LM2576 Micrel, Inc.

LM2576
52kHz Simple 3A Buck Regulator

General Description Features

The LM2576 series of monolithic integrated circuits provide • 3.3V, 5V, 12V, and adjustable output versions
all the active functions for a step-down (buck) switching • Voltage over specified line and load conditions:
regulator. Fixed versions are available with a 3.3V, 5V, or 12V Fixed version: ±3% max. output voltage
fixed output. Adjustable versions have an output voltage Adjustable version: ±2% max. feedback voltage
range from 1.23V to 37V. Both versions are capable of driving • Guaranteed 3A output current
a 3A load with excellent line and load regulation.
• Wide input voltage range:
These regulators are simple to use because they require a 4V to 40V
minimum number of external components and include internal • Wide output voltage range
frequency compensation and a fixed-frequency oscillator. 1.23V to 37V
The LM2576 series offers a high efficiency replacement for • Requires only 4 external components
popular three-terminal adjustable linear regulators. It • 52kHz fixed frequency internal oscillator
substantially reduces the size of the heat sink, and in many
cases no heat sink is required. • Low power standby mode IQ typically < 200µA
• 80% efficiency (adjustable version typically > 80%)
A standard series of inductors available from several different
manufacturers are ideal for use with the LM2576 series. This • Uses readily available standard inductors
feature greatly simplifies the design of switch-mode power • Thermal shutdown and current limit protection
supplies. • 100% electrical thermal limit burn-in
The feedback voltage is guaranteed to ±2% tolerance for
adjustable versions, and the output voltage is guaranteed to Applications
±3% for fixed versions, within specified input voltages and • Simple high-efficiency step-down (buck) regulator
output load conditions. The oscillator frequency is guaranteed • Efficient pre-regulator for linear regulators
to ±10%. External shutdown is included, featuring less than
200µA standby current. The output switch includes cycle-by- • On-card switching regulators
cycle current limiting and thermal shutdown for full protection • Positive to negative converter (inverting Buck-Boost)
under fault conditions. • Isolated Flyback Converter using minimum number of
external components
• Negative Boost Converter

Typical Applications

7V–40V 7V–40V
Unregulated +5V, 1A Unregulated +5V, 1A
4 Feedback 4 Feedback
DC Input 1 Regulated DC Input 1 Regulated
LM2575-5.0 Output L1 LM2575
+VIN Output +VIN Output L1 Output
2 330µH 2 330µH
+ 3 5 + + 3 5 + R2 3.09k
CIN Gnd On/Off CIN Gnd On/Off
D1 COUT D1 COUT
100µF 100µF R1 1k
1N5822 330µF 1N5822 330µF

Note: Pin numbers are for TO-220 Package Note: Pin numbers are for TO-220 Package

(
VOUT = 1.23 1 + R2
R1 )

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
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Ordering Information

Part Number‡ Temperature

Standard RoHS Compliant** Range Package
LM2576BT*† LM2576WT*† –40°C to +85°C TO-220-5
† †
LM2576-3.3BT LM2576-3.3WT –40°C to +85°C TO-220-5
† †
LM2576-5.0BT LM2576-5.0WT –40°C to +85°C TO-220-5
† †
LM2576-12BT LM2576-12WT –40°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

5-LEAD TO-220 (T) 5-LEAD TO-263 (U)

GND GND
5- ON/OFF 5- ON/OFF
4- FEEDBACK 4- FEEDBACK
3- GROUND 3- GROUND
2- OUTPUT 2- OUTPUT
1- VIN 1- VIN

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Absolute Maximum Ratings (Note 1) Operating Ratings
Maximum Supply Voltage 45V Temperature Range –40°C ≤ TJ ≤ +125°C
ON/OFF Pin Input Voltage –0.3V ≤ V ≤ +40V Supply Voltage 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 = 1.5kΩ 2 kV
FB Pin 1 kV
Lead Temperature (soldering, 10 sec.) 260°C
Maximum Junction Temperature 150°C

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)
η Efficiency 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)
η Efficiency 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)
η Efficiency 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)
η Efficiency VIN = 25V, ILOAD = 3A 88 %

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Electrical Characteristics (continued)
LM2576 Units
Symbol Parameter Conditions Typ Limit (Limits)
(Note 2)
DEVICE PARAMETERS, ADJUSTABLE REGULATOR
IB Feedback Bias Current VOUT = 5V 50 100/500 nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
fO Oscillator 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)
IL Output Leakage Current VIN = 40V, (Note 6), Output = 0V 2 mA(max)
Output = –1V 7.5 mA
(Note 6) Output = –1V 30 mA(max)
IQ Quiescent 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

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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

Feedback Voltage* vs Duty Cycle*
20
NORMALIZED FEEDBACK VOLTAGE (mV)

25
VIN = 12V ILOAD = 200 mA
20
FEEDBACK VOLTAGE CHANGE (mV)

15
ILOAD = 200mA
15
Normalized to TJ = 25˚C 10
10
5 5 VIN = 40V
0 0
-5 -5
-10 VIN = 7V
-10
-15
-20 -15
-25 -20
-75 -50 -25 0 25 50 75 100 125 150 0 20 40 60 80 100
JUNCTION TEMPERATURE (˚C) DUTY CYCLE (%)

* Adjustable version only

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Typical Performance Characteristics (continued) (Circuit of Figure 1)

Supply Current Standby

Supply Current vs. Duty Cycle Quiescent Current
20 20.0 200
Measured at

STANDBY QUIESCENT CURRENT (µA)

VIN = 40V
18 Ground Pin 17.5
TJ = 25˚C
SUPPLY CURRENT (mA)

SUPPLY CURRENT (mA)

16 VOUT = 5V 15.0 150
14 12.5
VON/OFF = 5V
12 10.0 100
10 7.5 ILOAD = 200 mA
VIN = 12V
8 ILOAD to 1A 5.0 50
6 2.5 VIN from 7V to 40V

4 0 0
0 10 20 30 40 50 60 0 20 40 60 80 100 -75 -50 -25 0 25 50 75 100 125 150
INPUT VOLTAGE (V) DUTY CYCLE (%) JUNCTION TEMPERATURE (˚C)

Switch
Current Limit Saturation Voltage Efficiency
3 1.2 100
VI N = 25V
95 VOUT = 12V
SATURATION VOLTAGE (V)

1A
OUTPUT CURRENT (A)

1.0 90

EFFICIENCY (%)
2 -55˚C
85 200 mA 200 mA
-40˚C
0.8 80
25˚C
75 1A
1
0.6 125˚C 70 VOUT = 3V
150˚C
65

0 0.4 60
-75 -50 -25 0 25 50 75 100 125 150 0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 25 30 35 40
JUNCTION TEMPERATURE (˚C) SWITCH CURRENT (A) INPUT VOLTAGE (V)

Minimum Operating
Voltage Line Regulation Feedback Pin Current
5.0 14 100
NORMALIZED FEEDBACK VOLTAGE (mV)

STANDBY QUIESCENT CURRENT (µA)

4.5 12 Normalized to V IN = 10V

75
VOUT = 5V
4.0 10
ILOAD = 500mA 50
INPUT VOLTAGE (V)

3.5 8
TJ = 25
3.0 6 25

2.5 4 0
2.0 2 -25
1.5 0
VOUT = 1.23V -50
1.0 -2
ILOAD = 200 mA -75
0.5 -4
0 -6 -100
-75 -50 -25 0 25 50 75 100 125 150 0 5 10 15 20 25 30 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C) INPUT VOLTAGE (V) JUNCTION TEMPERATURE (˚C)

Normalized
Output Voltage Oscillator Frequency Dropout Voltage
100 +8 2.0
VIN = 12V Normalized at 25˚C ∆VOUT = 5%
INPUT-OUTPUT DIFFERENTIAL (V)

+6
OUTPUT VOLTAGE CHANGE (mV)

75 ILOAD = 200mA R IND = 0.2Ω

ILOAD = 1A
NORMALIZED FREQUENCY (%)

Normalized to TJ = 25˚C +4 1.5

50
25 +2

0 0 1.0
-25 -2
VIN = 40V ILOAD = 200 mA
-50 -4 0.5
-75 --6
VIN = 12V
-100 -8 0
-75 -50 -25 0 25 50 75 100 125 150 -75 -50 -25 0 25 50 75 100 125 150 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C) JUNCTION TEMPERATURE (˚C) JUNCTION TEMPERATURE (˚C)

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Typical Performance Characteristics (Circuit of Figure 1)

Load Transient Response

+100mV
Output
Voltage 0
Change

-100mV

3A

2A
Output
Current
1A

0
100 µS/div.

Switching Waveforms
50V
A
0

4A

B 2A

4A

C 2A

0
D

5 µS/div.

V OUT = 5V VIN = 45V

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

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Test Circuits and Layout Guidelines

FEEDBACK
+VIN 4
LM2575 L1
VOUT
CIN — 100µF, 75V Aluminum Electrolytic
1 OUTPUT 5.00V
COUT — 470µF, 15V Aluminum Electrolytic
D1 — Schottky, MBR360
7V - 40V 100 µF 2 330 µH + L1 — 330µH, 415-0926 (AIE)
UNREGULATED + GND 3 ON/OFF 5 COUT R2 L
O R1 — 1k, 0.01%
DC INPUT D1 470µF R2 — 3.065k, 0.01%
CIN A
MBR360 5-pin TO-220 socket—2936 (Loranger Mfg. Co.)
R1 D
4-pin TO-3 socket—8112-AG7 (Augat Inc.)

FEEDBACK
+VIN 4
LM2575-5.0 L1
VOUT
CIN — 100µF, 75V Aluminum Electrolytic
1 OUTPUT 5.00V
COUT — 330µF, 15V Aluminum Electrolytic
D1 — Schottky, 11DQ06
7V - 40V 100 µF 2 330 µH + L1 — 100µH, 415-0926 (AIE)
UNREGULATED + GND 3 ON/OFF 5 COUT L 5-pin TO-220 socket—2936 (Loranger Mfg. Co.)
DC INPUT D1 220µF O 4-pin TO-3 socket—8112-AG7 (Augat Inc.)
CIN A
11DQ06
D

Note: Pin numbers are for TO-220 Package

Figure 1.
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.

Block Diagrams

V IN INTERNAL ON/OFF 5 ON/OFF V IN INTERNAL ON/OFF 5 ON/OFF

1 REGULATOR 1 REGULATOR

FEED-
BACK 4
FIXED GAIN FIXED GAIN
3.1k ERROR AMP ERROR AMP
3 AMP FEED- 3 AMP
+ COMPARATOR SWITCH BACK 4 + COMPARATOR SWITCH
1.0k + +
- DRIVER
- DRIVER
- -
2 OUTPUT 2 OUTPUT

1.23V 1.23V
BAND-GAP 52 kHz THERMAL CURRENT BAND-GAP 52 kHz THERMAL CURRENT
REFERENCE OSCILLATOR RESET SHUTDOWN LIMIT REFERENCE OSCILLATOR RESET SHUTDOWN LIMIT
3 GND 3 GND

Note: Pin numbers are for the TO-220 package

Fixed Regulator Adjustable Regulator

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Package Information

0.150 D ±0.005
(3.81 D ±0.13) 0.177 ±0.008
(4.50 ±0.20)
0.400 ±0.015 0.050 ±0.005
(10.16 ±0.38) (1.27 ±0.13)
0.108 ±0.005
(2.74 ±0.13) 0.241 ±0.017
(6.12 ±0.43)

0.578 ±0.018
(14.68 ±0.46)
SEATING
PLANE

7°
Typ.
0.550 ±0.010
(13.97 ±0.25)

0.067 ±0.005
(1.70 ±0.127) 0.032 ±0.005
(0.81 ±0.13) 0.018 ±0.008 0.103 ±0.013
0.268 REF (0.46 ±0.20) (2.62±0.33)
(6.81 REF)
Dimensions: inch
(mm)

5-Lead TO-220 (T)

0.405±0.005 0.176 ±0.005

0.065 ±0.010 0.050±0.005 0.060 ±0.005
20°±2°

0.360±0.005

0.600±0.025

SEATING PLANE
0.004 +0.004
–0.008

8° MAX 0.100 ±0.01

0.067±0.005 0.032 ±0.003
0.015 ±0.002
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 Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.

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