LM2575
1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
FEATURES
•
Fixed 3.3-V, 5-V, 12-V, and 15-V Options With
±5%
Regulation (Max) Over Line, Load, and
Temperature Conditions
Adjustable Option With a Range of 1.23 V to
37 V and
±4%
Regulation (Max) Over Line,
Load, and Temperature Conditions
Specified 1-A Output Current
Wide Input Voltage Range…4.75 V to 40 V
Requires Only Four External Components
(Fixed Versions) and Uses Readily Available
Standard Inductors
52-kHz (Typ) Fixed-Frequency Internal
Oscillator
TTL Shutdown Capability With 50-µA (Typ)
Standby Current
High Efficiency…as High as 88% (Typ)
Thermal Shutdown and Current-Limit
Protection With Cycle-by-Cycle Current
Limiting
•
•
•
•
•
•
•
•
APPLICATIONS
•
•
•
•
Simple High-Efficiency Step-Down (Buck)
Regulator
Pre-Regulator for Linear Regulators
On-Card Switching Regulators
Positive-to-Negative Converter (Buck-Boost)
DESCRIPTION/ORDERING INFORMATION
The LM2575 greatly simplifies the design of switching power supplies by conveniently providing all the active
functions needed for a step-down (buck) switching regulator in an integrated circuit. Accepting a wide input
voltage range and available in fixed output voltages of 3.3 V, 5 V, 12 V, 15 V, or an adjustable output version,
the LM2575 has an integrated switch capable of delivering 1 A of load current, with excellent line and load
regulation. The device also offers internal frequency compensation, a fixed-frequency oscillator, cycle-by-cycle
current limiting, and thermal shutdown. In addition, a manual shutdown is available via an external ON/OFF pin.
The LM2575 represents a superior alternative to popular three-terminal linear regulators. Due to its high
efficiency, it significantly reduces the size of the heat sink and, in many cases, no heat sink is required.
Optimized for use with standard series of inductors available from several different manufacturers, the LM2575
greatly simplifies the design of switch-mode power supplies by requiring a minimal addition of only four to six
external components for operation.
The LM2575 is characterized for operation over the virtual junction temperature range of 0
°C
to 85
°C.
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LM2575
FUNCTIONAL BLOCK DIAGRAM
V
IN
1
+
C
IN
Unregulated
DC Input
Internal
Regulator
On/Off
ON/OFF
5
FEEDBACK
4
R2
Fixed-Gain
Error Amp
+
_
R1
1 kW
Comparator
+
_
Driver
1-A
Switch
OUTPUT
2
D1
L1
+
C
OUT
L
O
A
D
V
OUT
1.23-V
Band-Gap
Reference
GND
52-kHz
Oscillator
Reset
Thermal
Shutdown
Current
Limit
3
3.3 V: R2 = 1.7 kW
5 V: R2 = 3.1 kW
12 V: R2 = 8.84 kW
15 V: R2 = 11.3 kW
ADJ: R1 = Open, R2 = 0
Ω
A.
Pin numbers are for the KTT (TO-263) package.
FEEDBACK
4
7-V to 40-V
Unregulated
DC Input
+V
IN
1
3
+
C
IN
100
µF
GND
5
LM2575-05
OUTPUT
2
ON/OFF
D1
1N5819
+
C
OUT
330
µF
C1
100
µF
+
L1
330
µH
L2
20
µH
5-V
Regulated
Output
1-A Load
Optional Output Ripple Filter
A.
Pin numbers are for the KTT (TO-263) package.
Figure 1. Typical Application Circuit (Fixed Version)
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LM2575
Absolute Maximum Ratings
(1)
over operating free-air temperature range (unless otherwise noted)
MIN
V
IN
Supply voltage
ON/OFF pin input voltage
Output voltage to GND (steady state)
T
J
T
stg
(1)
Maximum junction temperature
Storage temperature range
–65
–0.3
MAX
42
V
IN
–1
150
150
UNIT
V
V
V
°C
°C
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating
conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Package Thermal Data
(1)
PACKAGE
PDIP (N)
TO-263 (KTT)
(1)
BOARD
High K, JESD 51-7
High K, JESD 51-5
θ
JC
51°C/W
TBD
θ
JCB
θ
JA
67°C/W
TBD
Maximum power dissipation is a function of T
J
(max),
θ
JA
, and T
A
. The maximum allowable power dissipation at any allowable ambient
temperature is P
D
= (T
J
(max) – T
A
)/θ
JA
. Operating at the absolute maximum T
J
of 150°C can affect reliability.
Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
V
IN
T
J
Supply voltage
Operating virtual junction temperature
4.75
0
MAX
40
85
UNIT
V
°C
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LM2575
Electrical Characteristics
I
LOAD
= 200 mA, V
IN
= 12 V for 3.3-V, 5-V, and adjustable versions, V
IN
= 25 V for 12-V version, V
IN
= 30 V for 15-V version
(unless otherwise noted) (see
Figure 2)
PARAMETER
LM2575-33
TEST CONDITIONS
V
IN
= 12 V, I
LOAD
= 0.2 A
4.75 V
≤
V
IN
≤
40 V,
0.2 A
≤
I
LOAD
≤
1 A
V
IN
= 12 V, I
LOAD
= 0.2 A
LM2575-05
V
OUT
Output voltage
LM2575-12
8 V
≤
V
IN
≤
40 V,
0.2 A
≤
I
LOAD
≤
1 A
V
IN
= 25 V, I
LOAD
= 0.2 A
15 V
≤
V
IN
≤
40 V,
0.2 A
≤
I
LOAD
≤
1 A
V
IN
= 30 V, I
LOAD
= 0.2 A
LM2575-15
18 V
≤
V
IN
≤
40 V,
0.2 A
≤
I
LOAD
≤
1 A
V
IN
= 12 V, V
OUT
= 5 V,
I
LOAD
= 0.2 A
8 V
≤
V
IN
≤
40 V, V
OUT
= 5 V,
0.2 A
≤
I
LOAD
≤
1 A
V
IN
= 12 V, I
LOAD
= 1 A
V
IN
= 12 V, I
LOAD
= 1 A
V
IN
= 15 V, I
LOAD
= 1 A
V
IN
= 18 V, I
LOAD
= 1 A
V
IN
= 12 V, V
OUT
= 5 V,
I
LOAD
= 1 A
V
OUT
= 5 V (ADJ version only)
(1)
T
J
25°C
25°C
Full range
25°C
25°C
Full range
25°C
25°C
Full range
25°C
25°C
Full range
25°C
25°C
Full range
MIN
3.234
3.168
3.135
4.9
4.8
4.75
11.76
11.52
11.4
14.7
14.4
14.25
1.217
1.193
1.18
TYP
3.3
3.3
5
5
12
12
15
15
15
1.23
1.23
75
77
88
88
77
MAX
3.366
3.432
3.465
5.1
5.2
5.25
12.24
12.48
12.6
15.3
15.6
15.75
1.243
1.267
1.28
UNIT
V
Feedback voltage
LM2575-ADJ
V
LM2575-33
LM2575-05
η
Efficiency
LM2575-12
LM2575-15
LM2575-ADJ
I
IB
f
o
V
SAT
Feedback bias current
Oscillator frequency
Saturation voltage
Maximum duty cycle
I
CL
I
L
I
Q
I
STBY
V
IH
ON/OFF logic input level
V
IL
I
IH
I
IL
(1)
(2)
(3)
(4)
ON/OFF input current
Peak current
Output leakage current
Quiescent current
Standby quiescent current
25°C
%
25°C
Full range
25°C
Full range
25°C
Full range
25°C
25°C
Full range
93
1.7
1.3
47
42
50
52
0.9
98
2.8
100
500
58
63
1.2
1.4
3.6
4
2
nA
kHz
V
%
A
mA
mA
µA
I
OUT
= 1 A
(2)
(3)
(1) (2)
V
IN
= 40
(4)
, Output = 0 V
V
IN
=
(4)
40
(4)
,
Output = –1 V
25°C
25°C
25°C
25°C
Full range
25°C
Full range
25°C
2.2
2.4
7.5
5
50
1.4
1.2
12
0
30
10
200
OFF (ON/OFF pin = 5 V)
OFF (V
OUT
= 0 V)
ON (V
OUT
= nominal voltage)
OFF (ON/OFF pin = 5 V)
OFF (ON/OFF pin = 0 V)
1
0.8
30
10
V
µA
In the event of an output short or an overload condition, self-protection features lower the oscillator frequency to
∼18
kHz and the
minimum duty cycle from 5% to
∼2%.
The resulting output voltage drops to
∼40%
of its nominal value, causing the average power
dissipated by the IC to lower.
Output is not connected to diode, inductor, or capacitor. Output is sourcing current.
Feedback is disconnected from output and connected to 0 V.
To force the output transistor off, FEEDBACK is disconnected from output and connected to 12 V for the adjustable, 3.3-V, and 5-V
versions; and 25 V for the 12-V and 15-V versions.
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LM2575
APPLICATION INFORMATION
Layout Guidelines
With any switching regulator, circuit layout plays an important role in circuit performance. Wiring and parasitic
inductances, as well as stray capacitances, are subjected to rapidly switching currents, which can result in
unwanted voltage transients. To minimize inductance and ground loops, the length of the leads indicated by
heavy lines should be minimized. Optimal results can be achieved by single-point grounding (see
Figure 2)
or by
ground-plane construction. For the same reasons, the two programming resistors used in the adjustable version
should be located as close as possible to the regulator to keep the sensitive feedback wiring short.
Fixed Output Voltage Versions
FEEDBACK
4
LM2575-xx
Fixed Output
OUTPUT
2
V
IN
Unregulated
DC Input
+
3
C
IN
100
µF
GND
5 ON/OFF
L1
330
µH
D1
+
C
OUT
330
µF
L
O
A
D
V
OUT
+V
IN
1
C
IN
= 100
µF,
Aluminum Electrolytic
C
OUT
= 330
µF,
Aluminum Electrolytic
D1 = Schottky
L1 = 330
µH
Adjustable Output Voltage Versions
FEEDBACK
4
LM2575
(ADJ)
OUTPUT
2
7-V to 60-V
Unregulated
DC Input
+
C
IN
100
µF
3 GND
5
ON/OFF
L1
330
µH
R2
D1
11DQ06
+
C
OUT
330
µF
R1
L
O
A
D
V
OUT
+V
IN
1
V
OUT
= V
REF
(1 + R2/R1) = 5 V
Where,
V
REF
= 1.23 V
R1 = 2 kW
R2 = 6.12 kW
A.
Pin numbers are for the KTT (TO-263) package.
Figure 2. Test Circuit and Layout Guidelines
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