ETC NCP1561/D

NCP1561
Push−Pull PWM Controller
for 48 V Telecom Systems
The NCP1561 Push−Pull PWM controller contains all the features
and flexibility needed to implement high efficiency dc−dc converters
using voltage or current−mode control. This device can be configured
in any dual ended topology such as push−pull or half−bridge. It can
also be used for forward topologies requiring a 50% maximum duty
cycle. This device is ideally suited for 48 V telecom, 42 V automotive
systems and 12 V input applications.
The NCP1561 cost effectively reduce system part count by
incorporating a high voltage start−up regulator, line undervoltage
detector, single resistor oscillator setting, dual mode overcurrent
protection, soft start and single resistor feedforward ramp generator.
The oscillator frequency can be adjusted up to 250 kHz.
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MARKING
DIAGRAM
16
SO−16
D SUFFIX
CASE 751B
16
1
1
Features
•
•
•
•
•
•
•
•
•
•
•
•
NCP1561
AWLYWW
NCP1561 = Device Code
A
= Assembly Location
WL
= Wafer Lot
Y
= Year
WW
= Work Week
Internal High Voltage Start−up Regulator
Minimum Operating Voltage of 21.5 V
Voltage or Current−Mode Control Capability
Single Resistor Oscillator Frequency Setting
Adjustable Frequency up to 250 kHz
Fast Line Feedforward
Line Undervoltage Lockout
Dual Mode Overcurrent Protection
Programmable Maximum Duty Cycle Control
Maximum Duty Cycle Proportional to Line Voltage
Programmable Soft Start
Precision 5.0 V Reference
PIN ASSIGNMENTS
Vin
VAUX
UV
OUT1
RAMP_OUT
GND
FF
OUT2
CS
RAMP_IN
CSKIP
VREF
RT
VEA
DCMAX
SS
Typical Applications
• 48 V Telecommunication Power Converters
• Industrial Power Converters
• 42 V Automotive Systems
Device
NCP1561DR2
M4
+
C1
−
C2
Start−up
OUT2
OUT1
Shipping†
SO−16
2500 Units/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.
OUT1
Feedforward
NCP1561
Package
TX1
M2
Vin
ORDERING INFORMATION
Lout
M3
Cout
High Side
Driver
Driver
M1
OUT2
Opto
Error
Amplifier
Figure 1. Half−Bridge Block Diagram
 Semiconductor Components Industries, LLC, 2004
February, 2004 − Rev. 2
1
Publication Order Number
NCP1561/D
NCP1561
Vin
VAUX
High Voltage
Start−up
Regulator
5.0 V
Reference
VREF
Thermal
Shutdown
UV
CS
UV
Fault
Detection
OUT1
Modulator
Output
Stage
OUT2
CSKIP
RT
Oscillator
VEA
FF
SS
GND
DCMAX
RAMP_OUT
RAMP_IN
Figure 2. Simplified Block Diagram
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2
NCP1561
VAUX
1
Vin
5.0 V Reference
DIS
Disable
IAUX
VAUX(on)
−
+
VREF
11
Disable_VREF
16
One Shot
Pulse
(250 ns)
VAUX
CAUX
+
Output Latch
S
VAUX(on)/VAUX(off)
Dominant
Reset Q
Latch
−
Vin
R
Thermal
Shutdown
2
UV
+
−
STOP
−
+
Enable_ss
1.52 V
VAUX
VREF
15
12 A
−
+
S
Clock
6
−
+
+
2V
−
CCSKIP
One Shot
Pulse
(600 ns)
CS
2 k
+
− +
6 A
Enable_ss
VEA
RAMP_IN
2V
Max DC
Comparator
−
Oscillator Ramp
I1
2
I1
9
2V
29 k
VREF
RMDP
+
29 k
8
VDC(inv)
−
SS
CSS
DCMAX
RP
38 k
STOP
+
−
10 pF
7
+
2V
−
+
* Trimmed during
manufacturing to obtain
1.3 V with RT = 101 k
−
2V
Clock
Vin
FF
I
5.3 k
IFF
REA
10
12
Softstart
Comparator
CURRENT MIRROR
4
OUT2
20 k
VREF
RFF
13
PWM
Comparator
−
+
1.0 V
−
RT
VAUX
VREF
+
−
+
1.3 V*
−
OUT1
Q
+
−
+
1.2 V
−
5
RT
TF/F Q
Q
Dominant
Reset
Latch
R
+
CSKIP
Disable
6.7 k
V
125 k
+
+
V
−
One Shot
Pulse
FF Ramp
(Adjustable)
3
Buffer
−
10.8 pF
CFF
Figure 3. NCP1561 Block Diagram
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3
RAMP_OUT
NCP1561
PIN DESCRIPTION
Pin
Name
Application Information
1
Vin
This pin is connected to the bulk DC input voltage supply. A constant current source supplies current from
this pin to the capacitor connected on the VAUX pin. The charge current is typically 13.0 mA. Input voltage
range is 21.5 V to 150 V.
2
UV
Input supply voltage is scaled down and sampled by means of a resistor divider. The supply voltage must be
scaled such that the voltage on the UV pin is 1.54 V at the minimum input voltage.
3
RAMP_OUT
4
FF
An external resistor between Vin and this pin adjusts the amplitude of the FF Ramp inversely proportional to
Vin. By varying the Feedforward Ramp amplitude in proportion to the input voltage, changes in loop
bandwidth resulting from Vin changes are eliminated.
5
CS
Overcurrent sense input. If the CS voltage exceeds 0.95 V or 1.15 V, the converter enters the Cycle by Cycle
or Cycle Skip current limit mode, respectively.
6
CSKIP
The capacitor connected to this pin sets the Cycle Skip period. Once a cycle skip fault is detected, the
capacitor connected to this pin is discharged. The capacitor is then charged with a constant current of 12 A.
The cycle skip period expires, once the voltage on this capacitor reaches 2.0 V. A soft start sequence follows
at the conclusion of the fault period.
7
RT
8
DCMAX
9
SS
An internal 6.0 µA current source charges the external capacitor connected to this pin. The duty cycle is
limited during start−up by comparing the voltage on this pin to the Oscillator Ramp. The soft start comparator
limits the duty cycle while the SS voltage is below 2.0 V.
10
VEA
The error signal from an external error amplifier is fed into this input and compared to the Feedforward Ramp.
A series diode and resistor offset the voltage on this pin before it is applied to the PWM Comparator inverting
input.
11
VREF
Precision 5.0 V reference output. Maximum output current is 6.0 mA.
12
RAMP_IN
13
OUT2
Output 2.
14
GND
Control circuit ground.
15
OUT1
Output 1.
16
VAUX
Positive input supply voltage. This pin is connected to an external capacitor for energy storage. An internal
current source supplies current from Vin to this pin. Once the voltage on VAUX reaches approximately 10.3 V,
the current source turns OFF. It turns ON again once VAUX falls to 7 V. During normal operation, power is
supplied to the IC via this pin, by means of an auxiliary winding. The start−up circuit is disabled if the voltage
on the VAUX pin exceeds 10.3 V.
Internal Feedforward (FF) Ramp Output. This signal can be externally routed to the RAMP_IN pin for
voltage−mode control operation.
A single external resistor between this pin and GND sets the fixed oscillator frequency.
An external resistor between this pin and GND sets the voltage on the Max DC Comparator inverting input.
The duty cycle is limited by comparing the voltage on the Max DC Comparator inverting input to the
Feedforward Ramp.
This pin configures the NCP1561 for voltage or current−mode control. The internal Feedforward Ramp
(voltage−mode) or a signal proportional to the inductor current (current−mode) is fed into this input and
compared to the signal in the VEA pin.
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4
NCP1561
MAXIMUM RATINGS (Note 1)
Rating
Symbol
Value
Unit
Vin
−0.3 to 150
V
Auxiliary Supply Voltage
VAUX
−0.3 to 16
V
Auxiliary Supply Input Current
IAUX
35
mA
OUT1 and OUT2 Voltage
VOUT
−0.3 to (VAUX + 0.3 V)
V
OUT1 and OUT2 Output Current
IOUT
10
mA
5.0 V Reference Voltage
VREF
−0.3 to 6.0
V
5.0 V Reference Output Current
IREF
6.0
mA
All Other Inputs/Outputs Voltage
VIO
−0.3 to VREF
V
All Other Inputs/Outputs Current
IIO
10
mA
Operating Junction Temperature
TJ
−40 to 150
C
Storage Temperature Range
Tstg
−55 to 150
C
Power Dissipation at TA = 25°C
PD
0.77
W
RθJA
130
C/W
Input Line Voltage
Thermal Resistance, Junction to Ambient
1. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously.
If stress limits are exceeded device functional operation is not implied, damage may occur and reliability may be affected. Functional
operation should be restricted to the Recommended Operating Conditions.
A. This device series contains ESD protection and exceeds the following tests:
Pin 1: Pin 1 is the HV start−up of the device and is rated to the max rating of the part, or 150 V.
Machine Model Method 150 V.
Pins 2−16: Human Body Model 2000 V per MIL−STD−883, Method 3015.
Machine Model Method 200 V.
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5
NCP1561
ELECTRICAL CHARACTERISTICS (Vin = 48 V, VAUX = 12 V, VEA = 2 V, RT = 101 k, CCSKIP = 6800 pF, RD = 60.4 k,
RFF = 432 k, for typical values TJ = 25°C, for min/max values, TJ = −40°C to 125°C, unless otherwise noted)
Symbol
Min
Typ
Max
VAUX(on)
VAUX(off)
VH
9.7
6.6
−
10.3
7.0
3.3
10.8
7.4
−
VSTART(min)
−
18.3
21.5
Characteristic
Unit
START−UP CONTROL AND VAUX REGULATOR
VAUX Regulation
Startup Threshold/VAUX Regulation Peak (VAUX increasing)
Minimum Operating VAUX Valley Voltage After Turn−On
Hysteresis
V
Minimum Start−up Voltage (Pin 1)
ISTART = 1.0 mA, IREF = 0 mA, VAUX = VAUX(on) − 0.2 V
Start−up Circuit Output Current
VAUX = 0 V
TJ = 25°C
TJ = −40°C to 125°C
VAUX = VAUX(on) − 0.2 V
TJ = 25°C
TJ = −40°C to 125°C
ISTART
Start−up Circuit Off−State Leakage Current (Vin = 150 V)
TJ = 25°C
TJ = −40°C to 125°C
mA
13
10
17
−
21
25
10
8.0
13
−
17
19
−
−
23
−
50
100
150
−
−
A
ISTART(off)
Start−up Circuit Breakdown Voltage (Note 2)
ISTART(off) = 50 A, TJ = 25°C
VBR(DS)
Auxilliary Supply Current After VAUX Turn−On
Outputs Disabled
VEA = 0 V
VUV = 0 V
Outputs Enabled
V
V
mA
IAUX1
IAUX2
IAUX3
−
−
−
3.3
1.8
4.1
5.0
2.5
6.5
VUV
1.40
1.54
1.64
V
VUV(H)
0.080
0.095
0.120
V
tUV
−
250
−
ns
Cycle by Cycle Threshold Voltage
ILIM1
0.89
0.95
1.03
V
Propagation Delay to Output (VEA = 2.0 V)
VCS = ILIM1 to 2.0 V, measured when OUT1 reaches 10 V.
tILIM
−
86
150
ns
Cycle Skip Threshold Voltage
ILIM2
1.05
1.15
1.24
V
Cycle Skip Charge Current (VCSKIP = 0 V)
ICSKIP
8.0
12.3
15
A
Thermal Shutdown Threshold (Junction Temperature Increasing, Note 2)
TSHDN
−
180
−
°C
Thermal Shutdown Hysteresis (Junction Temperature Decreasing, Note 2)
TH
−
17
−
°C
LINE UNDERVOLTAGE DETECTOR
Undervoltage Threshold (Vin Increasing)
Undervoltage Hysteresis
Undervoltage Propagation Delay to Output
CURRENT LIMIT AND THERMAL SHUTDOWN
2. Guaranteed by design only.
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6
NCP1561
ELECTRICAL CHARACTERISTICS (Vin = 48 V, VAUX = 12 V, VEA = 2 V, RT = 101 k, CCSKIP = 6800 pF, RD = 60.4 k,
RFF = 432 k, for typical values TJ = 25°C, for min/max values, TJ = −40°C to 125°C, unless otherwise noted) (continued)
Symbol
Characteristic
Min
Typ
Max
143
137
150
−
157
163
228
220
240
−
252
260
Unit
CONTROL OUTPUTS
Frequency (RT = 101 k)
TJ = 25°C
TJ = −40°C to 125°C
fOSC1
Frequency (RT = 59 k)
TJ = 25°C
TJ = −40°C to 125°C
fOSC2
kHz
kHz
Output Voltage (IOUT = 0 mA)
Low State
High State
VOL
VOH
−
−
0.25
11.8
−
−
V
Drive Resistance (Vin = 15 V)
Sink (VEA = 0 V, VOUT = 2 V)
Source (VEA = 3 V, VOUT = 10 V)
RSNK
RSRC
20
50
36
88
80
170
Rise Time (CL = 100 pF, 10% to 90% of VOH)
ton
−
32
−
ns
Fall Time (CL = 100 pF, 90% to 10% of VOH)
toff
−
19
−
ns
34
48
38
−
44
50
MAXIMUM DUTY CYCLE COMPARATOR
Maximum Duty Cycle (Vin = 36 V)
RP = 0 , RMDP = open
RP = open, RMDP = open (Note 3)
DCMAX
%
Open Circuit Voltage
VDCMAX
0.49
0.74
0.90
V
Charge Current (VSS = 1.0 V)
ISS(C)
5.0
6.2
7.4
A
Discharge Current (VSS = 5.0 V, VUV = 1.0 V)
ISS(D)
20
50
−
mA
RIN(VEA)
8.0
22
60
k
Lower Input Threshold
VEA(L)
0.7
0.92
1.1
V
Delay to Output (from VOH to 0.5 VOH)
tPWM
−
200
−
ns
4.9
4.8
4.96
−
5.1
5.1
SOFT START
PWM COMPARATOR
Input Resistance (V1 = 1.25 V, V2 = 1.50 V)
RIN(VEA) = (V2 − V1) / (I2 − I1)
5.0 V REFERENCE
Output Voltage (IREF = 0 mA)
TJ = 25°C
TJ = −40°C to 125°C
VREF
V
Load Regulation (IREF = 0 to 6 mA)
VREF(Load)
−
10
50
mV
Line Regulation (VAUX = 7.5 V to 16 V)
VREF(Line)
−
50
100
mV
3. 50% Maximum Duty Cycle guaranteed by design.
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7
NCP1561
19
ISTART, START−UP CIRCUIT OUTPUT
CURRENT (mA)
12
11
10
START−UP
THRESHOLD
9
8
7
MINIMUM
OPERATING
THRESHOLD
6
5
−50
−25
0
25
50
75
100
125
150
18
Vin = 48 V
17
16
VAUX = 0 V
15
14
13
12
VAUX = VAUX(on) − 0.2 V
11
10
9
−50
−25
0
25
50
75
100
125
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 4. Auxiliary Supply Voltage Thresholds
versus Junction Temperature
Figure 5. Start−up Circuit Output Current
versus Junction Temperature
ISTART, START−UP CIRCUIT OUTPUT
CURRENT (mA)
17.5
Vin = 48 V
17.0
16.5
16.0
15.5
15.0
14.5
14.0
13.5
13.0
12.5
0
2
4
6
8
10
TJ = −40°C
12
TJ = 25°C
TJ = 125°C
8
4
VAUX = VAUX(on) − 0.2 V
0
0
25
50
75
100
125
Vin, LINE VOLTAGE (V)
Figure 6. Start−up Circuit Output Current
versus Auxiliary Supply Voltage
Figure 7. Start−up Circuit Output Current
versus Line Voltage
VAUX = 12 V
TJ = −40°C
35
30
25
TJ = 25°C
20
TJ = 125°C
15
10
5
0
0
16
VAUX, AUXILIARY SUPPLY VOLTAGE (V)
40
25
50
75
100
125
150
150
4.5
VAUX = 12 V
4.0
3.5
VEA = 0 V
3.0
2.5
2.0
VUV = 0 V
1.5
1.0
0.5
−50
−25
0
25
50
75
100
125 150
Vin, LINE VOLTAGE (V)
TJ, JUNCTION TEMPERATURE (°C)
Figure 8. Start−up Circuit Off−State Leakage
Current versus Line Voltage
Figure 9. Auxiliary Supply Current versus
Junction Temperature
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8
150
20
12
IAUX, AUXILIARY SUPPLY CURRENT (mA)
ISTART(off), START−UP CIRCUIT OFF−
STATE LEAKAGE CURRENT (A)
ISTART, START−UP CIRCUIT OUTPUT
CURRENT (mA)
VAUX, AUXILIARY SUPPLY VOLTAGE (V)
TYPICAL CHARACTERISTICS
NCP1561
TYPICAL CHARACTERISTICS
1.70
VAUX = 12 V
DC 50%
5.5
VUV, LINE UNDERVOLTAGE
THRESHOLD (V)
IAUX3, OPERATING AUXILIARY
SUPPLY CURRENT (mA)
6.0
fOSC = 250 kHz
5.0
4.5
fOSC = 150 kHz
4.0
3.5
3.0
−25
0
25
50
75
100
125
1.50
1.45
1.40
−25
0
25
50
75
100
125
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 10. Operating Auxiliary Supply Current
versus Junction Temperature
Figure 11. Line Undervoltage Threshold
versus Junction Temperature
ILIM, CURRENT LIMIT THRESHOLDS (V)
VUV(H), LINE UNDERVOLTAGE
THRESHOLD HYSTERESIS (mV)
1.55
1.30
−50
150
140
130
120
110
100
90
80
70
−50
−25
0
25
50
75
100
125
150
1.25
1.20
CYCLE SKIP
1.15
1.10
1.05
1.00
CYCLE BY CYCLE
0.95
0.90
−50
−25
0
25
50
75
100
125 150
TJ, JUNCTION TEMPERATURE (°C)
Figure 12. Line Undervoltage Hysteresis versus
Junction Temperature
Figure 13. Current Limit Thresholds versus
Junction Temperature
VAUX = 12 V
110
Measured from VOH to 0.5 VOH
fosc, OSCILLATOR FREQUENCY (kHz)
115
105
100
95
90
85
80
75
70
−50
−25
0
25
50
75
100
125
150
300
275
RT = 50.6 k
250
225
200
175
RT = 101 k
150
125
RT = 148 k
100
75
−50
−25
0
25
50
75
100
125
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 14. Current Limit Propagation Delay
versus Junction Temperature
Figure 15. Oscillator Frequency versus
Junction Temperature
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9
150
1.30
TJ, JUNCTION TEMPERATURE (°C)
120
tILIM, CURRENT LIMIT
PROPAGATION DELAY (ns)
1.60
1.35
fOSC = 100 kHz
2.5
−50
1.65
150
NCP1561
fosc, OSCILLATOR FREQUENCY (kHz)
157.5
RT = 101 k
155.0
152.5
150.0
147.5
145.0
142.5
−50
−25
0
25
50
75
100
125
300
200
150
100
50
0
50
100
250
300
350
RT, TIMING RESISTOR (k)
Figure 17. Oscillator Frequency versus
Timing Resistor
80
70
100
90
RSRC (VEA = 0 V, VOUT = 10 V)
80
70
60
50
40
RSNK (VEA = 3 V, VOUT = 2 V)
Measured from 10% to 90% of VOH
VAUX = 12 V
60
400
TJ = 125°C
TJ = 25°C
50
40
30
TJ = −40°C
20
10
0
−25
0
25
50
75
100
125
150
0
25
TJ, JUNCTION TEMPERATURE (°C)
TJ = 25°C
20
TJ = −40°C
15
10
5
0
25
50
75
100
125
150
175
200
FEEDFORWARD INTERNAL RESISTANCE (k)
Measured from 90% to 10% of VOH
30 VAUX = 12 V
TJ = 125°C
75
100
125
150
175
200
Figure 19. Outputs Rise Time versus Load
Capacitance
35
25
50
CL, LOAD CAPACITANCE (pF)
Figure 18. Outputs Drive Resistance versus
Junction Temperature
toff, OUTPUTS FALL TIME (ns)
200
TJ, JUNCTION TEMPERATURE (°C)
110 VAUX = 12 V
0
150
Figure 16. Oscillator Frequency versus
Junction Temperature
120
30
20
−50
TJ = 25°C
DC 50%
250
150
ton, OUTPUTS RISE TIME (ns)
RSNK/SRC OUTPUTS DRIVE RESISTANCE ()
fosc, OSCILLATOR FREQUENCY (kHz)
TYPICAL CHARACTERISTICS
19
18
17
16
15
14
13
12
11
10
9
−50
−25
0
25
50
75
100
125
CL, LOAD CAPACITANCE (pF)
TJ, JUNCTION TEMPERATURE (°C)
Figure 20. Outputs Fall Time versus Load
Capacitance
Figure 21. Feedforward Internal Resistance
versus Junction Temperature
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10
150
NCP1561
VEA = 3.0 V
DCMAX PIN = OPEN
45
40
35
30
TJ = 125°C
25
20
15
TJ = −40°C
10
5
0
0
75
150
225
300
450
375
525
40
RP = 0 , RMDP = OPEN
35
30
25
20
−50
−25
0
25
50
75
100
125
Figure 23. Maximum Duty Cycle versus
Junction Temperature
6.5
65
CHARGE
6.0
60
5.5
55
DISCHARGE
50
4.5
45
4.0
40
3.5
35
−25
0
25
50
75
30
125 150
100
TJ, JUNCTION TEMPERATURE (°C)
40
30
20
10
0
−50
−25
0
25
50
75
100
125 150
TJ, JUNCTION TEMPERATURE (°C)
Figure 25. VEA Input Resistance versus
Junction Temperature
5.01
1.00
VREF, REFERENCE VOLTAGE (V)
RFF = 432 k
Vin = 48 V
0.95
0.90
0.85
0.80
0.75
−50
150
50
Figure 24. Soft Start Charge/Discharge
Currents versus Junction Temperature
VEA(L), PWM COMPARATOR LOWER
INPUT THRESHOLD (V)
Vin = 36 V
RFF = 432 k
Figure 22. Maximum Duty Cycle versus
Feedforward Current
70
3.0
−50
RP = OPEN, RMDP = OPEN
45
IFF, FEEDFORWARD CURRENT (A)
7.0
5.0
50
TJ, JUNCTION TEMPERATURE (°C)
ISS(D), SOFT START DISCHARGE CURRENT (mA)
ISS(C), SOFT START CHARGE CURRENT (A)
DCMAX, MAXIMUM DUTY CYCLE (%)
50
RIN(VEA), VEA INPUT RESISTANCE (k)
DCMAX, MAXIMUM DUTY CYCLE (%)
TYPICAL CHARACTERISTICS
−25
0
25
50
75
100
125
150
4.99
4.97
IREF = 0 mA
4.95
IREF = 6 mA
4.93
4.91
−50
−25
0
25
50
75
100
125
150
TJ, JUNCTION TEMPERATURE (°C)
TJ, JUNCTION TEMPERATURE (°C)
Figure 26. PWM Comparator Lower Input
Threshold versus Junction Temperature
Figure 27. Reference Voltage versus Junction
Temperature
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NCP1561
DETAILED OPERATING DESCRIPTION
The NCP1561 is a push−pull PWM controller for use in
48 V telecom power converters or 42 V automotive
systems. This controller contains all the features and
flexibility required in high density isolated dc−dc modules
and on−board designs for telecom and automotive systems.
It can be configured for operation in voltage−mode with
feedforward or current−mode control. The extensive set of
features included in the NCP1561 facilitates system design
and reduces overall system cost and component count by
incorporating supervisory functions and components
traditionally found outside the controller. Features of the
NCP1561 include a high voltage start−up regulator, fast line
feedforward, a line undervoltage lockout, dual mode
overcurrent protection, programmable maximum duty cycle
limit, programmable soft start and external voltage
reference.
Voltage−mode operation with line feedforward provides
better line regulation without some of the traditional
problems associated with current−mode control. The
controller is configured for voltage−mode operation by
routing the internal Feedforward Ramp output
(RAMP_OUT) to the PWM Comparator non−inverting
input (RAMP_IN). The amplitude of the Feedforward Ramp
varies inversely proportional to the input voltage. Operation
in current−mode control is obtained by routing a signal
proportional to the inductor current into the PWM
Comparator non−inverting input (VEA pin). In either mode,
the maximum duty cycle is inversely proportional to the line
voltage, as configured by the DCMAX pin and FF pins.
reaches approximately 10.3 V, the start−up regulator turns
OFF and the outputs are enabled. When VAUX reaches 7 V,
the outputs are disabled and the start−up regulator turns ON.
This mode of operation is known as Dynamic Self Supply
(DSS).
The start−up circuit sources current out of the VAUX pin.
It is recommended to place a diode between CAUX and the
auxiliary supply as shown in Figure 28. This will allow the
NCP1561 to charge CAUX while preventing the start−up
regulator from sourcing current into the auxiliary supply.
ISTART
Vin
ISTART
To auxiliary supply
VAUX
IAUX
CAUX
Isupply
Disable
Figure 28. Recommended VAUX Configuration
Power to the controller while operating in the self−bias or
DSS mode is provided by CAUX. Therefore, CAUX must be
sized such that a VAUX voltage greater than 7 V is
maintained while the outputs are enabled and the converter
reaches regulation. Also, the VAUX discharge time (from
10.3 V to 7 V) must be greater than the soft start charge
period to assure the converter turns ON. The start−up circuit
is rated at a maximum voltage of 150 V. If the device
operates in the DSS mode, power dissipation should be
controlled to avoid exceeding the maximum power
dissipation of the controller.
The start−up regulator is disabled by biasing VAUX above
7 V once the outputs are enabled. It can also be disabled by
biasing VAUX above VAUX(on) (typically 10.3 V). This
feature allows the NCP1561 to operate from an independent
12 V (±10%) supply. The independent supply should keep
VAUX above VAUX(on). Otherwise the Output Latch will not
be SET and the outputs will remain OFF after a fault
condition is cleared. If operating from an independent
supply, the Vin and VAUX pins should be connected together.
High Voltage Start−up Regulator
The NCP1561 contains an internal high voltage start−up
regulator that eliminates the need for external start−up
components. In addition, this regulator increases the
efficiency of the supply as it uses no power when in the
normal mode of operation, but instead uses power supplied
by an auxiliary winding. The start−up regulator consists of
a constant current source that supplies current from the input
line voltage (Vin) to the capacitor on the VAUX pin (CAUX).
The start−up current is typically 13.0 mA. Once VAUX
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NCP1561
Line Undervoltage Shutdown
The NCP1561 incorporates a line undervoltage shutdown
(UV) circuit. The undervoltage threshold is approximately
1.54 V.
The UV circuit can be biased using an external resistor
divider from the input line. The resistor divider must be
sized to enable the controller once Vin is within the required
operating range.
Once the UV condition is removed and VAUX reaches
VAUX(on), the controller initiates a soft start cycle, as shown
in Figure 29.
The UV pin can also be used to implement a remote
enable/disable function. Biasing the UV pin below its UV
threshold disables the converter.
SOFT START
VAUX(on)
VAUX
VAUX(off)
0V
2V
0V
2V
0V
UV Voltage
Soft Start Voltage
OUT2
0V
OUT1
0V
Figure 29. Soft Start Timing Diagram (Using Auxiliary Winding)
If the UV threshold is reached, once in normal operation,
the soft start capacitor is discharged, and the outputs are
immediately disabled as shown in Figure 30. Also, if an UV
condition is detected, the 5.0 V Reference Supply is
disabled.
VAUX(on)
VAUX
VAUX(off)
0V
UV Fault
UV Voltage
VUV
0V
Propagation Delay
to Outputs (tUV)
OUT1
0V
OUT2
0V
Figure 30. UV Fault Timing Diagram
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NCP1561
Feedforward Ramp Generator
The NCP1561 incorporates line feedforward (FF) to
compensate for changes in line voltage. A FF Ramp
proportional to Vin is generated and compared to the error
signal. If the line voltage changes, the FF Ramp slope
changes accordingly. The duty cycle will be adjusted
immediately instead of waiting for the line voltage change
to propagate around the system and be reflected back on
VEA.
A resistor between Vin and the FF pin (RFF) sets the
feedforward current (IFF). The FF Ramp is generated by
charging an internal 10.8 pF capacitor (CFF) with a constant
current proportional to IFF. The FF Ramp is finished
(capacitor is discharged) once the Oscillator Ramp reaches
2.0 V. Please refer to Figure 3 for a functional drawing of the
Feedforward Ramp generator.
IFF is usually a few hundred microamps, depending on the
operating frequency and the required duty cycle. If the
operating frequency and maximum duty cycle are known,
IFF is calculated using the equation below:
IFF For example, if a system is designed to operate at an
oscillator frequency of 150 kHz, with a 45% maximum duty
cycle at 36 V, the DCMAX pin can be grounded and IFF is
calculated as follows:
1
T1
6.66 s
150 kHz
f
ton(max) DCMAX T 0.45 6.66 s 3.0 s
IFF CFF VDC(inv) 125 k
6.7 k ton(max)
10.8 pF 1.0 V 125 k
67.2 A
6.7 k 3.0 s
As the minimum line voltage is 36 V, the required
feedforward resistor is calculated using the equation below:
V
RFF in 12.0 k 36 V 12.0 k 523 k
IFF
67.2 A
From the above calculations it can be observed that IFF is
controlled predominantly by the value of RFF, as the
resistance seen into the FF pin is only 12 k. If a tight
maximum duty cycle control over temperature is required,
RFF should have a low thermal coefficient. If current−mode
control is used and the FF Ramp generator is not used for
maximum duty cycle control, the FF Ramp generator can be
disabled grounding the FF pin.
CFF VDC(inv) 125 k
6.7 k ton(max)
where VDC(inv) is the voltage on the inverting input of the
Max DC Comparator and ton(max) is the maximum ON time.
Figure 22 shows the relationship between IFF and DCMAX.
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NCP1561
Current Limit
The NCP1561 has two overcurrent protection modes,
cycle by cycle and cycle skip. It allows the NCP1561 to
handle momentary and hard shorts differently for the best
tradeoff in system performance and safety. The outputs are
disabled typically 86 ns after a current limit fault is detected.
The cycle by cycle mode terminates the conduction cycle
(reducing the duty cycle) if the voltage on the CS pin
exceeds 0.95 V. The cycle skip mode is enabled if the voltage
on the CS pin reaches 1.15 V. Once a cycle skip fault is
detected, the outputs are disabled, the soft start and cycle
skip capacitors are discharged, and the cycle skip period
(TCSKIP) commences.
NORMAL
OPERATION
ILIM
Faults
The cycle skip period is set by an external capacitor
(CCSKIP). Once a cycle skip fault is detected, the cycle skip
capacitor is discharged followed by a charge cycle. The
charge current is 12.3 A. The cycle skip period ends when
the voltage on the cycle skip capacitor reaches 2.0 V. If the
cycle skip period is known, the cycle skip capacitor is
calculated using the equation below:
CCSKIP TCSKIP 12.3 A
2V
Using the above equation, a cycle skip period of 11.0 s
requires a cycle skip capacitor of 68 pF. The differences
between the cycle by cycle and cycle skip modes are shown
in Figure 31.
RESET
SOFT START
VAUX(on)
VAUX
VAUX(off)
0V
OUT1
0V
OUT2
0V
ILIM2
ILIM1
CS Voltage
0V
TCSKIP
Cycle Skip Voltage
2V
0V
Figure 31. Overcurrent Faults Timing Diagram
Once the cycle skip period is complete and VAUX reaches
VAUX(on), a soft start sequence commences. The possible
minimum OFF time is set by CCSKIP. The actual OFF time
is generally greater than the cycle skip period if operating in
DSS because it is the cycle skip period added to the time it
takes VAUX to cycle between VAUX(off) and VAUX(on). If
operating from an independent supply, the OFF time is the
cycle skip period.
The voltage on the RT pin is laser trim adjusted during
manufacturing to 1.3 V for an RT of 101 k. A current set
by RT generates an Oscillator Ramp by charging an internal
10 pF capacitor as shown in Figure 3. The period ends
(capacitor is discharged) once the Oscillator Ramp reaches
2.0 V. If RT increases, the current and the Oscillator Ramp
slope decrease, thus reducing the frequency. If RT decreases,
the opposite effect is obtained. Figure 17 shows the
relationship between RT and the oscillator frequency.
Oscillator
The NCP1561 oscillator frequency is set by a single
external resistor connected between the RT pin and GND.
The oscillator is designed to operate up to 250 kHz.
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NCP1561
5.0 V Reference
The NCP1561 includes a precision 5.0 V reference output.
The reference output is biased directly from VAUX and it can
supply up to 6 mA. Load regulation is 50 mV and line
regulation is 100 mV within the specified operating range.
It is recommended to bypass the reference output with a
0.1 F ceramic capacitor. The reference output is disabled
when an UV fault is present.
Maximum Duty Cycle
A dedicated internal comparator limits the maximum ON
time by comparing the FF Ramp to VDC(inv) as shown in
Figure 3. If the FF Ramp voltage exceeds VDC(inv), the
output of the Max DC Comparator goes high. This will reset
the Output Latch, thus turning OFF the outputs and limiting
the duty cycle.
Duty cycle is defined as:
t
DC on ton f
T
PWM Comparator
In steady state operation, the PWM Comparator adjusts
the duty cycle by comparing the error signal to the FF Ramp
(voltage−mode) or a ramp proportional to the inductor
current (current−mode). The error signal is fed into the VEA
input. The FF Ramp or the inductor ramp is fed into the
RAMP_IN pin. If operating in voltage−mode, the
connection between the RAMP_OUT and RAMP_IN pins
should be as close as possible to minimize parasitic
inductance. It can be easily routed underneath the package.
The VEA input can be driven directly with an optocoupler
and a pull up resistor (REA) from VREF as shown in Figure
33. The drive of the control pin is simplified by internally
incorporating a series diode and resistor. The series diode
provides a 0.7 V offset between the VEA input and the PWM
Comparator inverting input. The outputs are enabled if the
VEA voltage is approximately 0.7 V above the valley voltage
of the ramp (Vvalley) in the RAMP_IN pin.
Therefore, the maximum ON time can be set to yield the
desired DC if the operating frequency is known. The
maximum ON time is set by adjusting the FF Ramp to reach
VDC(inv) in a time equal to ton(max) as shown in Figure 32.
The maximum ON time should be set for the minimum line
voltage. As line voltage increases, the slope of the FF Ramp
increases. This reduces the duty cycle below DCMAX, which
is a desirable feature as the duty cycle is inversely
proportional to line voltage.
Oscillator Ramp
2V
0V
T
FF Ramp
VREF
VDC(inv)
11
0V
REA
ton(max)
PWM
Comparator
−
+
Figure 32. Maximum ON Time Limit Waveforms
An internal resistor divider from a 2.0 V reference is used
to set VDC(inv). If the DCMAX pin is grounded, VDC(inv) is
1.0 V. If the pin is floating, VDC(inv) is 1.4 V. This is
equivalent to 71% (36% DC) or 100% (50% DC) of a FF
Ramp, with a peak voltage of 1.4 V. VDC(inv) can be adjusted
to other values by placing an external resistor network on the
DCMAX pin. For example, if the minimum line voltage is 36
V, RFF is 432 k, oscillator frequency is 150 kHz and a
maximum duty cycle of 45% is required, VDC(inv) is
calculated as follows:
VDC(inv) VDC(inv) 2 k
VEA
+
10
Feedback
Signal
20 k VEA
−
Vpeak
RAMP_IN
12 Vvalley
0V
FF Ramp
or
Inductor Ramp
Figure 33. Optocoupler driving VEA input
IFF 6.7 k ton(max)
CFF 125 k
The pull−up resistor is selected such that in the absence of
the error signal, the voltage on the VEA pin exceeds the peak
amplitude of the ramp in the RAMP_IN pin. Otherwise, the
converter may not be able to reach maximum duty cycle. If
operating in voltage−mode, REA is calculated using the
equation below:
81.0 A 6.7 k 3.0 s
1.2 V
10.8 pF 125 k
This can be achieved by connecting a 23.44 k resistor
from the DCMAX pin to GND. The maximum duty cycle
limit can be disabled connecting a 100 k resistor between
the DCMAX and VREF pins.
REA 22 k
VREF 0.7 V
1
0.0515I
Vvalley C fFF
FF
where, CFF is the internal FF capacitor, typically 10.8 pF.
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NCP1561
Control Outputs
The NCP1561 has two off−phase control outputs, OUT1
and OUT2. Figure 35 shows the relationship between OUT1
and OUT2.
Soft Start
Soft start (SS) allows the converter to gradually reach
steady state operation, thus reducing start−up stress and
surges on the system. The duty cycle is limited during a soft
start sequence by comparing the Oscillator Ramp to the SS
voltage (VSS) by means of the Soft Start Comparator.
Once faults are removed and VAUX reaches VAUX(on), a
6.2 A current source starts to charge the capacitor on the SS
pin. The Soft Start Comparator controls the duty cycle while
the SS voltage is below 2.0 V. Once VSS reaches 2.0 V, it
exceeds the Oscillator Ramp voltage and the Soft Start
Comparator does not limit the duty cycle. Figure 34 shows
the relationship between the outputs duty cycle and the soft
start voltage.
Oscillator
Ramp
OUT1
OUT2
Figure 35. Control Outputs Timing Diagram
Once VAUX reaches VAUX(on), the internal start−up circuit
is disabled and the One Shot Pulse Generator is enabled. If
no faults are present, the outputs turn ON. Otherwise, the
outputs remain OFF until the fault is removed and VAUX
reaches VAUX(on) again.
The control outputs are biased from VAUX. The outputs
can supply up to 10 mA each and their high state voltage is
usually 0.2 V below VAUX. Therefore, the auxiliary supply
voltage should not exceed the maximum input voltage of the
driver stage.
If the control outputs need to drive a large capacitive load,
a driver should be used between the NCP1561 and the load.
Figures 19 and 20 show the relationship between the
output’s rise and fall times vs capacitive load.
VSS
OUT1
OUT2
Figure 34. Soft Start Timing Diagram
Thermal Protection
Internal Thermal Shutdown Circuitry is provided to
protect the integrated circuit in the event the maximum
junction temperature is exceeded. When activated, typically
at 180C, the controller is forced into a low power reset
state, discharging the soft start capacitor and disabling the
output drivers and the bias regulator. Once the junction
temperature falls below 163C, the NCP1561 enters a soft
start mode and it is allowed to resume normal operation.
This feature is provided to prevent catastrophic failures from
accidental device overheating.
If the soft start period is too long, VAUX may discharge to
7 V before the converter output is completely in regulation
causing the outputs to be disabled. If the converter output is
not completely discharged when the outputs are re−enabled,
the converter will eventually reach regulation exhibiting a
non−monotonic start−up behavior. But, if the converter
output is completely discharged when the outputs are
re−enabled, the cycle may repeat and the converter will not
start.
In the event of an UV or cycle skip fault, the soft start
capacitor is discharged. Once the fault is removed, a soft
start cycle commences. The soft start steady state voltage is
approximately 4.1 V.
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NCP1561
PACKAGE DIMENSIONS
SO−16
D SUFFIX
CASE 751B−05
ISSUE J
−A−
16
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSIONS A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
9
−B−
1
P
8 PL
0.25 (0.010)
8
M
B
S
G
R
K
F
X 45 C
−T−
SEATING
PLANE
J
M
D
16 PL
0.25 (0.010)
M
T B
S
A
S
DIM
A
B
C
D
F
G
J
K
M
P
R
MILLIMETERS
MIN
MAX
9.80
10.00
3.80
4.00
1.35
1.75
0.35
0.49
0.40
1.25
1.27 BSC
0.19
0.25
0.10
0.25
0
7
5.80
6.20
0.25
0.50
INCHES
MIN
MAX
0.386
0.393
0.150
0.157
0.054
0.068
0.014
0.019
0.016
0.049
0.050 BSC
0.008
0.009
0.004
0.009
0
7
0.229
0.244
0.010
0.019
The product described herein (NCP1561) may be covered by one or more U.S. patents. There may be other patents pending.
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 may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
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For additional information, please contact your
local Sales Representative.
NCP1561/D