August 1999
1
LM2574
LM2574
Micrel
Ordering Information
Part Number
Temp. Range
Package
LM2574BN
40
C to +85
C
8-pin Plastic DIP
LM2574BWM
40
C to +85
C
14-pin Wide SOIC
LM2574-3.3BN
40
C to +85
C
8-pin Plastic DIP
LM2574-3.3BWM
40
C to +85
C
14-pin Wide SOIC
LM2574-5.0BN
40
C to +85
C
8-pin Plastic DIP
LM2574-5.0BWM
40
C to +85
C
14-pin Wide SOIC
LM2574-12BN
40
C to +85
C
8-pin Plastic DIP
LM2574-12BWM
40
C to +85
C
14-pin Wide SOIC
LM2574
52kHz Simple 0.5A Buck Regulator
Final Information
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 < 200
A 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)
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 200
A.
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.
Pin Configuration
8-pin DIP (N)
FB
1
SIG GND
2
ON/OFF
3
PWR GND
4
8
*
7
OUTPUT
6
*
5
V
IN
14-pin SOIC (WM)
*
1
*
2
FB
3
SIG GND
4
ON/OFF
5
PWR GND
6
*
7
14
*
13
*
12
OUTPUT
11
*
10
V
IN
9
*
8
*
* NC: solder to printed circuit for
maximum heat transfer
Figure 1. Fixed Output Regulator Circuit
V
IN
PWR
GND
SIG
GND
ON/
OFF
OUT
FB
LM2574
C
IN
22F
40V MAX
UNREGULATED
DC IN
REGULATED
OUTPUT
0.5A
11DQ05
C
OUT
220F
330H
Typical Application
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
LM2574
Micrel
LM2574
2
August 1999
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 = 1.5k
............................................... 2kV
FB Pin ....................................................................... 1kV
Lead Temperature (soldering, 10 sec.) ..................... 260
C
Maximum Junction Temperature ............................... 150
C
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
= 100mA.
Symbol
Parameter
Condition
Min
Typ
Max
Units
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit
Figure 2
V
OUT
Feedback Voltage
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
1.217
1.230
1.243
V
V
OUT
Feedback Voltage
0.1A
I
LOAD
0.5A, 7V
V
IN
40V, V
OUT
= 5V
1.193
1.230
1.267
V
(LM2574)
1.180
1.280
V
Efficiency
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
78
%
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit
Figure 3
V
OUT
Output Voltage
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 3.3V
3.234
3.3
3.366
V
V
OUT
Output Voltage
0.1A
I
LOAD
0.5A, 4.75V
V
IN
40V,
3.168
3.3
3.432
V
(LM2574-3.3)
V
OUT
= 3.3V
3.135
3.465
V
Efficiency
V
IN
= 12V, I
LOAD
= 0.1A
73
%
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit
Figure 3
V
OUT
Output Voltage
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
4.900
5.0
5.100
V
V
OUT
Output Voltage
0.1A
I
LOAD
0.5A, 7V
V
IN
40V,
4.800
5.0
5.200
V
(LM2574-5.0)
V
OUT
= 5V
4.750
5.250
V
Efficiency
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
78
%
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit
Figure 3
V
OUT
Output Voltage
V
IN
= 25V, I
LOAD
= 0.1A, V
OUT
= 12V
11.760
12
12.240
V
V
OUT
Output Voltage
0.1A
I
LOAD
0.5A, 15V
V
IN
40V,
11.520
12
12.480
V
(LM2574-12)
V
OUT
= 12V
11.400
12.600
V
Efficiency
V
IN
= 25V, I
LOAD
= 0.1A
88
%
Operating Ratings
Temperature Range
LM2574 ........................................... 40
C
T
J
+125
C
Supply Voltage
LM2574 ..................................................................... 40V
August 1999
3
LM2574
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
nA
500
nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
f
o
Oscillator Frequency
Note 8
47
52
58
kHz
42
63
kHz
V
SAT
Saturation Voltage
I
OUT
= 0.5A, Note 4
0.8
1.2
V
1.4
V
DC
Max Duty Cycle (ON)
Note 5
93
98
%
I
CL
Current Limit
Peak Current, t
ON
3
s, Note 4
0.7
1.0
1.6
A
0.65
1.8
I
L
Output Leakage Current
V
IN
, Note 6, Output = 0V
2
mA
Note 6, Output = 1V
7.5
30
I
Q
Quiescent Current
Note 6
5
10
mA
I
STBY
Standby Quiescent Current
ON/OFF Pin = 5V (OFF)
50
200
A
JA
Thermal Resistance
N Package, Junction to Ambient, Note 7
85
C/W
WM Package, Junction to Ambient, Note 7
100
C/W
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit
Figures 2, 3
V
IH
ON/OFF Input Level
V
OUT
= 0V
2.2
1.4
V
2.4
V
V
IL
ON/OFF Input Level
V
OUT
= 5V
1.2
1.0
V
0.8
V
I
IH
ON/OFF Logic Current
ON/OFF = 5V (OFF)
4
30
A
I
IL
ON/OFF Logic Current
ON/OFF = 0V (ON)
0.01
10
A
Note 1
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.
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 extremes 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 LM2574 is used as shown in
Figure 1 test circuit, system performance will be shown in system parameters section of Electrical Character-
istics.
Note 4
Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input.
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 with approximately 1 square inches of PC board copper surrounding the leads.
LM2574
Micrel
LM2574
4
August 1999
Typical Performance Characteristics
(Circuit of Figure 1)
Supply Current
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
20
Measured at
Ground Pin
TJ = 25C
VOUT = 5V
18
16
14
12
10
8
6
4
0
10
20
30
40
50
60
ILOAD to 0.5A
Supply Current
vs. Duty Cycle
DUTY CYCLE (%)
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0
0
20
40
60
80
100
VIN from 7V to 40V
ILOAD = 100 mA
SUPPLY CURRENT (mA)
JUNCTION TEMPERATURE (C)
200
150
100
50
0
-75
VIN = 12V
STANDBY QUIESCENT CURRENT (A)
Standby
Quiescent Current
VIN = 40V
-50 -25
0 25 50 75 100 125 150
Current Limit
JUNCTION TEMPERATURE (C)
1.5
1
0.5
0
-75
VIN = 25V
OUTPUT CURRENT (A)
INPUT VOLTAGE (V)
100
EFFICIENCY (%)
Efficiency
VOUT = 12V
-50 -25
0 25 50 75 100 125 150
95
90
85
80
75
70
65
60
100 mA
100 mA
VOUT = 3V
0.5A
0.5A
0
5
10 15 20 25 30
35 40
Minimum Operating
Voltage
JUNCTION TEMPERATURE (C)
5.0
ILOAD = 100 mA
INPUT VOLTAGE (V)
Line Regulation
INPUT VOLTAGE (V)
14
0
NORMALIZED FEEDBACK VOLTAGE (mV)
JUNCTION TEMPERATURE (C)
100
-100
-75
STANDBY QUIESCENT CURRENT (nA)
Feedback Pin Current
-50 -25 0
25 50 75 100 125 150
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 75 100 125 150
12
10
8
6
4
2
0
-2
-4
-6
5
10
15
20
25
30
75
50
25
0
-25
-50
-75
JUNCTION TEMPERATURE (C)
+8
-8
-75
NORMALIZED FREQUENCY (%)
Oscillator Frequency
-50 -25
0 25 50 75 100 125 150
+6
+4
+2
0
-2
-4
--6
VIN = 12V
VIN = 40V
Normalized at 25C
Normalized to VIN = 10V
VOUT = 5V
ILOAD = 100mA
TJ = 25
VON/OFF = 5V
Switch
Saturation Voltage
SWITCH CURRENT (A)
1.1
-55C
0.9
0.7
0.5
0.3
0
SATURATION VOLTAGE (V)
0.1
0.2
0.3
0.4
0.5
25C
125C
150C
-40C
Dropout Voltage
JUNCTION TEMPERATURE (C)
INPUT-OUTPUT DIFFERENTIAL (V)
2.0
-75 -50 -25
0 25 50 75 100 125 150
VOUT = 5%
RIND = 0.2
ILOAD = 0.5A
ILOAD = 100 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 75 100 125 150
VIN = 12V
ILOAD = 100mA
Normalized to TJ = 25C
VOUT = 5V
August 1999
5
LM2574
LM2574
Micrel
Typical Performance Characteristics (continued)
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 75 100 125 150
VIN = 12V
ILOAD = 100mA
Normalized to TJ = 25C
Feedback Voltage
vs Duty Cycle*
DUTY CYCLE (%)
FEEDBACK VOLTAGE CHANGE (mV)
20
15
10
5
0
-5
-10
-15
-20
ILOAD = 100 mA
VIN = 40V
VIN = 7V
0
20
40
60
80
100
* Adjustable version only
ON/OFF
COMPARATOR
FIXED GAIN
ERROR AMP
1/2 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
1/2 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
Fixed Regulator
Adjustable Regulator
V
IN
PWR
GND
SIG
GND
ON/
OFF
OUT
FB
LM2574
(adjustable)
C
IN
22F
11DQ06
C
OUT
220F
330H
3.09k
1k
Load
V
IN
PWR
GND
SIG
GND
ON/
OFF
OUT
FB
LM2574
3.3, 5, 12
C
IN
22F
11DQ06
C
OUT
220F
330H
Load
Figure 3. Fixed Regulator Test Circuit
Figure 2. Adjustable Regulator Test Circuit
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