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OCP2576
Simple Switch 3A Step-down Voltage Regulator
„ Features
„ General Description
z Output voltage: 3.3V, 5V, 12V, 15V and adjustable The OCP2576 series of regulators are monolithic IC
output versions
that provide all the active function for a step-down
z Adjustable version output voltage range:1.23V to (buck) switching regulator, capable of driving 3A load
30V±4% max over line and load conditions
with excellent line and load regulation. These
z Guaranteed 3A output current
devices are available in fixed output voltages of
z Input voltage up to 36V
3.3V, 5V, 12V, 15V and an adjustable output version.
z
z
z
z
z
Requires only 4 external components
52KHz fixed frequency internal oscillator
TTL shutdown capability, low power standby mode
High efficiency
Thermal shutdown and current limit protection
Requiring a minimum number of external
components, these regulators are simple to use and
include internal frequency compensation and a fixed
frequency oscillator.
A standard series of inductors optimized for use with
„ Applications
z Simple High-efficiency step-down regulator
z Efficient pre-regulator for linear regulators
z Positive to negative converter(Buck-Boost)
the OCP2576 are available from several different
manufacturers. This feature greatly simplifiers the
design of switch-mode power supplies.
Others features include a guaranteed ±4% tolerance
on output within specified input voltages and output
load conditions, and ±10% on the oscillator
frequency. External shutdown in included, featuring
50μA (typical) standby current. The output switch
includes cycle-by-cycle current limiting, as well as
thermal shutdown for full protection under fault
conditions.
„ Pin Configuration
(1) TO220-5L
(Top View)
Metal Tab Gnd
5 SD
4 FB
3 GND
2 OUTPUT
1 VIN
Symbol
1
2
3
4
5
Name
Vin
Output
Gnd
FB
SD
Descriptions
Operating Voltage Input
Switching Output
Ground
Output Voltage Feedback Control
ON/OFF Shutdown
(2) TO263-5L
(Top View)
5 SD
4 FB
3 GND
2 OUTPUT
1 VIN
Metal Tab Gnd
Page1-9
Rev. 1.3 Mar. 02, 2006

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OCP2576
Simple Switch 3A Step-down Voltage Regulator
„ Block Diagram
UNREGULATED
DC INPUT
VIN
FEED-
CIN + BACK
1
4
INTERNAL
REGULATOR
R2
R1
1.0K
FIXED GAIN
ERROR AMP
+
-
COMPARATOR
+
-
1.23V
BAND-GAP
REFERANCE
52KHz
OSCILLATOR
RESET
ON/OFF
3 AMP
SWITCH
DRIVER
THERMAL
SHUTDOWN
CURRENT
LIMIT
ON/OFF
5
OUTPUT
2
L1
VOUT
GND D1
+
3 COUT
3.3V: R2=1.7K 5V: R2=3.1K 12V: R2=8.4K
15V: R2=11.3K For Adjustable R2=0KR1=open
„ Pin Functions
VIN
This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at
this pin to minimize voltage transients and to supply the switching currents needed by the regulator.
Ground
Circuit ground.
Output
Internal switch, the voltage at this pin switches between (VIN – VSAT) and approximately – 0.5V.To minimize
coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept to a minimum.
Feedback
Senses the regulated output voltage to complete the feedback loop.
ON/OFF
Allows the switching regulator circuit to be shut down using logic level signals. Pulling this pin below a threshold
voltage of approximately 1.5V turns the regulator on, and pulling this pin above 1.51V (up to a maximum of 25V)
shuts the regulator down. If this shutdown feature is not needed, the ON/OFF pin can be wired to the ground pin
or it can be left open, in either case the regulator will be in the ON condition.
Page2-9
Rev. 1.3 Mar. 02, 2006

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OCP2576
Simple Switch 3A Step-down Voltage Regulator
„ Absolute Maximum Ratings (Note1)
Parameter
Maximum Supply Voltage
ON/OFF Pin Input Voltage
Output Voltage to Ground Steady State
Power Disipation
Storage Temperature Range
ESD Susceptibility (Human Body Model)
Maximum Junction Temperature
Conditions
Temperature Range
Supply Voltage
Rating
45
-0.3~+VIN
-1
Internally limited
-65~150
2
150
-40~125
4.5~40
Unit
V
V
V
KV
V
„ Electrical Characteristics (All Output Voltaeg Versions)
Unless otherwise specified, VIN=12V for the 3.3V, 5V, and adjustable version , VIN=25V for the 12V version, and
VIN=30V for the 15V version, ILOAD=0.5A
Symbol
Ib
fO
Paramrter
Feedback bias current
Oscillator frequency
Conditions
VOUT=5V
(Adjustable version only)
(Note 11)
Min.
(Note2)
47
Typ.
50
52
Max.
(Note2)
100
Unit
nA
58 KHz
VSAT
Saturation voltage
IOUT=3A (Note 4)
1.5 2.0 V
DC Max.Duty Cycle(ON)
(Note 5)
93 98
%
ICL
IL
IQ
ISTBY
VIL
VIH
IH
IL
θJA
θJA
θJC
θJA
Current limit
(Notes 4,11)
Output leakage current
Quiescent Current
Standby Quiesient Current
Output=0V (Notes 6,7)
Output=-1V (Note 10)
(Note 6)
ON/OFF Pin=5V (OFF)
ON/OFF pin logic input level
ON/OFF pin input current
Thermal Resistence
VOUT=Nominal Output Voltage
VOUT=0V
ON/OFF Pin=5V (OFF)
ON/OFF Pin=0V (ON)
T Pakage, Junction to Ambient
(Note8)
T Pakage, Junction to Ambient
(Note9)
T Pakage, Junction to Case
K Pakage, Junction to Ambient
(Note10)
5.5
1.38
6.12
7.5
6
200
1.36
1.50
12
0
65
45
2
50
6.7 A
2.0 mA
3.0 mA
12 mA
300 µA
1.43
V
30
10
µA
/W
/W
/W
/W
Page3-9
Rev. 1.3 Mar. 02, 2006

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OCP2576
Simple Switch 3A Step-down Voltage Regulator
„ Electrical Characteristics (Continued)
Specifications with standard type face are for TJ=25, System Parameters (Note 3)
Symbol
OCP2576-ADJ
OCP2576-3.3V
OCP2576-5V
OCP2576-12V
OCP2576-15V
VFB
η
VOUT
η
VOUT
η
VOUT
η
VOUT
η
Parameter
Feedback
Voltage
Efficiency
Output voltage
Efficiency
Output voltage
Efficiency
Output voltage
Efficiency
Output voltage
Efficiency
Conditions
8VVIN36V
0.5AILOAD3A
VOUT=5V
VIN =12V,
ILOAD =3A ,VOUT=5V
6VVIN36V
0.5AILOAD3A
VIN =12V, ILOAD =3A
8VVIN36V
0.5AILOAD3A
VIN =12V, ILOAD =3A
15VVIN36V
0.5AILOAD3A
VIN =15V, ILOAD =3A
18VVIN36V
0.5AILOAD3A
VIN =18V, ILOAD =3A
Min.
(Note 2)
1.193
Typ.
1.230
Max.
(Note 2)
1.267
Unit
V
77 %
3.168 3.3 3.432
V
75 %
4.800
5.0
5.20
V
77 %
11.520 12 12.480 V
88 %
14.400 15 15.600 V
88 %
Note 1: Absolute Maximum Ratings indicates limits beyound which damage to the device may occur. Operating
Ratings indicate conditions for which the device is intended to be functional, but specific performance is not
guaranteed. For guarabted spcifications and the best conditions, see the Electrical Characteristics.
Note 2: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face).
All room temperature limits at 100% production tested. All limits at temperature extremes are guaeanteed via
correlating using standard Statistical Quality Control (SQC) methods.
Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programing
resistors can affect switching regulator system performance.
Note 4: Output pin sourcing current. No diode, inductor or capacitor connected to output pin.
Note 5: Feedback pin removed from output and connected to 0 V.
Note 6: Feedback pin removed from output and connected to +12V for the 3.3V, 5V, and the ADJ. version, and +25V
for the 12V and 15V version, to force the output transistir switch OFF.
Note 7: VIN=36V.
Note 8: Junction to ambient theraml resistance (no external heat sink) for the 5 lead TO220 package mounted
verticallly, with 1/2 inch leads in a socket, or on a PC board with minimum cooper area.
Note 9: Junction to ambient thermal resistance ( no extermal heat sink) for the 5 lead TO200 pckage mounted
vertically, with 1/4 inch leads soldered to a PC board contaning approximately 4 square inches of copper area
surrounding the leads.
Note 10: If the TO263-5L package is used, the thermal resistance can be reduced by increasing the PC board copper
area hermally to the package. Using 0.5 square inches of copper area θJA=50/W, with 1 square inch of copper area,
θJA=37/W, and with 1.6 or more square inches of cooper area θJA=32/W.
Note 11: The oscillator frequency reduces to approximately 11KHz in the event of an output short or an overload
which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. The self-
protection feature lowers the average power dissipation of the minimum duty cycle from 5% to approximately 2%.
Page4-9
Rev. 1.3 Mar. 02, 2006

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OCP2576
Simple Switch 3A Step-down Voltage Regulator
„ Typical Performance Characteristics
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
-50
Normalized Output Voltage
VIN=20V, ILOAD=500mA
Normalized at TJ=25
-25 0 25 50 75 100
Junction Temperature ()
125
Line Regulation
1.4
1.2
1.0
ILOAD=500mA
TJ=25
0.8
0.6 3.3V, 5.0V and ADJ
0.4
0.2
0
-0.2 12V and 15V
-0.4
-0.6
0 5.0 10 15 20 25 30
Input Voltage (V)
35
Oscillator Frequency
10
8.0
6.0
VIN=12V
Normalized at 25
4.0
2.0
0
-2.0
-4.0
-6.0
-8.0
-10
-50 -25 0 25 50 75 100
Junction Temperature ()
125
Current Limit
6.5
VIN=25V
6.0
5.5
5.0
4.5
4.0
-50
-25 0 25 50 75 100 125
Junction Temperature ()
Page5-9
Rev. 1.3 Mar. 02, 2006