July 2005 1 M9999-072805
LM2574 Micrel, Inc.
LM2574
52kHz Simple 0.5A Buck Regulator
General Description
The LM2574 family is a series of easy to use fixed and ad-
justable switching voltage regulators. The LM2574 contains
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 and 5V fixed output ver-
sions, 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.
All support documentation can be found on Micrel’s web site
at www.micrel.com.
Typical Application
VIN
PWR
GND SIG
GND ON/
OFF
OUT
FB
LM2574
CIN
22µF
40V MAX
UNREGULATED
DC IN
REGULATED
OUTPUT
0.5A
11DQ05 COUT
220µF
330µH
Figure 1. Fixed Output Regulator Circuit
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)
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
LM2574 Micrel, Inc.
M9999-072805 2 July 2005
Pin Configuration
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8 NC
7 OUTPUT
6 NC
5 VIN
8-Pin DIP (N)
Ordering Information
Part Number Junction
Temp. Range
Package
Standard Pb-Free
LM2574BN LM2574YN –40ºC to +85ºC 8-pin Plastic DIP
LM2574-3.3BN LM2574-3.3YN –40ºC to +85ºC 8-pin Plastic DIP
LM2574-5.0BN LM2574-5.0YN –40ºC to +85ºC 8-pin Plastic DIP
July 2005 3 M9999-072805
LM2574 Micrel, Inc.
Absolute Maximum Ratings(1)
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 (TS) ............. –65°C to +150°C
Minimum ESD Rating
C = 100pF, R = 1.5kΩ ................................................ 2kV
FB Pin ........................................................................ 1kV
Lead Temperature (soldering, 10 sec.) ...................... 260°C
Operating Ratings(1)
Supply Voltage
LM2574 ...................................................................... 40V
Temperature Range
LM2574 ...........................................–40°C ≤ TJ ≤ +125°C
Maximum Junction Temperature (TJ .......................... 150°C
Electrical Characteristics(2)
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(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, 1.193 1.230 1.267 V
(LM2574) VOUT = 5V 1.180 1.280 V
η Efficiency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %
System Parameters, 3.3V Regulators(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
η Efficiency VIN = 12V, ILOAD = 0.1A 73 %
System Parameters, 5V Regulators(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
η Efficiency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 %
Notes:
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 “Electrical Charac-
teristics.”
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.
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 Charac-
teristics.”
LM2574 Micrel, Inc.
M9999-072805 4 July 2005
Electrical Characteristics
Symbol Parameter Condition Min Typ Max Units
Device Parameters, Adjustable Regulator
IB Feedback Bias Current VOUT = 5V 50 100 nA
500 nA
Device Parameters, Fixed and Adjustable Regulators
fo Oscillator Frequency Note 8 47 52 58 kHz
42 63 kHz
VSAT Saturation Voltage IOUT = 0.5A(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(4) 0.7 1.0 1.6 A
0.65 1.8
IL Output Leakage Current VIN, Note 6, Output = 0V 2 mA
Note 6, Output = –1V 7.5 30
IQ Quiescent Current Note 6 5 10 mA
ISTBY Standby Quiescent Current ON/OFF Pin = 5V (OFF) 50 200 µA
θJA Thermal Resistance N Package, Junction to Ambient(7) 85 °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
Notes:
4. Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input.
5. Feedback (pin 4) removed from output and connected to 0V.
6. Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.
7. Junction-to-ambient thermal resistance with approximately 1 square inches of PC board copper surrounding the leads.
Test Circuit
VIN
PWR
GND SIG
GND ON/
OFF
OUT
FB
LM2574
(adjustable)
CIN
22µF
11DQ06 COUT
220µF
330µH
3.09k
1k
Figure 2. Adjustable Regulator Test Circuit
VIN
P W R
GND SIG
GND ON/
OFF
OUT
FB
LM2574–
3.3, 5, 12
CIN
22µF
11DQ06 COUT
220µF
330µH
Figure 3. Fixed Regulator Test Circuit
July 2005 5 M9999-072805
LM2574 Micrel, Inc.
Typical Characteristics (Circuit of Figure 1)
Supply Current
INPUT VOL TA GE ( V )
20 Measured at
Grou nd Pin
TJ = 25˚C
VOUT = 5V
18
16
14
12
10
8
6
40 10 20 30 40 50 60
IL O AD
to 0.5A
Supply Current
vs. Duty Cycle
D U T Y C YC LE ( % )
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
00 20 40 60 80 100
VIN from 7V to 40V
IL O AD
= 100 mA
JU N C T I O N TEM PE R ATU R E ( ˚C )
200
150
100
50
0
-75
VIN = 12V
Standby
Quiescent Current
VIN = 40V
-50 -25 0 25 50 75 100 125150
Current Limit
JU N C T I O N TEM PE R ATU R E ( ˚C )
1.5
1
0.5
0
-75
VIN = 25V
INPUT VOL TA GE ( V )
100
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
JU N C T I O N TEM PE R ATU R E ( ˚C )
5.0
IL O AD
= 100 mA
Line Regulation
INPUT VOL TA GE ( V )
14
0
JU N C T I O N TEM PE R ATU R E ( ˚C )
100
-100
-75
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
5 10 15 20 25 30
75
50
25
0
-25
-50
-75
JU N C T I O N TEM PE R ATU R E ( ˚C )
+8
-8
-75
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 toVIN = 10V
VOUT = 5V
IL O AD
= 100mA
TJ = 25
VON/OFF
= 5V
Switch
Saturation Voltage
SW I TC H C U R R EN T ( A)
1.1
-55˚C
0.9
0.7
0.5
0.3
0 0.1 0.2 0.3 0.4 0.5
25˚C
125˚C
150˚C
-40˚C
Dropout Voltage
JU N C T I O N TEM PE R ATU R E ( ˚C )
2.0
-75 -50 -25 0 25 50 75 100125150
∆VOUT = 5%
RIND = 0.2Ω
IL O AD
= 0.5A
IL O AD
= 100 mA
1.5
1.0
0.5
0
Normalized
Output Voltage
JU N C T I O N TEM PE R ATU R E ( ˚C )
100
75
50
25
0
-25
-50
-75
-100
-75 -50 -25 0 25 50 75 100125150
VIN = 12V
IL O AD
= 100mA
Normalized toT
J = 25 ˚C
VOUT = 5V
LM2574 Micrel, Inc.
M9999-072805 6 July 2005
Typical Performance Characteristics (continued)
Normalized
Feedback Voltage*
JU N C T I O N TEM PE R ATU R E ( ˚C )
25
20
15
10
5
0
-5
-10
-15
-20
-25
-75 -50 -25 0 25 50 75 100125150
VIN = 12V
IL O AD
= 100mA
Normalized toT
J= 25˚C
Feedback Voltage
vs Duty Cycle*
D U T Y C YC LE ( % )
20
15
10
5
0
-5
-10
-15
-20
IL O AD
= 100 mA
VIN = 40V
VIN = 7V
0 20 40 60 80 100
* Adjustable version only
July 2005 7 M9999-072805
LM2574 Micrel, Inc.
ON/OFF
C OM P AR AT OR
FIXED G A I N
E R R O R A M P
1/2 AMP
SWITCH
OUTPUT
DRIVER
+
-
+
-
VIN
F EED -
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
C OM P AR AT OR
FIXED G A I N
E R R O R A M P
1/2 AMP
SWITCH
OUTPUT
DRIVER
+
-
+
-
VIN
F EED -
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
LM2574 Micrel, Inc.
M9999-072805 8 July 2005
Package Information
0.380 (9.65)
0.370 (9.40) 0.135 (3.43)
0.125 (3.18)
PIN 1
DIMENSIONS:
INCH (MM)
0.018 (0.57)
0.100 (2.54)
0.013 (0.330)
0.010 (0.254)
0.300 (7.62)
0.255 (6.48)
0.245 (6.22)
0.380 (9.65)
0.320 (8.13)
0.0375 (0.952)
0.130 (3.30)
8-Pin DIP (N)
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB 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.
© 2003 Micrel, Inc.