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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 200A standby current. The output switch includes cycle-bycycle current limiting and thermal shutdown for full protection under fault conditions.
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 < 200A * 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
Typical Applications
7V-40V Unregulated DC Input
+VIN + CIN 100F
LM2575-5.0 Output L1 2 330H 3 5 Gnd On/Off D1 1N5822
1
4
Feedback
+5V, 1A Regulated Output + COUT 330F
7V-40V Unregulated DC Input
1
4 LM2575
Feedback
+VIN + CIN 100F
3 5 Gnd On/Off
Output L1 2 330H D1 1N5822
+5V, 1A Regulated Output + COUT 330F R2 3.09k R1 1k
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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LM2576
Micrel, Inc.
Ordering Information
Part Number Standard RoHS Compliant** LM2576BT* LM2576-3.3BT LM2576-5.0BT LM2576-12BT LM2576BU* LM2576-3.3BU LM2576-5.0BU LM2576-12BU

Range -40C to +85C
Temperature Package TO-220-5 TO-220-5 TO-220-5 TO-220-5 TO-263-5 TO-263-5 TO-263-5 TO-263-5
LM2576WT* LM2576-3.3WT LM2576-5.0WT LM2576-12WT LM2576WU* LM2576-3.3WU LM2576-5.0WU LM2576-12WU

-40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
* 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)
GND 5- ON/OFF 4- FEEDBACK 3- GROUND 2- OUTPUT 1- VIN GND
5-LEAD TO-263 (U)
5- ON/OFF 4- FEEDBACK 3- GROUND 2- OUTPUT 1- VIN
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Absolute Maximum Ratings (Note 1)
Maximum Supply Voltage ON/OFF Pin Input Voltage Output Voltage to Ground (Steady State) Power Dissipation Storage Temperature Range Minimum ESD Rating C = 100pF, R = 1.5k FB Pin Lead Temperature (soldering, 10 sec.) Maximum Junction Temperature 45V -0.3V V +40V -1V Internally Limited -65C to +150C 2 kV 1 kV 260C 150C
Operating Ratings
Temperature Range Supply Voltage -40C TJ +125C 40V
Electrical Characteristics
Specifications with standard typeface are for TJ = 25C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 500mA. LM2576 Parameter Conditions Typ Limit (Note 2) Units (Limits)
Symbol
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit Figure 1 VOUT Feedback Voltage VIN = 12V , ILOAD = 0.5A VOUT = 5V 0.5A ILOAD 3A, 8V VIN 40V VOUT = 5V VIN = 12V, ILOAD = 3A, VOUT = 5V VIN = 12V , ILOAD = 0.5A VOUT = 3.3V 0.5A ILOAD 3A, 6V VIN 40V VOUT = 3.3V VIN = 12V, ILOAD = 3A VIN = 12V , ILOAD = 0.5A VOUT = 5V 0.5A ILOAD 3A, 8V VIN 40V VOUT = 5V VIN = 12V, ILOAD = 3A VIN = 25V , ILOAD = 0.5A VOUT = 12V 0.5A ILOAD 3A, 15V VIN 40V VOUT = 12V VIN = 25V, ILOAD = 3A 1.230 1.217 1.243 1.230 1.193/1.180 1.267/1.280 82 V V(min) V(max) V V(min) V(max) %
VOUT
Feedback Voltage LM2576 Efficiency
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit Figure 1 VOUT Output Voltage 3.3 3.234 3.366 3.3 3.168/3.135 3.432/3.465 75 V V(min) V(max) V V(min) V(max) %
VOUT
Output Voltage LM2576-3.3 Efficiency
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit Figure 1 VOUT Output Voltage 5.0 4.900 5.100 5.0 4.800/4.750 5.200/5.250 82 V V(min) V(max) V V(min) V(max) %
VOUT
Output Voltage LM2576-5.0 Efficiency
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit Figure 1 VOUT Output Voltage 12 11.760 12.240 12 11.520/11.400 12.480/12.600 88 V V(min) V(max) V V(min) V(max) %
VOUT
Output Voltage LMLM2576-12 Efficiency
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Electrical Characteristics (continued)
LM2576 Symbol Parameter Conditions Typ Limit (Note 2) Units (Limits)
DEVICE PARAMETERS, ADJUSTABLE REGULATOR IB fO Feedback Bias Current VOUT = 5V 50 100/500 nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS Oscillator Frequency 52 47/42 58/63 Saturation Voltage Max Duty Cycle (ON) Current Limit IOUT = 3A (Note 4) (Note 5) Peak Current, tON 3s (Note 4) 1.4 1.8/2.0 98 93 ICL 5.8 4.2/3.5 6.9/7.5 2 7.5 30 5 10 Standby Quiescent Current Thermal Resistance ON/OFF Pin = 5V (OFF) T,U Package, Junction to Ambient (Note 7) T,U Package, Junction to Ambient (Note 8) T,U Package, Junction to Case 50 200 65 45 2 kHz kHz (min) kHz (max) V V(max) % %(min) A A(min) A(max) mA(max) mA mA(max) mA mA(max) A A(max) C/W
VSAT DC
IL
Output Leakage Current
VIN = 40V, (Note 6), (Note 6)
Output = 0V Output = -1V Output = -1V
IQ ISTBY JA JA JC
Quiescent Current
(Note 6)
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Electrical Characteristics (continued)
LM2576 Symbol Parameter Conditions Typ Limit (Note 2) Units (Limits)
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit Figure 1 VIH VIL IIH IIL
Note 1:
ON/OFF Pin Logic Input Level ON /OFF Pin Logic Current
VOUT = 0V VOUT = 5V ON /OFF Pin = 5V (OFF) ON/OFF Pin = 0V (ON)
1.4 1.2 4
2.2/2.4 1.0/0.8 30
V(min) V(max) A A(max) A A(max)
0.01 10
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. 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. 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. Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output. Feedback (pin 4) removed from output and connected to 0V. Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF. 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. 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. Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper will lower thermal resistance further.
Note 2: Note 3:
Note 4: Note 5: Note 6: Note 7: Note 8: Note 9:
Typical Performance Characteristics
Normalized Feedback Voltage*
NORMALIZED FEEDBACK VOLTAGE (mV)
Feedback Voltage vs Duty Cycle*
20
FEEDBACK VOLTAGE CHANGE (mV)
25 20 15 10 5 0 -5 -10 -15 -20 -25 -75 -50 -25 0 VIN = 12V ILOAD = 200mA Normalized to TJ = 25C
ILOAD = 200 mA 15 10 5 0 -5 -10 -15 -20 0 20 40 60 80 100
DUTY CYCLE (%)
VIN = 40V
VIN = 7V
25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
* Adjustable version only
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Micrel, Inc.
(Circuit of Figure 1)
Typical Performance Characteristics (continued)
Supply Current vs. Duty Cycle
Supply Current
20 18
SUPPLY CURRENT (mA)
Standby Quiescent Current
STANDBY QUIESCENT CURRENT (A)
16 14 12 10 8 6 4 0 10 20 30
SUPPLY CURRENT (mA)
Measured at Ground Pin TJ = 25C VOUT = 5V
20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 VIN from 7V to 40V 0 20 40 60 80 100 ILOAD = 200 mA
200
VIN = 40V
150 VON/OFF = 5V VIN = 12V 50
100
ILOAD to 1A
40
50
60
0
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
INPUT VOLTAGE (V)
DUTY CYCLE (%)
Current Limit
3 VI N = 25V
SATURATION VOLTAGE (V) OUTPUT CURRENT (A)
Switch Saturation Voltage
1.2 100 95 1.0 -55C -40C 0.8 25C
EFFICIENCY (%)
Efficiency
VOUT = 12V
1A
90 85 80 75 70 65 60 0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 25 30
INPUT VOLTAGE (V)
2
200 mA
200 mA
1
1A VOUT = 3V
0.6 125C 150C 0.4
SWITCH CURRENT (A)
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
35 40
Minimum Operating Voltage
NORMALIZED FEEDBACK VOLTAGE (mV)
Line Regulation
Normalized to V IN = 10V VOUT = 5V ILOAD = 500mA TJ = 25
STANDBY QUIESCENT CURRENT (A)
Feedback Pin Current
100 75 50 25 0 -25 -50 -75 -100 -75 -50 -25 0 25 50 75 100 125 150
5.0 4.5 4.0
INPUT VOLTAGE (V)
14 12 10 8 6 4 2 0 -2 -4 -6 0
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -75 -50 -25 0 VOUT = 1.23V ILOAD = 200 mA 25 50 75 100 125 150
5
10
15
20
25
30
JUNCTION TEMPERATURE (C)
INPUT VOLTAGE (V)
JUNCTION TEMPERATURE (C)
Normalized Output Voltage
100
OUTPUT VOLTAGE CHANGE (mV)
Oscillator Frequency
+8 +6
NORMALIZED FREQUENCY (%)
Dropout Voltage
2.0
INPUT-OUTPUT DIFFERENTIAL (V)
75 50 25 0 -25 -50 -75
VIN = 12V ILOAD = 200mA Normalized to TJ = 25C
Normalized at 25C 1.5 ILOAD = 1A
VOUT = 5% R IND = 0.2
+4 +2 0 -2 -4 --6 VIN = 40V
1.0 ILOAD = 200 mA
0.5
-100 -75 -50 -25 0
25 50 75 100 125 150
VIN = 12V -8 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
JUNCTION TEMPERATURE (C)
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Micrel, Inc.
Typical Performance Characteristics (Circuit of Figure 1)
Load Transient Response
+100mV Output Voltage Change 0 -100mV
3A 2A 1A 0 100 S/div.
Output Current
Switching Waveforms 50V A 0 4A B 2A 0 4A C 2A 0 D 5 S/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: 5S/div
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Micrel, Inc.
Test Circuits and Layout Guidelines
FEEDBACK +VIN 1 7V - 40V UNREGULATED DC INPUT + 100 F CIN GND 3 ON/OFF 5 2 4
LM2575
OUTPUT
L1 330 H D1 MBR360
VOUT 5.00V + COUT 470F R2 R1 L O A D
CIN -- 100F, 75V Aluminum Electrolytic COUT -- 470F, 15V Aluminum Electrolytic D1 -- Schottky, MBR360 L1 -- 330H, 415-0926 (AIE) R1 -- 1k, 0.01% R2 -- 3.065k, 0.01% 5-pin TO-220 socket--2936 (Loranger Mfg. Co.) 4-pin TO-3 socket--8112-AG7 (Augat Inc.)
FEEDBACK +VIN 1 7V - 40V UNREGULATED DC INPUT + 100 F CIN GND 3 ON/OFF 5 2 4
LM2575-5.0
OUTPUT
L1 330 H D1 11DQ06
VOUT 5.00V + COUT 220F L O A D
CIN -- 100F, 75V Aluminum Electrolytic COUT -- 330F, 15V Aluminum Electrolytic D1 -- Schottky, 11DQ06 L1 -- 100H, 415-0926 (AIE) 5-pin TO-220 socket--2936 (Loranger Mfg. Co.) 4-pin TO-3 socket--8112-AG7 (Augat Inc.)
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 FEEDBACK
1 4
3.1k
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
V IN
1
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
FIXED GAIN ERROR AMP
FIXED GAIN ERROR AMP COMPARATOR 3 AMP SWITCH FEEDBACK
+
1.0k
4
+ + -
COMPARATOR
3 AMP SWITCH
-
+ -
DRIVER
DRIVER
2
1.23V BAND-GAP REFERENCE
OUTPUT 1.23V BAND-GAP REFERENCE
2
OUTPUT
52 kHz OSCILLATOR
RESET
THERMAL SHUTDOWN
CURRENT LIMIT
3
GND
52 kHz OSCILLATOR
RESET
THERMAL SHUTDOWN
CURRENT LIMIT
3
GND
Note: Pin numbers are for the TO-220 package
Fixed Regulator
Adjustable Regulator
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LM2576
Micrel, Inc.
Package Information
0.150 D 0.005 (3.81 D 0.13) 0.400 0.015 (10.16 0.38) 0.108 0.005 (2.74 0.13) 0.241 0.017 (6.12 0.43) 0.177 0.008 (4.50 0.20) 0.050 0.005 (1.27 0.13)
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) 0.268 REF (6.81 REF)
0.032 0.005 (0.81 0.13)
0.018 0.008 (0.46 0.20)
0.103 0.013 (2.620.33)
Dimensions: inch (mm)
5-Lead TO-220 (T)
0.4050.005 0.065 0.010 202 0.0500.005
0.176 0.005 0.060 0.005
0.3600.005 0.6000.025 SEATING PLANE 0.004 +0.004 -0.008
0.0670.005 DIM. = INCH
0.032 0.003
8 MAX 0.015 0.002
0.100 0.01
5-Lead TO-263 (U)
MICREL INC. 2180 FORTUNE DRIVE
TEL
SAN JOSE, CA 95131
WEB
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 474-1000
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. (c) 2005 Micrel, Incorporated.
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