LM2594
0.5 A, Step-Down Switching
Regulator
The LM2594 regulator is monolithic integrated circuit ideally suited
for easy and convenient design of a step−down switching regulator
(buck converter). It is capable of driving a 0.5 A load with excellent
line and load regulation. This device is available in adjustable output
version. It is internally compensated to minimize the number of
external components to simplify the power supply design.
Since LM2594 converter is a switch−mode power supply, its
efficiency is significantly higher in comparison with popular
three−terminal linear regulators, especially with higher input voltages.
The LM2594 operates at a switching frequency of 150 kHz thus
allowing smaller sized filter components than what would be needed
with lower frequency switching regulators. Available in a standard
8−Lead PDIP and 8−Lead Surface Mount packages.
The other features include a guaranteed
$4%
tolerance on output
voltage within specified input voltages and output load conditions, and
$15%
on the oscillator frequency. External shutdown is included,
featuring 50
mA
(typical) standby current. Self protection features
include switch cycle−by−cycle current limit for the output switch, as
well as thermal shutdown for complete protection under fault
conditions.
Features
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MARKING
DIAGRAMS
8
1
SOIC−8
D SUFFIX
CASE 751
8
LM2594
AYWW
G
1
2594−ADJ
AWL
YYWW
PDIP−8
N SUFFIX
CASE 626
A
WL
YY
WW
G or
G
= Assembly Location
= Wafer Lot
= Year
= Work Week
= Pb−Free Package
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Adjustable Output Voltage Range 1.23 V
−
37 V
Guaranteed 0.5 A Output Load Current
Wide Input Voltage Range up to 40 V
150 kHz Fixed Frequency Internal Oscillator
TTL Shutdown Capability
Low Power Standby Mode, typ 50
mA
Thermal Shutdown and Current Limit Protection
Internal Loop Compensation
Moisture Sensitivity Level (MSL) Equals 1
These are Pb−Free Devices
Simple High−Efficiency Step−Down (Buck) Regulator
Efficient Pre−Regulator for Linear Regulators
On−Card Switching Regulators
Positive to Negative Converter (Buck−Boost)
Negative Step−Up Converters
Power Supply for Battery Chargers
PIN CONNECTIONS
SOIC−8
NC
NC
NC
FB
1
2
3
4
8 OUTPUT
7 V
IN
6 GND
5 ON/OFF
Applications
NC
NC
NC
FB
(Top View)
PDIP−8
1
2
3
4
8
7
6
5
OUTPUT
V
IN
GND
ON/OFF
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 23 of this data sheet.
©
Semiconductor Components Industries, LLC, 2009
January, 2009
−
Rev. 0
1
Publication Order Number:
LM2594/D
LM2594
12 V
Unregulated
DC Input
+V
IN
LM2594
7
Output
8
C
IN
= 68
mF
5
ON/OFF
6
GND
C
OUT
D1
1N5817
220
mF
Feedback
4
L1
100
mH
C
FF
R1 = 1 kW
R2 = 3k
V
OUT
= 5 V; I
load
= 0.5 A
Figure 1. Typical Application
0.5
Figure 2. Representative Block Diagram
PIN FUNCTION DESCRIPTION
Pin No.
1
−
3
4
5
Symbol
NC
FB
ON/OFF
Not Connected
This pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to
allow programming of the output voltage.
Allows the switching regulator circuit to be shut down using logic levels, thus dropping the total input supply
current to approximately 50
mA.
The threshold voltage is typical. 1.6 V. Applying a voltage above this value
(up to V
IN
) shuts the regulator off. If the voltage applied to this pin is lower than 1.6 V or if this pin is left open,
the regulator will be in the “on” condition.
Circuit ground pin. See the information about the printed circuit board layout.
Positive input supply for LM2594 step−down switching regulator. In order to minimize voltage transients and
to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present
(C
IN
in Figure 1)
Emitter of the internal switch. The saturation voltage Vsat of the output switch is typically 1 V. It should be
kept in mind that PCB area connected to this pin should be kept to a minimum in order to minimize coupling
to sensitive circuitry
Description (Refer to Figure 1)
6
7
GND
+V
IN
8
OUTPUT
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LM2594
MAXIMUM RATINGS
Symbol
V
in
ON/OFF
V
out
P
D
R
qJA
R
qJC
P
D
R
qJA
T
stg
−
−
T
J
Maximum Supply Voltage
ON/OFF Pin Input Voltage
Output Voltage to Ground (Steady−State)
Power Dissipation
8−Lead DIP
Thermal Resistance, Junction−to−Ambient
Thermal Resistance, Junction−to−Case
Power Dissipation
8−Lead Surface Mount
Thermal Resistance, Junction−to−Ambient
Storage Temperature Range
Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 kW)
Lead Temperature (Soldering, 10 seconds)
Maximum Junction Temperature
Rating
Value
45
−0.3
V
≤
V
≤
+V
in
−1.0
Internally Limited
100
5.0
Internally Limited
175
−65
to +150
2.0
260
150
Unit
V
V
V
W
°C/W
°C/W
W
°C/W
°C
kV
°C
°C
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
OPERATING RATINGS
(Operating Ratings indicate conditions 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 table)
Symbol
T
J
V
IN
Operating Temperature Range
Supply Voltage
Rating
Value
−40
to +125
4.5 V to 40 V
Unit
°C
V
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LM2594
SYSTEM PARAMETERS
ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for T
J
= 25°C, and those with boldface type apply
over full Operating Temperature Range
−40°C
to +125°C
Characteristics
LM2594
(Note 1, Test Circuit Figure 16)
Feedback Voltage (V
in
= 12 V, I
Load
= 0.1 A, V
out
= 5.0 V, )
Feedback Voltage (8.0 V
≤
V
in
≤
40 V, 0.1 A
≤
I
Load
≤
0.5 A, V
out
= 5.0 V)
Efficiency (V
in
= 12 V, I
Load
= 0.5 A, V
out
= 5.0 V)
Characteristics
Feedback Bias Current (V
out
= 5.0 V)
Oscillator Frequency (Note 2)
Saturation Voltage (I
out
= 0.5 A, Notes 3 and 4)
Max Duty Cycle “ON” (Note 4)
Current Limit (Peak Current, Notes 3 and 4)
Output Leakage Current (Notes 5 and 6)
Output = 0 V
Output =
−1.0
V
Quiescent Current (Note 5)
Standby Quiescent Current (ON/OFF Pin = 5.0 V (“OFF”))
(Note 6)
ON/OFF PIN LOGIC INPUT
Threshold Voltage
V
out
= 0 V (Regulator OFF)
V
out
= Nominal Output Voltage (Regulator ON)
ON/OFF Pin Input Current
ON/OFF Pin = 5.0 V (Regulator OFF)
ON/OFF Pin = 0 V (regulator ON)
I
IH
I
IL
−
−
15
0.01
30
5.0
mA
mA
V
IH
V
IL
2.2
2.4
1.0
0.8
1.6
V
V
V
V
FB_nom
V
FB
η
Symbol
I
b
f
osc
V
sat
DC
I
CL
I
L
0.7
0.65
135
120
1.193
1.18
−
Min
80
Typ
25
150
1.0
95
1.0
1.6
1.8
2.0
30
10
200
250
Max
100
200
165
180
1.2
1.4
1.23
1.267
1.28
V
V
%
Unit
nA
kHz
V
%
A
mA
Symbol
Min
Typ
Max
Unit
0.5
13
5.0
50
I
Q
I
stby
mA
mA
1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance.
When the LM2594 is used as shown in the Figure 16 test circuit, system performance will be as shown in system parameters section.
2. The oscillator frequency reduces to approximately 30 kHz in the event of an output short or an overload which causes the regulated output
voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC by
lowering the minimum duty cycle from 5% down to approximately 2%.
3. No diode, inductor or capacitor connected to output (Pin 8) sourcing the current.
4. Feedback (Pin 4) removed from output and connected to 0 V.
5. Feedback (Pin 4) removed from output and connected to +12 V to force the output transistor “off”.
6. V
in
= 40 V.
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LM2594
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 16)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
−0.2
−0.4
−0.6
0
5.0
10
15
20
25
30
35
40
V
out
= 5 V
V
out
, OUTPUT VOLTAGE CHANGE (%)
1.0
Vout , OUTPUT VOLTAGE CHANGE (%)
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
−50
−25
0
25
50
75
100
125
V
in
= 20 V
I
Load
= 100 mA
Normalized at T
J
= 25°C
I
Load
= 100 mA
T
J
= 25°C
T
J
, JUNCTION TEMPERATURE (°C)
V
in
, INPUT VOLTAGE (V)
Figure 3. Normalized Output Voltage
Figure 4. Line Regulation
2.0
INPUT - OUTPUT DIFFERENTIAL (V)
I O, OUTPUT CURRENT (A)
1.3
1.2
1.1
1.0
0.9
0.8
0.7
125
0.6
−50
−25
0
25
60
75
V
in
= 12 V
1.5
I
Load
= 500 mA
1.0
I
Load
= 100 mA
0.5
L = 100
mH
R_ind = 30 mW
0
−50
−25
0
25
60
75
100
100
125
T
J
, JUNCTION TEMPERATURE (°C)
T
J
, JUNCTION TEMPERATURE (°C)
Figure 5. Dropout Voltage
12
I Q, QUIESCENT CURRENT (mA)
11
10
9
8
7
6
5
4
0
5
10
15
20
25
30
35
40
I
Load
= 100 mA
160
I stby , STANDBY QUIESCENT CURRENT (
μA)
140
120
100
80
60
40
20
0
−50
−25
Figure 6. Current Limit
V
out
= 5 V
Measured at GND Pin
T
J
= 25°C
I
Load
= 500 mA
V
ON/OFF
= 5.0 V
V
in
= 40 V
V
in
= 12 V
0
25
60
75
100
125
V
in
, INPUT VOLTAGE (V)
T
J
, JUNCTION TEMPERATURE (°C)
Figure 7. Quiescent Current
Figure 8. Standby Quiescent Current
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