NCP3155A, NCP3155B
3 A Synchronous Buck
Regulator
The NCP3155 is a DC/DC synchronous switching regulator with
fully integrated power switches and full fault protection. The
switching frequency of 1 MHz and 500 kHz allows the use of small
filter components, which results in smaller board space and reduced
BOM cost. Available in a SOIC-8 package.
Features
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SOIC−8 NB
CASE 751
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Input Voltage Range from 4.7 V to 24 V
Adjustable Output Voltage
1 MHz Operation (NCP3155A – 500 kHz)
Internally Programmed 1.2 ms Soft−Start (NCP3155A – 2.4 ms)
0.8
±
1.0% Reference Voltage
48 mW HS−FET and 18 mW LS−FET
Current Limit Protection
Transconductance Amplifier with External Compensation
Input Undervoltage Lockout
Output Overvoltage and Undervoltage Detection
These are Pb−Free Devices
Set Top Boxes
DVD Drives and HDD
LCD Monitors and TVs
Cable Modems
Telecom/Networking/Datacom Equipment
MARKING DIAGRAM
8
3155x
ALYW
G
1
3155x
A
L
Y
W
G
= Specific Device Code
x = A or B
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
Typical Applications
PIN CONNECTIONS
PGND
V
IN
V
OUT
BST
COMP
(Top View)
V
SW
ISET
AGND
FB
4.7 V
−
24 V
V
IN
BST VSW
PGND
NCP3155
ISET
COMP
FB1
AGND
ORDERING INFORMATION
Device
NCP3155ADR2G
NCP3155BDR2G
Package
Shipping
†
SOIC−8 2500 / Tape & Reel
(Pb−Free)
SOIC−8 2500 / Tape & Reel
(Pb−Free)
Figure 1. Typical Application Circuit
†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.
©
Semiconductor Components Industries, LLC, 2011
February, 2011
−
Rev. 1
1
Publication Order Number:
NCP3155/D
NCP3155A, NCP3155B
BST
VIN
VIN
INTERNAL BIAS
POR/STARTUP
THERMAL SD
VC
ACTIVE
BOOST
OSCILLATOR
CLK/
DMAX/
SOFT
START
RAMP
1.5 V
+
−
GATE
DRIVE
LOGIC
LEVEL
SHIFT
VIN
CURRENT
LIMIT
ISET
VC
HSDRV
VSW
SAMPLE &
HOLD
COMP
REF
LSDRV
PGND
FB
+
−
+
−
ISET
OOV
OUV
AGND
Figure 2. NCP3155 Block Diagram
PIN FUNCTION DESCRIPTION
Pin
1
2
Pin Name
PGND
V
IN
Description
The PGND pin is the high current ground pin for the lower MOSFET and drivers which should be soldered to a
large copper area to reduce thermal resistance.
The V
IN
pin powers the internal control circuitry and is monitored by an undervoltage comparator. The V
IN
pin
is also connected to the internal power NMOS switch. It is also used in conjunction with the V
SW
pin to sense
current in the high side MOSFET. The V
IN
pin has high dI/dt edges and must be decoupled to PGND pin close
to the pin of the device.
Supply rail for the floating top gate driver. Connect a capacitor (CBST) between this pin and the V
SW
pin. Typ-
ical values for CBST range from 1 nF to 10 nF.
Compensation pin. The comp pin is the output of the transconductance amplifier and the non−inverting input of
the PWM comparator. The comp pin in conjunction with the FB pin are used to compensate the voltage−control
feedback loop.
Inverting input to the Operational Transconductance Amplifier (OTA). The FB pin in conjunction with the extern-
al compensation serves to stabilize and achieve the desired output voltage with voltage mode compensation.
The AGND pin serves as small−signal ground. All small−signal ground paths should connect to the AGND pin
at a single point to avoid any high current ground returns.
Bottom gate MOSFET driver pin and the internal current set pin. Place a resistor to ground to set the current
limit of the converter.
The V
SW
pin is the connection of the drain and source of the internal N MOSFETS. The V
SW
pin swings from
V
IN
when the high side switch is on to small negative voltages when the low side switch is on with high dV/dt
transitions.
3
4
BST
COMP
5
6
7
8
FB
AGND
ISET
V
SW
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NCP3155A, NCP3155B
ABSOLUTE MAXIMUM RATINGS
(measured vs. GND pin 8, unless otherwise noted)
Rating
Main Supply Voltage Input
Boost to V
SW
differential voltage
High Side Drive Boost Pin
Switch Voltage Node
Transconductance Amplifier Output
Feedback
Current Limit Set
Operating Junction Temperature Range (Note 1)
Maximum Junction Temperature
Storage Temperature Range
Thermal Characteristics
−
SOIC−8 Package
Thermal Resistance Junction−to−Air
Lead Temperature Soldering (10 sec):
Reflow (SMD styles only) Pb−Free (Note 3)
(Note 2)
(Note 3)
Symbol
V
CC
BST−V
SW
BST
V
SW
COMP
FB
ISET
T
J
T
J(MAX)
T
stg
R
qJA
R
F
V
MAX
26.4
13.2
45
30
5.5
6.0
13.2
V
MIN
−0.3
−0.3
−0.3
−0.6
−0.3
−0.3
−0.3
Unit
V
V
V
V
V
V
V
°C
°C
°C
°C/W
°C
−40
to +125
+150
−55
to +150
110
170
260 Peak
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
1. The maximum package power dissipation limit must not be exceeded.
P
D
+
T
J(max)
*
T
A
R
qJA
2. The value of
q
JA
is measured with the device mounted on 1 in
2
FR*4 board with 1 oz. copper, in a still air environment with T
A
= 25°C. The
value in any given application depends on the user’s specific board design.
3. The value of
q
JA
is measured with the device mounted on minimum footprint, in a still air environment with T
A
= 25°C. The value in any given
application depends on the user’s specific board design.
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NCP3155A, NCP3155B
ELECTRICAL CHARACTERISTICS
(
−40°C
< T
J
< +125°C, V
CC
= 12 V, for min/max values unless otherwise noted)
Characteristic
Input Voltage Range
SUPPLY CURRENT
V
CC
Supply Current
V
CC
Supply Current
NCP3155A
NCP3155B
V
FB
= 0.8 V, Switching, V
CC
= 4.7 V
V
FB
= 0.8 V, Switching, V
CC
= 24 V
V
FB
= 0.8 V, Switching, V
CC
= 4.7 V
V
FB
= 0.8 V, Switching, V
CC
= 24 V
UNDER VOLTAGE LOCKOUT
UVLO Rising Threshold
UVLO Falling Threshold
OSCILLATOR
Oscillator Frequency
Oscillator Frequency
Ramp−Amplitude Voltage
Ramp Valley Voltage
PWM
Minimum Duty Cycle
Maximum Duty Cycle
Soft Start Ramp Time
NCP3155A
NCP3155B
V
FB
= V
COMP
(Note 4)
−
80
−
−
0.9
(Notes 4 and 6)
V
FB
= 750 mV
V
FB
= 850 mV
TJ = 25 C
4.7 V < V
IN
< 28 V,
−40°C
< T
J
< +125°C
V
FB
= 750 mV
V
FB
= 850 mV
−
45
45
−
0.792
0.784
4.0
−
0.91
0.56
V
IN
= 12 V
V
IN
= 4.7 V
V
IN
= 12 V
V
IN
= 4.7 V
−
−
−
−
7
R
SET
= 22.1 kW
(Notes 4 and 7)
(Notes 4 and 7)
−
−
−
7.0
84
2.4
1.2
1.3
70
70
70
0.5
0.8
0.8
4.4
72
1.00
0.60
48
65
18
21
13.5
298
175
20
−
−
−
−
1.9
−
100
100
500
0.808
0.816
5.0
250
1.09
0.64
63
85
35
50
18
−
−
−
%
%
ms
NCP3155A
NCP3155B
T
J
= +25°C, 4.7 V
v
V
CC
v
28 V
T
J
=
−40°C
to +125°C, 4.7 V
v
V
CC
v
28 V
T
J
= +25°C, 4.7 V
v
V
CC
v
28 V
T
J
=
−40°C
to +125°C, 4.7 V
v
V
CC
v
28 V
V
peak
−
V
alley
415
400
830
820
−
0.46
500
500
1000
1000
1.5
0.71
585
600
1170
1180
−
0.85
kHz
kHz
kHz
kHz
V
V
V
CC
Rising Edge
V
CC
Falling Edge
4.0
3.5
4.3
3.9
4.7
4.3
V
V
−
−
−
−
11.1
31.5
16.5
54.7
−
−
−
−
mA
mA
mA
mA
Conditions
−
Min
4.7
Typ
Max
24
Unit
V
ERROR AMPLIFIER (GM)
Transconductance
Open Loop dc Gain
Output Source Current
Output Sink Current
FB Input Bias Current
Feedback Voltage
COMP High Voltage
COMP Low Voltage
OUTPUT VOLTAGE FAULTS
Feedback OOV Threshold
Feedback OUV Threshold
PWM OUTPUT STAGE
High−Side Switch On Resistance
Low−Side Switch On Resistance
OVERCURRENT
ISET Source Current
Current Limit Set Voltage (Note 5)
THERMAL SHUTDOWN
Thermal Shutdown
Hysteresis
4.
5.
6.
7.
°C
°C
mA
mV
mW
mW
V
V
mS
dB
mA
mA
nA
V
V
V
mV
Guaranteed by design.
The voltage sensed across the high side MOSFET during conduction.
This assumes 100 pF capacitance to ground on the COMP Pin and a typical internal R
o
of > 10 MW.
This is not a protection feature.
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NCP3155A, NCP3155B
TYPICAL PERFORMANCE CHARACTERISTICS
100
90
80
EFFICENCY (%)
70
60
50
40
30
20
10
0
0
0.5
NCP3155A, V
in
= 12 V
Typical Application Circuit
Figure 45
1
1.5
2
I
out
, OUTPUT CURRENT (A)
2.5
3
1.5 V
100
90
80
EFFICENCY (%)
1.2 V
70
60
50
40
30
20
10
0
0
0.5
NCP3155B, V
in
= 12 V
Typical Application Circuit
Figure 45
1
1.5
2
I
out
, OUTPUT CURRENT (A)
2.5
3
1.5 V
V
out
= 5.0 V
3.3 V
1.2 V
V
out
= 5.0 V
3.3 V
Figure 3. Efficiency vs Output Current and
Output Voltage
Figure 4. Efficiency vs Output Current and
Output Voltage
100
90
80
EFFICENCY (%)
70
60
50
40
30
20
10
0
0
V
in
= 12 V
V
in
= 24 V
V
OUT
(V)
V
in
= 18 V
5.1
5.08
5.06
5.04
5.02
5
4.98
4.96
4.94
4.92
3
4.9 0
NCP3155A, V
out
= 5 V
Typical Application Circuit
Figure 45
0.4
0.8
1.2
1.6
V
in
= 18 V
V
in
= 12 V
V
in
= 24 V
NCP3155A, V
out
= 5 V
Typical Application Circuit
Figure 45
0.5
1
1.5
2
I
out
, OUTPUT CURRENT (A)
2.5
2.0
2.4
2.8
I
out
, OUTPUT CURRENT (A)
Figure 5. Efficiency vs Output Current and Input
Voltage
Figure 6. Load Regulation vs Input Voltage
Input = 12 V, Output = 5.0 V, Load = 2 A,
CH3 (Purple) = V
IN
, (CH2) Green = V
OUT
, CH1 (Yellow) = VSW
CH3: 200 mVac/div; CH2: 50 mVac/div; CH1: 5.0 V/div
Time Scale: 2.0
ms/div;
Figure 45
Input = 18 V, Output = 5.0 V, Load = 2 A,
CH3 (Purple) = V
IN
, (CH2) Green = V
OUT
, CH1 (Yellow) = VSW
CH3: 200 mVac/div; CH2: 50 mVac/div; CH1: 5.0 V/div
Time Scale: 2.0
ms/div;
Figure 45
Figure 7. Switching Waveforms (NCP3155A)
Figure 8. Switching Waveforms (NCP3155A)
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