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.
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)
Typical Application
40V MAX
UNREGULATED
DC IN
C
IN
22µF
V
IN
LM2574
PWR
GND
FB
330µH
OUT
SIG ON/
GND OFF
REGULATED
OUTPUT
0.5A
C
OU T
220µF
11DQ05
Figure 1. Fixed Output Regulator Circuit
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2005
1
M9999-072805
LM2574
Micrel, Inc.
Ordering Information
Part Number
Standard
LM2574BN
LM2574-3.3BN
LM2574-5.0BN
Pb-Free
LM2574YN
LM2574-3.3YN
LM2574-5.0YN
Junction
Temp. Range
–40ºC to +85ºC
–40ºC to +85ºC
–40ºC to +85ºC
Package
8-pin Plastic DIP
8-pin Plastic DIP
8-pin Plastic DIP
Pin Configuration
FB 1
SIG GND 2
ON/OFF 3
PWR GND 4
8-Pin DIP (N)
8 NC
7 OUTPUT
6 NC
5 VIN
M9999-072805
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July 2005
LM2574
Micrel, Inc.
Absolute Maximum Ratings
(1)
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 (T
S
) ............. –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 ≤ T
J
≤ +125°C
Maximum Junction Temperature (T
J
.......................... 150°C
Electrical Characteristics
(2)
Symbol
V
OUT
V
OUT
η
V
OUT
V
OUT
η
V
OUT
V
OUT
η
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.”
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.
Parameter
Condition
Min
Typ
Max
Units
V
V
V
%
System Parameters, Adjustable Regulators
(3)
, Test Circuit
Figure 2
Feedback Voltage
Feedback Voltage
(LM2574)
Efficiency
Regulators
(3)
,
Output Voltage
Output Voltage
(LM2574-3.3)
Efficiency
Output Voltage
Output Voltage
(LM2574-5.0)
Efficiency
0.1A ≤ I
LOAD
≤ 0.5A, 7V≤ V
IN
≤ 40V,
V
OUT
= 5V
Test Circuit
Figure 3
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
V
IN
= 12V, I
LOAD
= 0.1A, V
OUT
= 5V
1.217
1.193
1.180
1.230
1.230
78
3.234
3.168
3.135
3.3
3.3
73
4.900
4.800
4.750
5.0
5.0
78
5.100
5.200
5.250
3.366
3.432
3.465
1.243
1.267
1.280
System Parameters, 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
= 3.3V
V
V
V
%
V
V
V
%
System Parameters, 5V Regulators
(3)
, Test Circuit
Figure 3
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
= 5V
July 2005
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M9999-072805
LM2574
Micrel, Inc.
Parameter
Feedback Bias Current
Condition
V
OUT
= 5V
Min
Typ
50
Max
100
500
58
63
1.2
1.4
1.6
1.8
2
30
10
200
Units
nA
nA
kHz
kHz
V
V
%
A
mA
mA
µA
°C/W
V
V
1.0
0.8
30
10
V
V
µA
µA
Electrical Characteristics
Symbol
I
B
Device Parameters, Adjustable Regulator
Device Parameters, Fixed and Adjustable Regulators
f
o
V
SAT
DC
I
CL
I
L
I
Q
Oscillator Frequency
Saturation Voltage
Max Duty Cycle (ON)
Current Limit
Output Leakage Current
Quiescent Current
Standby Quiescent Current
Thermal Resistance
ON/OFF Input Level
ON/OFF Input Level
ON/OFF Logic Current
ON/OFF Logic Current
Note 8
I
OUT
= 0.5A
(4)
Note 5
Peak Current, t
ON
≤ 3µs
(4)
V
IN
,
Note 6,
Output = 0V
Note 6,
Output = –1V
Note 6
ON/OFF Pin = 5V (OFF)
N Package, Junction to Ambient
(7)
V
OUT
= 0V
V
OUT
= 5V
ON/OFF = 5V (OFF)
ON/OFF = 0V (ON)
2.2
2.4
93
0.7
0.65
47
42
52
0.8
98
1.0
7.5
5
50
85
1.4
1.2
4
0.01
I
STBY
θ
JA
On/Off Control, Fixed and Adjustable Regulators
Test Circuit
Figures 2, 3
V
IH
V
IL
I
IH
I
IL
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
V
IN
FB
C
IN
22µF
LM2574
(adjustable)
OUT
PWR
SI
G
ON/
GND GND OFF
330µH
11DQ06
C
OU T
220µF
3.09k
1k
Figure 2. Adjustable Regulator Test Circuit
FB
C
IN
22µF
LM2574–
3.3, 5, 12
OUT
P W R S I G ON/
GND GND O F F
V
IN
330µH
11DQ06
C
OU T
220µF
Figure 3. Fixed Regulator Test Circuit
M9999-072805
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July 2005
LM2574
Micrel, Inc.
Typical Characteristics
(Circuit of Figure 1)
Supply Current
20
Supply Current
vs. Duty Cycle
20.0
17.5
15.0
12.5
10.0
7.5
Standby
Quiescent Current
200
150
18
16
14
12
10
8
6
4
0
10
20
30
Measured at
Ground Pin
TJ = 25˚C
VOUT = 5V
VIN = 40V
100
I LO AD = 100 mA
VON/OFF = 5V
VIN = 12V
I LO AD to 0.5A
5.0
2.5
50
VIN from 7V to 40V
0
20
40
60
80
100
40
50
60
0
0
-75
-50 -25 0 25 50 75 100 125150
JU N C TI O N TEM PER ATU R E ( ˚ C )
INPUT VOLTAGE ( V)
D U TY C YC LE ( % )
Current Limit
1.5
Switch
Saturation Voltage
1.1
100
Efficiency
95
VOUT = 12V
V IN = 25V
0.9
1
90
0.5A
100 mA
100 mA
-55˚C
-40˚C
0.7
85
80
75
70
65
25˚C
0.5
0.5A
VOUT = 3V
0.5
125˚C
150˚C
0.3
0
0
-75
-50 -25 0 25 50 75 100125 150
JU N C TI O N TEM PER ATU R E ( ˚ C )
0.1
0.2
0.3
0.4
0.5
60
0
5
10 15 20 25 30
35 40
SW I TC H C U R R EN T ( A)
INPUT VOLTAGE ( V)
Minimum Operating
Voltage
5.0
4.5
Line Regulation
14
12
Feedback Pin Current
100
4.0
3.5
3.0
2.5
2.0
1.5
1.0
VOUT = 1.23V
I LO AD = 100 mA
10
8
6
4
2
0
-2
-4
-6
0
Normalized toVIN = 10V
VOUT = 5V
ILO AD = 100mA
TJ = 25
75
50
25
0
-25
-50
-75
0.5
0
-75 -50 -25 0 25 50 75 100125150
J U N C TI O N TEM PER ATU R E ( ˚ C )
5
10
15
20
25
INPUT VOLTAGE ( V)
30
-100
-75
-50 -25 0 25 50 75 100 125150
JU N C TI O N TEM PER ATU R E ( ˚ C )
100
Normalized
Output Voltage
VIN = 12V
I LO AD = 100mA
Normalized toTJ = 25˚C
VOUT = 5V
Oscillator Frequency
+8
75
+6
+4
+2
0
-2
-4
--6
Normalized at 25˚ C
2.0
Dropout Voltage
I LO AD = 0.5A
∆VOUT = 5%
R IND = 0.2Ω
50
1.5
25
0
1.0
VIN = 40V
-25
-50
0.5
I LO AD = 100 mA
-75
-100
-75 -50 -25 0
25 50 75 100125150
VIN = 12V
-8
-75
-50 -25 0 25 50 75 100125150
JU N C TI O N TEM PER ATU R E ( ˚ C )
0
-75 -50 -25 0 25 50 75 100125150
JU N C TI O N TEM PER ATU R E ( ˚ C )
J U N C TI O N TEM PER ATU R E ( ˚ C )
July 2005
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M9999-072805
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