August 2005 1 M9999-082605-B
LM2576 Micrel, Inc.
LM2576
52kHz Simple 3A Buck Regulator
General Description
The LM2576 series of monolithic integrated circuits provide
all the active functions for a step-down (buck) switching
regulator. Fixed versions are available with a 3.3V, 5V, or 12V
fixed output. Adjustable versions have an output voltage
range from 1.23V to 37V. Both versions are capable of driving
a 3A load with excellent line and load regulation.
These regulators are simple to use because they require a
minimum number of external components and include internal
frequency compensation and a fixed-frequency oscillator.
The LM2576 series offers a high efficiency replacement for
popular three-terminal adjustable linear regulators. It
substantially reduces the size of the heat sink, and in many
cases no heat sink is required.
A standard series of inductors available from several different
manufacturers are ideal for use with the LM2576 series. This
feature greatly simplifies the design of switch-mode power
supplies.
The feedback voltage is guaranteed to ±2% tolerance for
adjustable versions, and the output voltage is guaranteed to
±3% for fixed versions, within specified input voltages and
output load conditions. The oscillator frequency is guaranteed
to ±10%. External shutdown is included, featuring less than
200µA standby current. The output switch includes cycle-by-
cycle current limiting and thermal shutdown for full protection
under fault conditions.
Typical Applications
Features
3.3V, 5V, 12V, and adjustable output versions
Voltage over specified line and load conditions:
Fixed version: ±3% max. output voltage
Adjustable version: ±2% max. feedback voltage
Guaranteed 3A output current
Wide input voltage range:
4V to 40V
Wide output voltage range
1.23V to 37V
Requires only 4 external components
52kHz fixed frequency internal oscillator
Low power standby mode IQ typically < 200µA
80% efficiency (adjustable version typically > 80%)
Uses readily available standard inductors
Thermal shutdown and current limit protection
100% electrical thermal limit burn-in
Applications
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to negative converter (inverting Buck-Boost)
Isolated Flyback Converter using minimum number of
external components
Negative Boost Converter
R2
R1
7V40V
Unregulated
DC Input LM2575
+
C
IN
100µF
+V
IN
1
3
Gnd 5
On/Off
2
Output
4Feedback
L1
330µH +
D1
1N5822 C
OUT
330µF
R2 3.09k
R1 1k
V
OUT
= 1.23 1 +
( )
+5V, 1A
Regulated
Output
Note: Pin numbers are for TO-220 Package
7V40V
Unregulated
DC Input LM2575-5.0
+
C
IN
100µF
+V
IN
1
3
Gnd 5
On/Off
2
Output
4Feedback
L1
330µH +
D1
1N5822 C
OUT
330µF
+5V, 1A
Regulated
Output
Note: Pin numbers are for TO-220 Package
Fixed Regulator in Typical Application Adjustable Regulator in Fixed Output Application
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
M9999-082605-B 2 August 2005
LM2576 Micrel, Inc.
Part NumberTemperature
Standard RoHS Compliant** Range Package
LM2576BT*LM2576WT*40°C to +85°C TO-220-5
LM2576-3.3BTLM2576-3.3WT40°C to +85°C TO-220-5
LM2576-5.0BTLM2576-5.0WT40°C to +85°C TO-220-5
LM2576-12BTLM2576-12WT40°C to +85°C TO-220-5
LM2576BU* LM2576WU* 40°C to +85°C TO-263-5
LM2576-3.3BU LM2576-3.3WU 40°C to +85°C TO-263-5
LM2576-5.0BU LM2576-5.0WU 40°C to +85°C TO-263-5
LM2576-12BU LM2576-12WU 40°C to +85°C TO-263-5
* Adjustable output regulators.
**RoHS compliant with "hot-melting solder" exemption.
Contact factory for bent or staggered leads option.
Pin Configurations
GND 5- ON/OFF
4- FEEDBACK
3- GROUND
2- OUTPUT
1- VIN
5-LEAD TO-263 (U)
GND 5- ON/OFF
4- FEEDBACK
3- GROUND
2- OUTPUT
1- VIN
5-LEAD TO-220 (T)
Ordering Information
August 2005 3 M9999-082605-B
LM2576 Micrel, Inc.
Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply
over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 500mA.
LM2576
Symbol Parameter Conditions Typ Limit Units
(Note 2) (Limits)
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit
Figure 1
VOUT Feedback Voltage VIN = 12V , ILOAD = 0.5A 1.230 V
VOUT = 5V 1.217 V(min)
1.243 V(max)
VOUT Feedback Voltage 0.5A ILOAD 3A, 8V VIN 40V 1.230 V
LM2576 VOUT = 5V 1.193/1.180 V(min)
1.267/1.280 V(max)
ηEfficiency VIN = 12V, ILOAD = 3A, VOUT = 5V 82 %
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit
Figure 1
VOUT Output Voltage VIN = 12V , ILOAD = 0.5A 3.3 V
VOUT = 3.3V 3.234 V(min)
3.366 V(max)
VOUT Output Voltage 0.5A ILOAD 3A, 6V VIN 40V 3.3 V
LM2576-3.3 VOUT = 3.3V 3.168/3.135 V(min)
3.432/3.465 V(max)
ηEfficiency VIN = 12V, ILOAD = 3A 75 %
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit
Figure 1
VOUT Output Voltage VIN = 12V , ILOAD = 0.5A 5.0 V
VOUT = 5V 4.900 V(min)
5.100 V(max)
VOUT Output Voltage 0.5A ILOAD 3A, 8V VIN 40V 5.0 V
LM2576-5.0 VOUT = 5V 4.800/4.750 V(min)
5.200/5.250 V(max)
ηEfficiency VIN = 12V, ILOAD = 3A 82 %
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit
Figure 1
VOUT Output Voltage VIN = 25V , ILOAD = 0.5A 12 V
VOUT = 12V 11.760 V(min)
12.240 V(max)
VOUT Output Voltage 0.5A ILOAD 3A, 15V VIN 40V 12 V
LMLM2576-12 VOUT = 12V 11.520/11.400 V(min)
12.480/12.600 V(max)
ηEfficiency VIN = 25V, ILOAD = 3A 88 %
Operating Ratings
Temperature Range 40°C TJ +125°C
Supply Voltage 40V
Absolute Maximum Ratings (Note 1)
Maximum Supply Voltage 45V
ON/OFF Pin Input Voltage 0.3V V +40V
Output Voltage to Ground (Steady State) 1V
Power Dissipation Internally Limited
Storage Temperature Range 65°C to +150°C
Minimum ESD Rating
C = 100pF, R = 1.5k2 kV
FB Pin 1 kV
Lead Temperature (soldering, 10 sec.) 260°C
Maximum Junction Temperature 150°C
M9999-082605-B 4 August 2005
LM2576 Micrel, Inc.
Electrical Characteristics (continued)
LM2576 Units
Symbol Parameter Conditions Typ Limit (Limits)
(Note 2)
DEVICE PARAMETERS, ADJUSTABLE REGULATOR
IBFeedback Bias Current VOUT = 5V 50 100/500 nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
fOOscillator Frequency 52 kHz
47/42 kHz (min)
58/63 kHz (max)
VSAT Saturation Voltage IOUT = 3A (Note 4) 1.4 V
1.8/2.0 V(max)
DC Max Duty Cycle (ON) (Note 5) 98 %
93 %(min)
ICL Current Limit Peak Current, tON 3µs (Note 4) 5.8 A
4.2/3.5 A(min)
6.9/7.5 A(max)
ILOutput Leakage Current VIN = 40V, (Note 6), Output = 0V 2 mA(max)
Output = 1V 7.5 mA
(Note 6) Output = 1V 30 mA(max)
IQQuiescent Current (Note 6) 5 mA
10 mA(max)
ISTBY Standby Quiescent ON/OFF Pin = 5V (OFF) 50 µA
Current 200 µA(max)
θJA Thermal Resistance T,U Package, Junction to Ambient (Note 7) 65 °C/W
θJA T,U Package, Junction to Ambient (Note 8) 45
θJC T,U Package, Junction to Case 2
August 2005 5 M9999-082605-B
LM2576 Micrel, Inc.
Electrical Characteristics (continued)
LM2576 Units
Symbol Parameter Conditions Typ Limit (Limits)
(Note 2)
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit
Figure 1
VIH ON/OFF Pin Logic VOUT = 0V 1.4 2.2/2.4 V(min)
VIL Input Level VOUT = 5V 1.2 1.0/0.8 V(max)
IIH ON /OFF Pin Logic ON /OFF Pin = 5V (OFF) 4 µA
Current 30 µA(max)
IIL ON/OFF Pin = 0V (ON) 0.01 µA
10 µA(max)
Note 1: Absolute Maximum Rating indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device
is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test 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 are
100% production tested. All limits at temperature extreme are guaranteed via testing.
Note 3: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the
LM2576/LM1576 is used as shown in
Figure 1
test circuit, system performance will be shown in system parameters section of Electrical
Characteristics.
Note 4: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output.
Note 5: Feedback (pin 4) removed from output and connected to 0V.
Note 6: Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.
Note 7: Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/2" leads in a socket, or
on PC board with minimum copper area.
Note 8: Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/4" leads soldered to PC
board containing approximately 4 square inches of copper area surrounding the leads.
Note 9: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper will lower
thermal resistance further.
Typical Performance Characteristics
Normalized
Feedback Voltage*
JUNCTION TEMPERATURE (˚C)
NORMALIZED FEEDBACK VOLTAGE (mV)
25
20
15
10
5
0
-5
-10
-15
-20
-25
-75 -50 -25 0 25 50 75 100125150
VIN = 12V
ILOAD = 200mA
Normalized to TJ = 25˚C
Feedback Voltage
vs Duty Cycle*
DUTY CYCLE (%)
FEEDBACK VOLTAGE CHANGE (mV)
20
15
10
5
0
-5
-10
-15
-20
ILOAD = 200 mA
VIN = 40V
VIN = 7V
0 20 40 60 80 100
* Adjustable version only
M9999-082605-B 6 August 2005
LM2576 Micrel, Inc.
Typical Performance Characteristics (continued) (Circuit of
Figure 1
)
Supply Current
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
20 Measured at
Ground Pin
TJ = 25˚C
VOUT = 5V
18
16
14
12
10
8
6
40102030405060
ILOAD to 1A
Supply Current
vs. Duty Cycle
DUTY CYCLE (%)
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
00 20 40 60 80 100
VIN from 7V to 40V
ILOAD = 200 mA
SUPPLY CURRENT (mA)
JUNCTION TEMPERATURE (˚C)
200
150
100
50
0
-75
VIN = 12V
STANDBY QUIESCENT CURRENT (µA)
Standby
Quiescent Current
VIN = 40V
-50 -25 0 25 50 75 100 125150
Current Limit
JUNCTION TEMPERATURE (˚C)
3
2
1
0
-75
VIN = 25V
OUTPUT CURRENT (A)
INPUT VOLTAGE (V)
100
EFFICIENCY (%)
Efficiency
VOUT = 12V
-50 -25 0 25 50 75 100125 150
95
90
85
80
75
70
65
60
200 mA
200 mA
VOUT = 3V
1A
0 5 10 15 20 25 30 35 40
Minimum Operating
Voltage
JUNCTION TEMPERATURE (˚C)
5.0
ILOAD = 200 mA
INPUT VOLTAGE (V)
Line Regulation
INPUT VOLTAGE (V)
14
0
NORMALIZED FEEDBACK VOLTAGE (mV)
JUNCTION TEMPERATURE (˚C)
100
-100
-75
STANDBY QUIESCENT CURRENT (µA)
Feedback Pin Current
-50 -25 0 25 50 75 100 125150
VOUT = 1.23V
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-75 -50 -25 0 25 50 75 100125150
12
10
8
6
4
2
0
-2
-4
-6 51015202530
75
50
25
0
-25
-50
-75
JUNCTION TEMPERATURE (˚C)
+8
-8
-75
NORMALIZED FREQUENCY (%)
Oscillator Frequency
-50 -25 0 25 50 75 100125150
+6
+4
+2
0
-2
-4
--6 VIN = 12V
VIN = 40V
Normalized at 25˚C
Normalized to VIN = 10V
VOUT = 5V
ILOAD = 500mA
TJ = 25
VON/OFF = 5V
Switch
Saturation Voltage
SWITCH CURRENT (A)
1.2
-55˚C
1.0
0.8
0.6
0.4 0
SATURATION VOLTAGE (V)
0.2 0.4 0.6 0.8 1.0
25˚C
125˚C
150˚C
-40˚C
Dropout Voltage
JUNCTION TEMPERATURE (˚C)
INPUT-OUTPUT DIFFERENTIAL (V)
2.0
-75 -50 -25 0 25 50 75 100125150
VOUT = 5%
RIND = 0.2
ILOAD = 1A
ILOAD = 200 mA
1.5
1.0
0.5
0
Normalized
Output Voltage
JUNCTION TEMPERATURE (˚C)
OUTPUT VOLTAGE CHANGE (mV)
100
75
50
25
0
-25
-50
-75
-100
-75 -50 -25 0 25 50 75 100125150
VIN = 12V
ILOAD = 200mA
Normalized to TJ = 25˚C
1A
August 2005 7 M9999-082605-B
LM2576 Micrel, Inc.
100 µS/div.
Load Transient Response
+100mV
0
-100mV
Output
Voltage
Change
3A
2A
1A
0
Output
Current
50V
0
4A
2A
0
4A
2A
0
A
B
C
D
5 µS/div.
Switching Waveforms
A: Output pin voltage 50V/div
B: Output pin current 2A/div
C: Inductor current 2A/div
D: Output ripple voltage 50 mV/div., AC coupled
Horizontal Time Base: 5µS/div
VOUT = 5V VIN = 45V
Typical Performance Characteristics (Circuit of
Figure 1
)
M9999-082605-B 8 August 2005
LM2576 Micrel, Inc.
LM2575
+100 µF
+V
IN
1
3GND 5ON/OFF 2
OUTPUT
4FEEDBACK
L1
330 µH +
D1
MBR360
C
OUT
470µF R2
R1
V
OUT
5.00V
7V - 40V
UNREGULATED
DC INPUT C
IN
L
O
A
D
C
IN
100µF, 75V Aluminum Electrolytic
C
OUT
470µF, 15V Aluminum Electrolytic
D1 Schottky, MBR360
L1 330µH, 415-0926 (AIE)
R1 1k, 0.01%
R2 3.065k, 0.01%
5-pin TO-220 socket2936 (Loranger Mfg. Co.)
4-pin TO-3 socket8112-AG7 (Augat Inc.)
LM2575-5.0
+100 µF
+V
IN
1
3GND 5ON/OFF 2
OUTPUT
4FEEDBACK
L1
330 µH +
D1
11DQ06
C
OUT
220µF
V
OUT
5.00V
Note: Pin numbers are for TO-220 Package
7V - 40V
UNREGULATED
DC INPUT C
IN
C
IN
100µF, 75V Aluminum Electrolytic
C
OUT
330µF, 15V Aluminum Electrolytic
D1 Schottky, 11DQ06
L1 100µH, 415-0926 (AIE)
5-pin TO-220 socket2936 (Loranger Mfg. Co.)
4-pin TO-3 socket8112-AG7 (Augat Inc.)
L
O
A
D
ON/OFF
COMPARATOR
FIXED GAIN
ERROR AMP
3 AMP
SWITCH
OUTPUT
DRIVER
+
-
+
-
VIN
FEED-
BACK
1.23V
BAND-GAP
REFERENCE 52 kHz
OSCILLATOR RESET THERMAL
SHUTDOWN CURRENT
LIMIT
5
2
3
1
Note: Pin numbers are for the TO-220 package
INTERNAL
REGULATOR ON/OFF
GND
ON/OFF
COMPARATOR
FIXED GAIN
ERROR AMP
3 AMP
SWITCH
OUTPUT
DRIVER
+
-
+
-
VIN
FEED-
BACK
1.23V
BAND-GAP
REFERENCE 52 kHz
OSCILLATOR RESET THERMAL
SHUTDOWN CURRENT
LIMIT
5
2
3
1
4
INTERNAL
REGULATOR ON/OFF
GND
3.1k
1.0k
4
Block Diagrams
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance generate voltage transients
which can cause problems. For minimal stray inductance and ground loops, the length of the leads indicated by heavy lines should be kept as
short as possible. Single-point grounding (as indicated) or ground plane construction should be used for best results.
Fixed Regulator Adjustable Regulator
Test Circuits and Layout Guidelines
Figure 1.
August 2005 9 M9999-082605-B
LM2576 Micrel, Inc.
Package Information
0.018 ±0.008
(0.46 ±0.20)
0.268 REF
(6.81 REF)
0.032 ±0.005
(0.81 ±0.13)
0.550 ±0.010
(13.97 ±0.25)
7°
Typ.
SEATING
PLANE
0.578 ±0.018
(14.68 ±0.46)
0.108 ±0.005
(2.74 ±0.13)
0.050 ±0.005
(1.27 ±0.13)
0.150 D ±0.005
(3.81 D ±0.13)
0.400 ±0.015
(10.16 ±0.38)
0.177 ±0.008
(4.50 ±0.20)
0.103 ±0.013
(2.62±0.33)
0.241 ±0.017
(6.12 ±0.43)
0.067 ±0.005
(1.70 ±0.127)
inch
(mm)
Dimensions:
5-Lead TO-220 (T)
0.067±0.005 0.032 ±0.003
0.360±0.005
0.600±0.025
0.405±0.005
0.060±0.005
0.176±0.005
8° MAX 0.100±0.01
0.050±0.005
0.015 ±0.002
0.004+0.004
0.008
SEATING PLANE
0.065±0.010
20°±2°
DIM. = INCH
5-Lead TO-263 (U)
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchasers
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchasers own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.