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 startup 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.
Features
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MARKING
DIAGRAM
16
SO−16
D SUFFIX
CASE 751B
1
1
NCP1561 = Device Code
A
= Assembly Location
WL
= Wafer Lot
Y
= Year
WW
= Work Week
NCP1561
AWLYWW
16
•
•
•
•
•
•
•
•
•
•
•
•
Internal High Voltage Startup 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
V
in
UV
RAMP_OUT
FF
CS
CSKIP
R
T
DC
MAX
V
AUX
OUT1
GND
OUT2
RAMP_IN
V
REF
V
EA
SS
Typical Applications
•
48 V Telecommunication Power Converters
•
Industrial Power Converters
•
42 V Automotive Systems
M4
C1
C2
M2
OUT1
M3
High Side
Driver
Driver
M1
OUT2
Opto
TX1
ORDERING INFORMATION
Device
NCP1561DR2
Package
SO−16
Shipping
†
2500 Units/Reel
Vin
+
−
Startup
†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.
Lout
Cout
Feedforward
NCP1561
OUT2
OUT1
Error
Amplifier
Figure 1. Half−Bridge Block Diagram
©
Semiconductor Components Industries, LLC, 2004
1
August, 2004 − Rev. 3
Publication Order Number
NCP1561/D
NCP1561
V
in
High Voltage
Startup
Regulator
5.0 V
Reference
Thermal
Shutdown
V
AUX
V
REF
UV
CS
UV
Fault
Detection
Modulator
Output
Stage
OUT1
OUT2
CSKIP
R
T
Oscillator
FF
V
EA
SS
GND
DC
MAX
RAMP_OUT
RAMP_IN
Figure 2. Simplified Block Diagram
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2
NCP1561
V
AUX
Vin
1
Disable
I
AUX
V
AUX(on)
−
+
5.0 V Reference
DIS
Disable_V
REF
One Shot
Pulse
(250 ns)
+
−
Thermal
Shutdown
+
−
V
REF
15
CSKIP
6
C
CSKIP
One Shot
Pulse
(600 ns)
5
CS
+
−
+
1.2 V
−
+
−
Softstart
Comparator
Max DC
Comparator
−
+
Oscillator Ramp
+
V
DC(inv)
−
STOP
10 pF
7
R
T
R
T
+
1.3 V*
−
* Trimmed during
manufacturing to obtain
1.3 V with R
T
= 101 kW
+
−
2V
+
−
+
2V
−
38 kW
12
mA
Disable
−
+
−
+
+
2V
−
Clock
Q
Dominant
Reset
Latch
R
S
TF/F Q
V
AUX
13
Q
OUT1
−
+
1.52 V
V
AUX
V
AUX(on)
/V
AUX(off)
Output Latch
S
Dominant
Reset Q
Latch
R
STOP
Enable_ss
V
REF
11
16
V
AUX
C
AUX
V
in
2
UV
OUT2
V
REF
PWM
Comparator
−
+
10
2 kW
20 kW
12
RAMP_IN
2V
29 kW
29 kW
8
DC
MAX
R
P
V
REF
R
MDP
− +
V
EA
R
EA
+
1.0 V
−
V
REF
CURRENT MIRROR
6
mA
9
SS
C
SS
Enable_ss
I
1
I
1
2
2V
V
in
R
FF
I
+
+
+
V
−
−
10.8 pF
Clock
V
125 kW
One Shot
Pulse
FF Ramp
(Adjustable)
3
Buffer
RAMP_OUT
4
FF
I
FF
5.3 kW
6.7 kW
C
FF
Figure 3. NCP1561 Block Diagram
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NCP1561
PIN DESCRIPTION
Pin
1
Name
V
in
Application Information
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 V
AUX
pin. The charge current is typically 13.0 mA. Input voltage
range is 21.5 V to 150 V.
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.
Internal Feedforward (FF) Ramp Output. This signal can be externally routed to the RAMP_IN pin for
voltage−mode control operation.
An external resistor between V
in
and this pin adjusts the amplitude of the FF Ramp inversely proportional to
V
in
. By varying the Feedforward Ramp amplitude in proportion to the input voltage, changes in loop
bandwidth resulting from V
in
changes are eliminated.
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.
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
mA.
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.
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.
An internal 6.0
mA
current source charges the external capacitor connected to this pin. The duty cycle is
limited during startup 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.
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.
Precision 5.0 V reference output. Maximum output current is 6.0 mA.
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 V
EA
pin.
Output 2.
Control circuit ground.
Output 1.
Positive input supply voltage. This pin is connected to an external capacitor for energy storage. An internal
current source supplies current from V
in
to this pin. Once the voltage on V
AUX
reaches approximately 10.3 V,
the current source turns OFF. It turns ON again once V
AUX
falls to 7 V. During normal operation, power is
supplied to the IC via this pin, by means of an auxiliary winding. The startup circuit is disabled if the voltage
on the V
AUX
pin exceeds 10.3 V.
2
3
4
UV
RAMP_OUT
FF
5
6
CS
CSKIP
7
8
R
T
DC
MAX
9
SS
10
V
EA
11
12
V
REF
RAMP_IN
13
14
15
16
OUT2
GND
OUT1
V
AUX
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4
NCP1561
MAXIMUM RATINGS
(Note 1)
Rating
Input Line Voltage
Auxiliary Supply Voltage
Auxiliary Supply Input Current
OUT1 and OUT2 Voltage
OUT1 and OUT2 Output Current
5.0 V Reference Voltage
5.0 V Reference Output Current
All Other Inputs/Outputs Voltage
All Other Inputs/Outputs Current
Operating Junction Temperature
Storage Temperature Range
Power Dissipation at T
A
= 25°C
Thermal Resistance, Junction−to−Ambient
Symbol
V
in
V
AUX
I
AUX
V
OUT
I
OUT
V
REF
I
REF
V
IO
I
IO
T
J
T
stg
P
D
R
θJA
Value
−0.3 to 150
−0.3 to 16
35
−0.3 to (V
AUX
+ 0.3 V)
10
−0.3 to 6.0
6.0
−0.3 to V
REF
10
−40 to 150
−55 to 150
0.77
130
Unit
V
V
mA
V
mA
V
mA
V
mA
_C
_C
W
_C/W
1. Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit
values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not
implied, damage may occur and reliability may be affected.
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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