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
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)
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.
Pin Configuration
8-pin DIP (N)
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8*
7 OUTPUT
6*
5V
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
22µF
40V MAX
UNREGULATED
DC IN REGULATED
OUTPUT
0.5A
11DQ05 C
OUT
220µF
330µH
Typical Application
LM2574 Micrel
LM2574 2 August 1999
Absolute Maximum Ratings
Maximum Supply Voltage
LM2574 .....................................................................45V
OFF Pin Input Voltage................................ –0.3V ≤ V ≤ VIN
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
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 = 100mA.
Symbol Parameter Condition Min Typ Max Units
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit
Figure 2
VOUT Feedback Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 5V 1.217 1.230 1.243 V
VOUT Feedback Voltage 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, VOUT = 5V 1.193 1.230 1.267 V
(LM2574) 1.180 1.280 V
ηEfficiency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit
Figure 3
VOUT Output Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 3.3V 3.234 3.3 3.366 V
VOUT Output Voltage 0.1A ≤ ILOAD ≤ 0.5A, 4.75V ≤ VIN ≤ 40V, 3.168 3.3 3.432 V
(LM2574-3.3) VOUT = 3.3V 3.135 3.465 V
ηEfficiency VIN = 12V, ILOAD = 0.1A 73 %
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit
Figure 3
VOUT Output Voltage VIN = 12V, ILOAD = 0.1A, VOUT = 5V 4.900 5.0 5.100 V
VOUT Output Voltage 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, 4.800 5.0 5.200 V
(LM2574-5.0) VOUT = 5V 4.750 5.250 V
ηEfficiency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit
Figure 3
VOUT Output Voltage VIN = 25V, ILOAD = 0.1A, VOUT = 12V 11.760 12 12.240 V
VOUT Output Voltage 0.1A ≤ ILOAD ≤ 0.5A, 15V ≤ VIN ≤ 40V, 11.520 12 12.480 V
(LM2574-12) VOUT = 12V 11.400 12.600 V
ηEfficiency VIN = 25V, ILOAD = 0.1A 88 %
Operating Ratings
Temperature Range
LM2574 ........................................... 40°C ≤ TJ ≤ +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
IBFeedback Bias Current VOUT = 5V 50 100 nA
500 nA
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
foOscillator Frequency Note 8 47 52 58 kHz
42 63 kHz
VSAT Saturation Voltage IOUT = 0.5A, Note 4 0.8 1.2 V
1.4 V
DC Max Duty Cycle (ON) Note 5 93 98 %
ICL Current Limit Peak Current, tON ≤ 3µs, Note 4 0.7 1.0 1.6 A
0.65 1.8
ILOutput Leakage Current VIN, Note 6, Output = 0V 2 mA
Note 6, Output = –1V 7.5 30
IQQuiescent Current Note 6 510mA
ISTBY Standby Quiescent Current ON/OFF Pin = 5V (OFF) 50 200 µA
θJA 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
VIH ON/OFF Input Level VOUT = 0V 2.2 1.4 V
2.4 V
VIL ON/OFF Input Level VOUT = 5V 1.2 1.0 V
0.8 V
IIH ON/OFF Logic Current ON/OFF = 5V (OFF) 4 30 µA
IIL ON/OFF Logic Current ON/OFF = 0V (ON) 0.01 10 µA
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 = 25˚C
VOUT = 5V
18
16
14
12
10
8
6
40102030405060
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
00 2040 6080100
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 (µA)
Standby
Quiescent Current
VIN = 40V
-50 -25 0 25 50 75 100 125150
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 100125 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 125150
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 100125150
12
10
8
6
4
2
0
-2
-4
-6 51015202530
75
50
25
0
-25
-50
-75
JUNCTION TEMPERATURE (˚C)
+8
-8
-75
NORMALIZED FREQUENCY (%)
Oscillator Frequency
-50 -25 0 25 50 75 100125150
+6
+4
+2
0
-2
-4
--6 VIN = 12V
VIN = 40V
Normalized at 25˚C
Normalized to VIN = 10V
VOUT = 5V
ILOAD = 100mA
TJ = 25
VON/OFF = 5V
Switch
Saturation Voltage
SWITCH CURRENT (A)
1.1
-55˚C
0.9
0.7
0.5
0.3 0
SATURATION VOLTAGE (V)
0.1 0.2 0.3 0.4 0.5
25˚C
125˚C
150˚C
-40˚C
Dropout Voltage
JUNCTION TEMPERATURE (˚C)
INPUT-OUTPUT DIFFERENTIAL (V)
2.0
-75 -50 -25 0 25 50 75 100125150
∆VOUT = 5%
RIND = 0.2Ω
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 100125150
VIN = 12V
ILOAD = 100mA
Normalized to TJ = 25˚C
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 100125150
VIN = 12V
ILOAD = 100mA
Normalized to TJ = 25˚C
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
020 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
22µF
11DQ06 C
OUT
220µF
330µH
3.09k
1k
Load
V
IN
PWR
GND SIG
GND ON/
OFF
OUT
FB
LM2574–
3.3, 5, 12
C
IN
22µF
11DQ06 C
OUT
220µF
330µH
Load
Figure 3. Fixed Regulator Test CircuitFigure 2. Adjustable Regulator Test Circuit
