LM2574
Micrel
LM2574
52kHz Simple 0.5A Buck Regulator
General Description
The LM2574 family is a series of easy to use fixed and
adjustable switching voltage regulators. The LM2574 con-
tains all of the active circuitry necessary to construct a
stepdown (buck) switching regulator and requires a minimum
of external components.
The LM2574 is available in 3.3V, 5V, and 12V fixed output
versions, or an adjustable version with an output voltage
range of 1.23V to 37V. Output voltage is guaranteed to
±4%
for specified input and load conditions.
The LM2574 can supply 0.5A while maintaining excellent line
and load regulation. The output switch includes cycle-by-
cycle current limiting, as well as thermal shutdown for full
protection under fault conditions.
An external shutdown connection selects operating or standby
modes. Standby current is less than 200µA.
Heat sinks are generally unnecessary due the regulator’s
high efficiency. Adequate heat transfer is usually provided by
soldering all package pins to a printed circuit board.
The LM2574 includes internal frequency compensation and
an internal 52kHz fixed frequency oscillator guaranteed to
±10%
of the frequency.
Circuits constructed around the LM2574 use a standard
series of inductors which are available from several different
manufacturers.
Features
• 3.3V, 5V, 12V, and Adjustable Output Versions
• Adjustable Version Output 1.23V to 37V
±4%
Max. over
Line and Load Conditions.
• Guaranteed 0.5A Output Current
• Wide Input Voltage, up to 40V
• Thermal Shutdown and Current Limit Protection
• Requires only 4 external Components.
• Shutdown Capability (Standby Mode)
• Low Power Standby Mode < 200µA Typical
• High Efficiency
• 52kHz Fixed Frequency Internal Oscillator
• Uses Standard Inductors
Applications
•
•
•
•
Simple High-efficiency Step-down (Buck) Regulator
Efficient Pre-Regulator for Linear Regulators
On-card Switching Regulators
Positive to Negative Converter (Buck-Boost)
Ordering Information
Part Number
LM2574BN
LM2574BWM
LM2574-3.3BN
LM2574-3.3BWM
LM2574-5.0BN
LM2574-5.0BWM
LM2574-12BN
LM2574-12BWM
Temp. 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
Package
8-pin Plastic DIP
14-pin Wide SOIC
8-pin Plastic DIP
14-pin Wide SOIC
8-pin Plastic DIP
14-pin Wide SOIC
8-pin Plastic DIP
14-pin Wide SOIC
Pin Configuration
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8
7
6
5
*
OUTPUT
*
V
IN
Typical Application
8-pin DIP (N)
40V MAX
UNREGULATED
DC IN
V
IN
*
*
FB
SIG GND
ON/OFF
PWR GND
*
1
2
3
4
5
6
7
14
13
12
11
10
9
8
*
*
OUTPUT
*
V
IN
*
*
FB
LM2574
PWR
GND
SIG
GND
OUT
ON/
OFF
11DQ05
330µH
REGULATED
OUTPUT
0.5A
C
IN
22µF
C
OUT
220µF
14-pin SOIC (WM)
Figure 1. Fixed Output Regulator Circuit
* NC: solder to printed circuit for
maximum heat transfer
August 1999
1
LM2574
LM2574
Micrel
Absolute Maximum Ratings
Maximum Supply Voltage
LM2574 ..................................................................... 45V
OFF Pin Input Voltage ................................ –0.3V
≤
V
≤
V
IN
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 ............................................... 2kV
FB Pin ....................................................................... 1kV
Lead Temperature (soldering, 10 sec.) ..................... 260°C
Maximum Junction Temperature ............................... 150°C
Operating Ratings
Temperature Range
LM2574 ........................................... 40°C
≤
T
J
≤
+125°C
Supply Voltage
LM2574 ..................................................................... 40V
Electrical Characteristics
Symbol
Parameter
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
= 100mA.
Condition
Min
Typ
Max
Units
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS
(Note 3) Test Circuit
Figure 2
V
OUT
V
OUT
η
Feedback Voltage
Feedback Voltage
(LM2574)
Efficiency
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
0.1A
≤
I
LOAD
≤
0.5A, 7V≤ V
IN
≤
40V, V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 3.3V
0.1A
≤
I
LOAD
≤
0.5A, 4.75V
≤
V
IN
≤
40V,
V
OUT
= 3.3V
V
IN
= 12V, I
LOAD
= 0.1A
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
0.1A
≤
I
LOAD
≤
0.5A, 7V≤ V
IN
≤
40V,
V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
V
IN
= 25V, I
LOAD
= 0.1A, V
OUT
= 12V
0.1A
≤
I
LOAD
≤
0.5A, 15V
≤
V
IN
≤
40V,
V
OUT
= 12V
V
IN
= 25V, I
LOAD
= 0.1A
11.760
11.520
11.400
4.900
4.800
4.750
3.234
3.168
3.135
1.217
1.193
1.180
1.230
1.230
78
1.243
1.267
1.280
V
V
V
%
SYSTEM PARAMETERS, 3.3V REGULATORS
(Note 3) Test Circuit
Figure 3
V
OUT
V
OUT
η
Output Voltage
Output Voltage
(LM2574-3.3)
Efficiency
3.3
3.3
73
3.366
3.432
3.465
V
V
V
%
SYSTEM PARAMETERS, 5V REGULATORS
(Note 3) Test Circuit
Figure 3
V
OUT
V
OUT
η
Output Voltage
Output Voltage
(LM2574-5.0)
Efficiency
5.0
5.0
78
5.100
5.200
5.250
V
V
V
%
SYSTEM PARAMETERS, 12V REGULATORS
(Note 3) Test Circuit
Figure 3
V
OUT
V
OUT
η
Output Voltage
Output Voltage
(LM2574-12)
Efficiency
12
12
88
12.240
12.480
12.600
V
V
V
%
LM2574
2
August 1999
LM2574
Micrel
Electrical Characteristics (continued)
Symbol
Parameter
Condition
Min
Typ
Max
Units
DEVICE PARAMETERS, ADJUSTABLE REGULATOR
I
B
Feedback Bias Current
V
OUT
= 5V
50
100
500
nA
nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
f
o
V
SAT
DC
I
CL
I
L
I
Q
I
STBY
θ
JA
Oscillator Frequency
Saturation Voltage
Max Duty Cycle (ON)
Current Limit
Output Leakage Current
Quiescent Current
Standby Quiescent Current
Thermal Resistance
Note 8
I
OUT
= 0.5A,
Note 4
Note 5
Peak Current, t
ON
≤
3µs,
Note 4
V
IN
,
Note 6,
Output = 0V
Note 6,
Output = –1V
Note 6
ON/OFF Pin = 5V (OFF)
N Package, Junction to Ambient,
Note 7
WM Package, Junction to Ambient,
Note 7
93
0.7
0.65
47
42
52
0.8
98
1.0
1.6
1.8
2
30
10
200
58
63
1.2
1.4
kHz
kHz
V
V
%
A
mA
mA
µA
°C/W
°C/W
7.5
5
50
85
100
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS
Test Circuit
Figures 2, 3
V
IH
V
IL
I
IH
I
IL
Note 1
ON/OFF Input Level
ON/OFF Input Level
ON/OFF Logic Current
ON/OFF Logic Current
V
OUT
= 0V
V
OUT
= 5V
ON/OFF = 5V (OFF)
ON/OFF = 0V (ON)
2.2
2.4
1.4
1.2
4
0.01
1.0
0.8
30
10
V
V
V
V
µA
µA
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate 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 extremes
are guaranteed via testing.
External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When
the LM2574 is used as shown in
Figure 1
test circuit, system performance will be shown in system parameters section of Electrical Character-
istics.
Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input.
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 with approximately 1 square inches of PC board copper surrounding the leads.
Note 2
Note 3
Note 4
Note 5
Note 6
Note 7
August 1999
3
LM2574
LM2574
Micrel
(Circuit of Figure 1)
Typical Performance Characteristics
Supply Current
20
18
SUPPLY CURRENT (mA)
Supply Current
vs. Duty Cycle
STANDBY QUIESCENT CURRENT (µA)
Standby
Quiescent Current
200
VIN = 40V
16
14
12
10
8
6
4
0
10
20
30
SUPPLY CURRENT (mA)
Measured at
Ground Pin
TJ = 25˚C
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 = 100 mA
150
VON/OFF = 5V
VIN = 12V
50
100
ILOAD to 0.5A
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
1.5
VI N = 25V
SATURATION VOLTAGE (V)
OUTPUT CURRENT (A)
Switch
Saturation Voltage
1.1
100
95
0.9
-55˚C
-40˚C
0.7
25˚C
EFFICIENCY (%)
Efficiency
VOUT = 12V
0.5A
100 mA
100 mA
0.5A
VOUT = 3V
90
85
80
75
70
65
60
0
0.1
0.2
0.3
0.4
0.5
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
1
0.5
0.5 125˚C
150˚C
0.3
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 = 100mA
TJ = 25
STANDBY QUIESCENT CURRENT (nA)
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 = 100 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 = 100mA
Normalized to TJ = 25˚C
VOUT = 5V
Normalized at 25˚C
1.5
ILOAD = 0.5A
∆V
OUT = 5%
R IND = 0.2Ω
+4
+2
0
-2
-4
--6
VIN = 40V
1.0
ILOAD = 100 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)
LM2574
4
August 1999
LM2574
Micrel
Typical Performance Characteristics (continued)
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 = 100mA
Normalized to TJ = 25˚C
15
10
5
0
-5
-10
-15
-20
0
20
40
ILOAD = 100 mA
VIN = 40V
VIN = 7V
25 50 75 100 125 150
60
80
100
JUNCTION TEMPERATURE (˚C)
DUTY CYCLE (%)
* Adjustable version only
FB
V
IN
C
IN
22µF
LM2574
(adjustable)
OUT
PWR
SIG ON/
GND
GND OFF
330µH
3.09k
11DQ06
C
OUT
220µF
1k
Load
FB
V
IN
C
IN
22µF
PWR
GND
LM2574–
3.3, 5, 12
OUT
SIG ON/
GND OFF
11DQ06
330µH
C
OUT
220µF
Figure 2. Adjustable Regulator Test Circuit
Figure 3. Fixed Regulator Test Circuit
Block Diagrams
V IN
FEED-
BACK
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
1/2 AMP
SWITCH
FEED-
BACK
+
1.0k
4
+
-
+
-
COMPARATOR
1/2 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
August 1999
5
LM2574
Load
PCB Design
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