding takes it over. Experience
shows that this time t1 can be between 5 and 20 ms. If we
consider we need at least an energy reservoir for a t1 time of
10 ms, the VCC capacitor must be larger than:
C VCC w
I CC @ t 1
V CC(on) * V CC(min)
w
1.7 m @ 10 m
18 * 8.9
R start*up v
V CC(on) @ C VCC
t start*up
w
18 @ 2.2 m
2.5
w 16 mA
(eq. 1)
PR
(eq. 2)
If we account for the 10 mA (maximum) that will flow to
the controller, then the total charging current delivered by
the start−up resistor must be 26 mA. If we connect the
start−up network to the mains (half−wave connection then),
we know that the average current flowing into this start−up
resistor will be the smallest when VCC reaches the VCC(on)
of the controller:
I CVCC,min +
V ac,rmsǸ2
* V CC(on)
p
R start*up
I CVCC(min)
v
85Ǹ2
p * 18
26 m
v 779 kW
(eq. 4)
This calculation is purely theoretical, considering a
constant charging current. In reality, the take over time can
be shorter (or longer!) and it can lead to a reduction of the
VCC capacitor. Thus, a decrease in charging current and an
increase of the start−up resistor can be experimentally
tested, for the benefit of standby power. Laboratory
experiments on the prototype are thus mandatory to fine tune
the converter. If we chose the 750 kW resistor as suggested
by Equation 4, the dissipated power at high line amounts to:
w 1.9 mF
Let us select a 2.2 mF capacitor at first and experiments in
the laboratory will let us know if we were too optimistic for
the time t1 . The VCC capacitor being known, we can now
evaluate the charging current we need to bring the VCC
voltage from 0 V to the VCC(on) of the IC. This current has
to be selected to ensure a start−up at the lowest mains
(85 Vrms) to be less than 3 s (2.5 s for design margin):
I charge w
V ac,rmsǸ2
* V CC(on)
p
start*up,max
[
V ac,peak 2
4 @ R start*up
[
ǒ230 @ Ǹ2Ǔ
4 @ 750 k
2
[ 35 mW
(eq. 5)
Now that the first VCC capacitor has been selected, we
must ensure that the self−supply does not disappear when in
no−load conditions. In this mode, the skip−cycle can be so
deep that refreshing pulses are likely to be widely spaced,
inducing a large ripple on the VCC capacitor. If this ripple
is too large, chances exist to touch the VCC(min) and reset the
controller into a new start−up sequence. A solution is to
grow this capacitor but it will obviously be detrimental to the
start−up time. The option offered in Figure 45 elegantly
solves this potential issue by adding an extra capacitor on the
auxiliary winding. However, this component is separated
(eq. 3)
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15
NCP12510
have amplitude depending on the input voltage. The idea
implemented in this chip is to sum a portion of this negative
swing with the internal voltage reference Vlimit = 0.8 V. For
instance, if the voltage swings down to −150 mV during the
on−time, then the internal peak current set point will be fixed
to the value 0.8 V – 0.150 V = 650 mV. The adopted principle
appears in Figure 47 and shows how the final peak current
set point is constructed.
Let’s assume we need to reduce the peak current from
2.5 A at low line, to 2 A at high line. This corresponds to a
20% reduction or a set point voltage of 640 mV. To reach this
level, then the negative voltage developed on the OPP pin
must reach:
from the VCC pin via a simple diode. You therefore have the
ability to grow this capacitor as you need to ensure the
self−supply of the controller without affecting the start−up
time and standby power.
Internal Over Power Protection
There are several known ways to implement Over Power
Protection (OPP), all suffering from particular problems.
These problems range from the added consumption burden
on the converter or the skip−cycle disturbance brought by
the current−sense offset. A way to reduce the power
capability at high line is to capitalize on the negative voltage
swing present on the auxiliary diode anode. During the
turn−on time, this point dips to –N2 Vbulk , where N2 being the
turns ratio between the primary winding and the auxiliary
winding. The negative plateau observed on Figure 46 will
V OPP + 0.8 @ V limit * V limit + 0.64 * 0.8 + −160 mV
(eq. 6)
1 v(24)
40.0
off−time
N1(Vout+Vf)
20.0
Plot1
v(24) in volts
1
0
−N2Vbulk
−20.0
on−time
−40.0
464u
472u
480u
time in seconds
488u
496u
Figure 46. The signal obtained on the auxiliary winding swings negative during the on−time.
www.onsemi.com
16
NCP12510
ROPPU
This point will be
adjusted to reduce
the „ref“ at hi line to
the desired level
swings to:
N1Vout during toff
-N2Vin during ton
VCC
+
aux.
winding
ref = 0.8V + VOPP
(VOPP is negative)
IOPP
driver reset
K1
ref
SUM
_
OPP
K2
+
+
Vlimit = 0.8 V ± 7%
ROPPL
CS
Rsense
Figure 47. The OPP circuitry affects the maximum peak current set point by summing a negative voltage to the
internal voltage reference.
Let us assume that we have the following converter
characteristics:
Vout = 19 V
Vin = 85 to 265 Vrms
N1 = Np:Ns = 1:0.25
N2 = Np:Naux = 1:0.18
Given the turns ratio between the primary and the auxiliary
windings, the on−time voltage at high line (265 Vrms) on the
auxiliary winding swings down to:
V aux + −N 2 @ V in,max + −0.18 @ 375 + −67.5 V
Div +
V OPP
+ −0.16 [ 2.4 m
−67.5
V aux
(eq. 8)
If we arbitrarily fix the pull−down resistor ROPPL to 1 kW,
then the upper resistor can be obtained by:
R OPPU +
V aux * V OPP
VOPP
ROPPL
+ −67.5 ) 0.16 [ 422 kW (eq. 9)
−0.16
1k
If we now plot the peak current set point obtained by
implementing the recommended resistor values, we obtain
the following curve, as shown in Figure 48.
(eq. 7)
To obtain a level as imposed by Equation 7, we need to
install a divider featuring the following ratio:
Peak current
setpoint
100%
80%
Vbulk
375 V
Figure 48. The peak current regularly reduces down to 80% at 375 Vdc.
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17
NCP12510
Frequency Foldback
The OPP pin is surrounded by Zener diodes stacked to
protect the pin against ESD pulses. These diodes accept
some peak current in the avalanche mode and are designed
to sustain a certain amount of energy. On the other side,
negative injection into these diodes (or forward bias) can
cause substrate injection which can lead to an erratic circuit
behavior. To avoid this problem, the pin is internal clamped
slightly below –300 mV which means that if more current is
injected before reaching the ESD forward drop, then the
maximum peak reduction is kept to 40%. If the voltage
finally forward biases the internal zener diode, then care
must be taken to avoid injecting a current beyond –2 mA.
Given the value of ROPPU , there is no risk in the present
example.
Finally, please note that another comparator internally
fixes the maximum peak current set point to value Vlimit even
if the OPP pin is adversely biased above 0 V.
The reduction of no−load standby power associated with
the need for improving the efficiency, requires a change in
the traditional fixed−frequency type of operation. This
controller implements a switching frequency foldback when
the feedback voltage passes below a certain level, Vfold(start) .
At this point, the oscillator turns into a Voltage−Controlled
Oscillator (VCO) and reduces switching frequency down to
ftrans value, till to feedback voltage reaches the level
Vfold(end) . Below this level Vfold(end) , the frequency is fixed
and cannot go further down. The peak current setpoint is
following the feedback pin until its level reaches VFB(freeze) .
Below this value, the peak current setpoint is frozen to
VCS(freeze) value or ≈31% of the maximum Vlimit setpoint.
The only way to further reduce the transmitted power is to
enter skip cycle, which is set when the feedback voltage
reaches the level Vskip . Skip cycle offers the best noise−free
performance in no−load conditions. Figure 49 and depicts
the adopted scheme for the part.
Frequency
Peak current setpoint
fSW
VCS
max
Vlimit
fOSC(nom)
FB
VCS(fold)
ftrans
VCS(freeze)
VFB
min
Vskip VFB(freeze)
Vskip Vfold(end) Vfold(start) VFB(limit) VFB(open)
Vfold(start) VFB(limit)
VFB
Figure 49. By observing the voltage on the feedback pin, the controller reduces its switching frequency for an
improved performance at light load.
VFB [V]
Open loop
VFB(open )
Peak current
is clamped
VFB(limit)
Vfold(start)
Vfold(end)
Ipeak , max
fSW is fixed
to f OSC(nom)
Peak current
is chang ing
fOSC(nom)
fSW is changing
ftrans
Ipeak , min
VFB(freeze )
Vskip
Peak current
is frozen
Skip mode
t
Figure 50. Another look at the relationship between feedback and current setpoint while in frequency reduction
mode.
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18
NCP12510
Auto−Recovery Short−Circuit Protection
up again thanks to the resistive starting network. When VCC
reaches VCC(on) , the controller purposely ignores the re−start
and waits for another VCC cycle: this is the so−called double
hiccup auto−recovery mode. By lowering the duty ratio in
fault condition, it naturally reduces the average input power
and the rms current in the output cable. Illustration of such
principle appears in Figure 51. Please note that soft−start is
activated upon re−start attempt.
In case of output short−circuit or if the power supply
experiences a severe overloading situation, an internal error
flag is raised and starts a countdown fault timer. If the UVLO
has come or the flag is asserted longer than fault timer value
tfault (depends on chosen option), the driving pulses are
stopped and the VCC falls down as the auxiliary pulses are
missing. When it crosses VCC(min) , the controller
consumption is down to a few mA and the VCC slowly builds
VCC (t)
Short-circuit -> start timer ->
Error flag + UVLO -> auto-recovery
Overload -> start fault timer ->
timer elapsed -> auto-recovery
VCC(on)
VCC(min)
t
VDRV (t)
t
Error flag
Fault timer has
elapsed
Fault timer has
elapsed
t
VCS (t)
SS
Vlimit
t
Figure 51. An auto−recovery double hiccup mode is entered in case a faulty event longer than programmable
fault timer value is acknowledged by the controller.
Latched Short−Circuit Protection with Pre−Short
pre−short situation: upon start−up with first drive pulse, the
armed flag is raised until regulation is met. If during the time
the flag is raised an UVLO event is detected, the part latches
off immediately. When IC is latched, VCC enters hiccup
mode. In normal operation, if an UVLO event is detected for
any reason, the controller will naturally resume operations.
Details of this behavior are given in Figure 52.
UVLO latch is made available solely during the start−up
sequence. When the power supply starts−up, the armed flag
is asserted with the first drive pulse. If an UVLO event
occurs when the armed flag is asserted, the part immediately
latches off. If no UVLO occurs, once the output voltage has
reached regulation after 8 consecutive cycles, the internal
armed flag is released and the latch authorizing UVLO
detections is reset: any new UVLO events will simply be
ignored. In the latched option OCP&UVLO, the UVLO test
is available at the first power−up or when the part recovering
from double hiccup mode.
In some applications, the controller must be fully latched
in case of an output short circuit presence. In that case, you
would select a controller with an OCP latched option in the
Options table. When the error flag is asserted, meaning the
controller is asked to deliver its full peak current, the
controller latches off upon timer completion: all pulses are
immediately stopped and VCC hiccups between the two
voltage levels, given by a VCC(min) level and added
hysteresis VCC(latch_hyst) , until a reset occurs (VCC falls
down below VCC(reset) ). However, in presence of a small
VCC capacitor, it can very well be the case where the stored
energy does not give enough time to let the timer elapse
before VCC touches the UVLO. When this happens, the latch
is not acknowledged since the timer countdown has been
prematurely aborted. To avoid this problem, NCP12510
(with latched OCP&UVLO option) combines the armed
flag assertion together with the UVLO event to confirm a
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19
NCP12510
latched
new sequence
resumed
resumed
latched
VCC (t)
VCC(on)
VCC(latch_hyst)
VCC(min)
VCC(reset)
t
[email protected]
AND
armed flag
VDRV (t)
UVLO after regulation [email protected]
NO
AND
armed flag
armed flag
glitch
t
Armed
flag
1
1
0
t
VCS (t)
8 cycles
8 cycles
Vlimit
t
Figure 52. Full latch occurs in case the [email protected]−up or @recovering is detected while the armed flag is asserted
restart
latched
latched
VCC (t)
VCC(on)
The V CC hysteresis in latch mode
significantly improves the reset time .
VCC(latch_hyst)
VCC(min)
VCC(reset)
t
When the IC is latched, the user
have to unplugged and plugged
the adapter to the outlet
VDRV (t)
Armed
flag
Error flag
t
1
Fault timer has
elapsed
0
VCS (t)
[email protected]
AND
armed flag
Armed flag
t
Error flag
8 cycles
SS
Vlimit
t
Figure 53. Full latch occurs in case the fault timer has elapsed or [email protected]−up is detected with asserted
armed flag.
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20
NCP12510
Operation with Grounded Feedback Pin
When the VCC touches VCC(on) level, the controller
internal logic starts and thus, first DRV pulse is authorized
after the safety period of 200 ms passes. But the last DRV
pulse can comes just before VCC(min) level. Therefore, there
are extended rules to generation and cancellation the armed
flag to avoid the false pre−short condition if the controller
can’t start properly because of the grounded FB pin.
The NCP12510 offers the operation mode when the
NCP12510 could be controlled by Master system via
Feedback pin (pin 2). When FB pin is grounded, the
controller driver pulses are stopped. This is the same
situation, when the controller is in skip mode, but with the
difference that FB pin could be forced to ground by Master
system anytime during operation, even at start−up sequence.
latched
VFB (t)
new sequence
latched
new sequence
latched
[email protected]
gnd
[email protected]
t
VCC (t)
VCC(on)
VCC(latch_hyst)
VCC(min)
VCC(reset)
t
[email protected]
AND
armed flag
[email protected]
AND
armed flag
VDRV (t)
Armed flag
1
0
t
1
1
Grounded [email protected](on)
→ No Armed flag
UVLO
AND
Armed
flag
Grounded FB @first goingdown V CC cycle → Double
hiccup → switching
allowed every odd V CC(on)
t
VCS (t)
Vlimit
t
Figure 54. The controller start−up sequence with grounded FB pin and Pre−short condition.
auto-recovery new sequence auto-recovery
auto-recovery
VFB (t)
[email protected]
gnd
[email protected]
gnd
[email protected]
gnd
[email protected]
gnd
t
VCC (t)
VCC(on)
VCC(min)
VCC(reset)
t
VDRV (t)
UVLO and
NO armed flag
UVLO and
NO armed flag
UVLO
t
1
Armed flag
1
1
1
1
0
VCS (t)
t
8 cycles
8 cycles
Vlimit
t
Figure 55. The controller behaviour during start−up sequence interupted by grounded FB pin.
www.onsemi.com
21
NCP12510
– this is the second armed flag cancelation condition. The
Figure 55 shows the cases of interrupted start−up sequence
by grounded FB pin.
If the start−up sequence is interrupted by grounded FB
pin, the armed flag is canceled. Then, if UVLO comes, the
controller newly starts after double−hiccup auto−recovery
sequence. Then, if UVLO comes again, the controller is
latched off.
The Figure 56 shows the case of operation, when the
controller can operate under some master system with
superordinate function. Then, the FB pin is used for
authorization or denial DRV pulses. If the normal operation
state is interrupted for a long time and afterwards the
soft−start is demanded for proper start−up of power supply,
the VCC have to be pulled−down below VCC(reset) level.
Then, if the FB isn’t grounded, the new start−up sequence
are initialized when VCC touches VCC(on) level + 200 ms
safety period. During this new start−up sequence is
generated the armed flag.
The armed flag is generated with first DRV pulse, but only
if the first DRV pulse is synchronized with VCC(on) event. If
the FB pin is forced to ground during the VCC(on) event and
it is released afterwards, the armed flag is not generated. The
Figure 54 shows the cases of grounded FB pin at the
beginning of start−up sequence.
If the armed flag isn’t active and UVLO comes, the
controller newly starts after double−hiccup auto−recovery
sequence. Then, if UVLO comes again, the controller is
latched off. DRV pulses are authorized during the whole first
VCC going−down cycle. If any DRV pulse doesn’t come
during this time, the double−hiccup auto−recovery sequence
is coming.
The armed flag could be canceled by two conditions.
When the controller gets into regulation after start−up
sequence, i.e. during the eight consecutive switching cycles
is current setpoint voltage under Vlimit , the armed flag is
called off – this is the first armed flag cancelation condition.
When the start−up sequence isn’t complete and is
interrupted by grounded FB pin, the armed flag is called off
new sequence
VFB (t)
[email protected]
gnd
[email protected]
gnd
[email protected]
gnd
t
VCC (t)
VCC(on)
Supply voltage V CC is
The IC must be reset to
ensure the soft -start
after release the FB
Stop DRV pulses by
Master Sytem
controlled by Master System
VCC(min)
VCC(reset)
t
VDRV (t)
Armed
flag
t
1
Grounded FB @VCC(on)
→ No Armed flag
0
VCS (t)
8 cycles
8 cycles
1
8 cycles
t
Vlimit
t
Figure 56. The Master system driving the controller by forcing the FB pin to ground.
Slope Compensation
half the switching frequency and occur only during
Continuous Conduction Mode (CCM) with a duty ratio
greater than 50%. To lower the current loop gain, one usually
injects between 50 and 100% of the primary inductance
downslope. Figure 57 depicts how the ramp is generated
internally. Please note that the ramp signal will be
disconnected from the CS pin during the off−time.
The NCP12510 includes an internal slope compensation
signal. This is the buffered oscillator clock delivered during
the on−time only. Its amplitude is around 2.5 V at the
maximum duty ratio. Slope compensation is a known means
used to cure sub harmonic oscillations in CCM−operated
current−mode converters. These oscillations take place at
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22
NCP12510
2.5 V
0V
Dmax
TSW
Driver
reset
ON time
Rramp
20 kΩ
+
tLEB
_
CS
Rcomp
Rsense
From FB
Figure 57. Inserting a resistor in series with the current sense information brings slope compensation and
stabilizes the converter in CCM operation.
current sense pin to the controller ground for an improved
immunity to the noise. Please make sure both components
are located very close to the controller.
In the NCP12510 controller, the oscillator ramp features
a 2.5 V swing. If the clock operates at a 65 kHz frequency,
then the available oscillator slope corresponds to:
S ramp +
V ramp,peak
D max @ T SW
+
2.5
+ 208 mVńms (eq. 10)
0.8 @ 15 m
Latching Off the Controller
The OPP pin not only allows a reduction of the peak
current set point in relationship to the line voltage, it also
offers a means to permanently latch−off the part. When the
part is latched−off, all pulses are immediately stopped and
VCC hiccups from VCC(min) voltage level with hysteresis
VCC(latch_hyst) until a reset occurs (VCC falls down below
level VCCreset ), e.g. by un−plugging the converter from the
mains outlet. The VCC hysteresis helps significantly reduce
the reset time, because when the user unplugged the adapter
from the outlet in the less favourable time (VCC is in its
maximum), the VCC has to fall down from voltage level
given by 480 mV + 250 mV typically to reset level.
The latch detection is made by observing the OPP pin by
a comparator featuring a Vlatch reference voltage. However,
for noise reasons and in particular to avoid the leakage
inductance contribution at turn off, a blanking delay
tlatch−blank is introduced before the output of the OVP
comparator is checked. Then, the OVP comparator output is
validated only if its high−state duration lasts for a minimum
time tlatch−del . Below this value, the event is ignored. Then,
a counter ensures that only 4 successive OVP events have
occurred before actually latching the part. There are several
possible implementations, depending on the needed
precision and the parameters you want to control.
The first and easiest solution is the additional resistive
divider on top of the OPP one. This solution is simple and
inexpensive but requires the insertion of a diode to prevent
disturbing the OPP divider during the on−time.
In our flyback design, let’s assume that our primary
inductance Lp is 770 mH, and the SMPS delivers 19 V with
a Np :Ns ratio of 1:0.25. The off−time primary current slope
Sp is thus given by:
Sp +
ǒVout ) VfǓ @ NNs
p
Lp
+
(19 ) 0.7) @ 4
+ 102 mAńms
770 m
(eq. 11)
Given a sense resistor of 330 mW, the above current ramp
turns into a voltage ramp of the following amplitude:
S sense + S p @ R sense + 102 m @ 0.33 + 34 mVńms
(eq. 12)
If we select 50% of the downslope as the required amount
of slope compensation, then we shall inject a ramp whose
slope is 17 mV/ms. Our internal compensation being of
208 mV/ms, the divider ratio (divratio) between Rcomp and
the internal Rramp = 20 kW resistor is:
divratio +
0.5 @ S sense
+ 0.082
S ramp
(eq. 13)
The series compensation resistor value is thus:
R comp + R ramp @ divratio + 20 k @ 0.082 + 1.64 kW
(eq. 14)
A resistor of the calculated value will then be inserted
from the sense resistor to the current sense pin. We
recommend adding a small capacitor of 100 pF, from the
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23
NCP12510
Vlatch (t)
The IC is latched after the fault is confirmed for 4
consecutive DRV cycles
Vlatch
The user unplugged and plugged
the adapter to the outlet
t
VCC (t)
VCC(on)
VCC(latch_hyst)
VCC(min)
VCC(reset)
t
VDRV (t)
The time needs for IC reset is
significantly shorter due to the
VCC hysteresis used in latch mode .
t
Figure 58. Latching off the controller and resuming operation.
ROVP
D1
ROPPU
V CC
+
100p
ROPPL
OPP/
Latch
+
+
_
C1
OVP
Vlatch
aux.
winding
OPP
Figure 59. A simple resistive divider brings the OPP pin above 3 V in case of a VCC voltage runaway above 18 V.
First, calculate the OPP network with the above equations.
Then, suppose we want to latch off our controller when Vout
exceeds 25 V. On the auxiliary winding, the plateau reflects
the output voltage by the turns ratio between the power and
the auxiliary winding. In case of voltage runaway for our
19 V adapter, the plateau will go up to:
V aux,OVP + V out @
Ns
+ 25 @ 0.18 + 18 V
0.25
N aux
R OVP + V out @
VOVP
ROPPL
+ 18 * 3 + 5 kW
3
(eq. 16)
1k
In nominal conditions, the plateau establishes to around
14 V. Given the divide by 6 ratio, the OPP pin will swing to
14/6 = 2.3 V during normal conditions, leaving 700 mV for
the noise immunity. A 100 pF capacitor can be added to
improve it and avoid erratic trips in presence of external
surges. Do not increase this capacitor too much otherwise the
OPP signal will be affected by the integrating time constant.
A second solution for the OVP detection alone is to use a
Zener diode wired as recommended by Figure 60.
(eq. 15)
Since our OVP comparator trips at level Vlatch = 3 V,
across the 1 kW selected OPP pull−down resistor, it implies
a 3 mA current. From 3 V to go up to 18 V, we need an
additional 15 V. Under 3 mA and neglecting the series diode
forward drop, it requires a series resistor of:
15 V
V aux,OVP * V latch
D1
R OPPU
V CC
+
R OPPL
+
+
_
C1
22p
OPP /
Latch
V latch
OVP
aux .
winding
OPP
Figure 60. A Zener diode in series with a diode helps to improve the noise immunity of the system.
www.onsemi.com
24
NCP12510
In this case, to still trip at 18 V level, we have selected a
15 V Zener diode. In nominal conditions, the voltage on the
OPP pin is almost 0 V during the off−time as the Zener is
fully blocked. This technique clearly improves the noise
immunity of the system compared to that obtained from a
resistive string as in Figure 59. Please note the reduction of
the capacitor on the OPP pin to 10−22 pF. This is because of
the potential spike going through the Zener parasitic
capacitor and the possible auxiliary level shortly exceeding
its breakdown voltage during the leakage inductance reset
period (hence the internal blanking delay tlatch−blank at turn
off). This spike despite its very short time is energetic
enough to charge the added capacitor C1 and given the time
constant, could make it discharge slower, potentially
NTC
disturbing the blanking circuit. When implementing the
Zener option, it is important to carefully observe the OPP pin
voltage (short probe connections!) and check that enough
margin exists to that respect.
Over Temperature Protection
In a lot of designs, the adapter must be protected against
thermal runaways, e.g. when the temperature inside the
adapter box increases a certain value. Figure 61 shows how
to implement a simple OTP using an external NTC and a
series diode. The principle remains the same: make sure the
OPP network is not bothered by the additional NTC hence
the presence of this diode.
D1
ROPPU
VCC
+
+
+
_
ROPPL
OPP/
Latch
OVP
Vlatch
aux.
winding
OPP
Figure 61. The internal circuitry hooked to OPP/Latch pin can be used to implement over temperature protection
(OTP).
200 mV decrease from the Vlimit setpoint and the on−time
swing on the auxiliary anode is −67.5 V, then we need to drop
over ROPPU a voltage of:
When the NTC resistor will diminish as the temperature
increases, the voltage on the OPP pin during the off−time
will slowly increase and, once it passes Vlatch level for 4
consecutive clock cycles, the controller will permanently
latch off.
Back to our 19 V adapter, we have found that the plateau
voltage on the auxiliary diode was 14 V in nominal
conditions. We have selected an NTC which offers a 470 kW
resistance at 25°C and drops to 8.8 kW at 110°C. If our
auxiliary winding plateau is 14 V and we consider a 0.7 V
forward drop for the diode, then the voltage across the NTC
in fault mode must be:
VR
OPPU
The current circulating the pull down resistor ROPPL in this
condition will be:
IR
Based on the 8.8 kW NTC resistor at 110°C, the current
inside the device must be:
V latch
+ 2.5 kW
I NTC
V OPP
+ −0.2 + −80 mA
R OPPL
2.5 k
(eq. 21)
VR
IR
OPPU
OPPU
+ −67.3 [ 841 kW
−80 m
(eq. 22)
Combining OVP and OTP
The OTP and Zener−based OVP can be combined
together as illustrated by Figure 62. In nominal VCC/output
conditions, when the Zener is not activated, the NTC can
drive the OPP pin and trigger the adapter in case of a fault.
On the contrary, in nominal temperature conditions, if the
loop is broken, the voltage runaway will be detected and
acknowledged by the controller.
In case the OPP pin is not used for either OPP or OVP, it
can simply be grounded.
(eq. 18)
As such, the bottom resistor ROPPL , can easily be calculated:
R OPPL +
+
R OPPU +
(eq. 17)
I NTC +
+ 10.3 + 1.2 mA
R NTC(110)
8.8 k
OPPL
The ROPPU value is therefore easily derived:
V NTC + V aux * V latch * V F + 14 * 3 * 0.7 + 10.3 V
V NTC
+ V aux * V OPP + −67.5 ) 0.2 + −67.3 V (eq. 20)
(eq. 19)
Now the pull down OPP resistor is known, we can
calculate the upper resistor value ROPPU to adjust the power
limit at the chosen output power level. Suppose we need a
www.onsemi.com
25
NCP12510
15 V
D1
NTC
R OPPU
V CC
+
+
+
aux.
winding
_
R OPPL
OPP /
Latch
OVP
V latch
OPP
Figure 62. With the NTC back in place, the circuit nicely combines OVP, OTP and OPP on the same pin.
Filtering the Spikes
recommend the installation of a small RC filter before the
detection network as illustrated by Figure 63. The values of
resistance and capacitance must be selected to provide the
adequate filtering function without degrading the stand−by
power by an excessive current circulation.
The auxiliary winding is the seat of spikes that can couple
to the OPP pin via the parasitic capacitances exhibited by the
Zener diode and the series diode. To prevent an adverse
triggering of the Over Voltage Protection circuitry, we
15 V
NTC
D1
Additional filter
R OPPU
R1
C1
+
+
+
_
R OPPL
OPP/
Latch
V latch
V CC
OVP
aux.
winding
OPP
Figure 63. A small RC filter prevents the fast rising spikes from reaching the protection pin OPP/latch in presence
of energetic perturbations superimposed on the input line.
Parameters Options
Second adjustable parameter is over voltage protection
threshold on VCC pin – VOVP. Default value of VOVP is
25.5 V. Other option is 32 V.
Third adjustable parameter is internal fault timer – tfault .
Default value of tfault is 115 ms. Other possible options are
23 ms, 60 ms and 460 ms. Guaranteed dispersion of this
parameter is ±15% for min and max marginal values.
This chapter deals with options of the parameters which
could be change on the current silicon upon customer
request.
First adjustable parameter is frozen internal peak current
setpoint – VCS(freeze) . This parameter determines the
efficiency vs. acoustic noise performance for light loads.
Default value of VCS(freeze) is set at 250 mV (≈31% of Vlimit).
Other possible options are 275 mV (≈34% of Vlimit) and
300 mV (≈38% of Vlimit).
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26
NCP12510
PACKAGE DIMENSIONS
TSOP−6
CASE 318G−02
ISSUE V
D
H
6
5
ÉÉ
E1
1
2
4
L2
GAUGE
PLANE
E
3
NOTE 5
L
M
b
C
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. MAXIMUM LEAD THICKNESS INCLUDES LEAD FINISH. MINIMUM
LEAD THICKNESS IS THE MINIMUM THICKNESS OF BASE MATERIAL.
4. DIMENSIONS D AND E1 DO NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH, PROTRUSIONS, OR
GATE BURRS SHALL NOT EXCEED 0.15 PER SIDE. DIMENSIONS D
AND E1 ARE DETERMINED AT DATUM H.
5. PIN ONE INDICATOR MUST BE LOCATED IN THE INDICATED ZONE.
SEATING
PLANE
DETAIL Z
e
A
0.05
c
A1
DETAIL Z
DIM
A
A1
b
c
D
E
E1
e
L
L2
M
MIN
0.90
0.01
0.25
0.10
2.90
2.50
1.30
0.85
0.20
0°
MILLIMETERS
NOM
MAX
1.00
1.10
0.06
0.10
0.38
0.50
0.18
0.26
3.00
3.10
2.75
3.00
1.50
1.70
0.95
1.05
0.40
0.60
0.25 BSC
10°
−
STYLE 13:
PIN 1. GATE 1
2. SOURCE 2
3. GATE 2
4. DRAIN 2
5. SOURCE 1
6. DRAIN 1
RECOMMENDED
SOLDERING FOOTPRINT*
6X
0.60
6X
3.20
0.95
0.95
PITCH
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
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NCP12510/D