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.
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 I
Q
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
•
•
•
•
•
Typical Applications
7V–40V
Unregulated
DC Input
+V
IN
+
C
IN
100µF
LM2575-5.0 Output L1
2
330µH
3
5
Gnd On/Off
D1
1N5822
1
4
Feedback
+5V, 1A
Regulated
Output
+
C
OUT
330µF
7V–40V
Unregulated
DC Input
1
4
LM2575
Feedback
+V
IN
+
C
IN
100µF
3
5
Gnd On/Off
Output L1
2
330µH
D1
1N5822
+5V, 1A
Regulated
Output
+
C
OUT
330µF
R2 3.09k
R1 1k
Note: Pin numbers are for TO-220 Package
Note: Pin numbers are for TO-220 Package
V
OUT
= 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
August 2005
1
M9999-082605-B
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
LM2576WT*
†
LM2576-3.3WT
†
LM2576-5.0WT
†
LM2576-12WT
†
LM2576WU*
LM2576-3.3WU
LM2576-5.0WU
LM2576-12WU
Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
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
* 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
M9999-082605-B
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August 2005
LM2576
Micrel, Inc.
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 = 1.5kΩ
FB Pin
Lead Temperature (soldering, 10 sec.)
Maximum Junction Temperature
45V
–0.3V
≤
V
≤
+40V
–1V
Internally Limited
–65°C to +150°C
2 kV
1 kV
260°C
150°C
Operating Ratings
Temperature Range
Supply Voltage
–40°C
≤
T
J
≤
+125°C
40V
Electrical Characteristics
Specifications with standard typeface are for T
J
= 25°C, and those with
boldface type
apply
over
full Operating Temperature Range.
Unless otherwise specified, V
IN
= 12V, and I
LOAD
= 500mA.
LM2576
Parameter
Conditions
Typ
Limit
(Note 2)
Units
(Limits)
Symbol
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS
(Note 3) Test Circuit
Figure 1
V
OUT
Feedback Voltage
V
IN
= 12V , I
LOAD
= 0.5A
V
OUT
= 5V
0.5A
≤
I
LOAD
≤
3A, 8V
≤
V
IN
≤
40V
V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 3A, V
OUT
= 5V
V
IN
= 12V , I
LOAD
= 0.5A
V
OUT
= 3.3V
0.5A
≤
I
LOAD
≤
3A, 6V
≤
V
IN
≤
40V
V
OUT
= 3.3V
V
IN
= 12V, I
LOAD
= 3A
V
IN
= 12V , I
LOAD
= 0.5A
V
OUT
= 5V
0.5A
≤
I
LOAD
≤
3A, 8V
≤
V
IN
≤
40V
V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 3A
V
IN
= 25V , I
LOAD
= 0.5A
V
OUT
= 12V
0.5A
≤
I
LOAD
≤
3A, 15V
≤
V
IN
≤
40V
V
OUT
= 12V
V
IN
= 25V, I
LOAD
= 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)
%
V
OUT
Feedback Voltage
LM2576
Efficiency
η
SYSTEM PARAMETERS, 3.3V REGULATORS
(Note 3) Test Circuit
Figure 1
V
OUT
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)
%
V
OUT
Output Voltage
LM2576-3.3
Efficiency
η
SYSTEM PARAMETERS, 5V REGULATORS
(Note 3) Test Circuit
Figure 1
V
OUT
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)
%
V
OUT
Output Voltage
LM2576-5.0
Efficiency
η
SYSTEM PARAMETERS, 12V REGULATORS
(Note 3) Test Circuit
Figure 1
V
OUT
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)
%
V
OUT
Output Voltage
LMLM2576-12
Efficiency
η
August 2005
3
M9999-082605-B
LM2576
Micrel, Inc.
Electrical Characteristics (continued)
LM2576
Symbol
Parameter
Conditions
Typ
Limit
(Note 2)
Units
(Limits)
DEVICE PARAMETERS, ADJUSTABLE REGULATOR
I
B
f
O
Feedback Bias Current
V
OUT
= 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
I
OUT
= 3A (Note 4)
(Note 5)
Peak Current, t
ON
≤
3µs (Note 4)
1.4
1.8/2.0
98
93
I
CL
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)
µA
µA(max)
°C/W
V
SAT
DC
I
L
Output Leakage Current
V
IN
= 40V, (Note 6),
(Note 6)
Output = 0V
Output = –1V
Output = –1V
I
Q
I
STBY
θ
JA
θ
JA
θ
JC
Quiescent Current
(Note 6)
M9999-082605-B
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August 2005
LM2576
Micrel, Inc.
Electrical Characteristics
(continued)
LM2576
Symbol
Parameter
Conditions
Typ
Limit
(Note 2)
Units
(Limits)
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS
Test Circuit
Figure 1
V
IH
V
IL
I
IH
I
IL
Note 1:
ON/OFF Pin Logic
Input Level
ON /OFF Pin Logic
Current
V
OUT
= 0V
V
OUT
= 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)
µA
µA(max)
µA
µA(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 = 25˚C
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
August 2005
5
M9999-082605-B
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