LM2598
SIMPLE SWITCHER
Power Converter 150 kHz
1A Step-Down Voltage Regulator, with Features
General Description
The LM2598 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 1A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5V, 12V, and an adjust-
able output version.
This series of switching regulators is similar to the LM2595
series, with additional supervisory and performance features
added.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation
, improved line and load specifications,
fixed-frequency oscillator, Shutdown /Soft-start, error flag
delay and error flag output.
The LM2598 series 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 7-lead TO-220 package with several
different lead bend options, and a 7-lead TO-263 surface
mount package. Typically, for output voltages less than 12V,
and ambient temperatures less than 50C, no heat sink is
required.
A standard series of inductors (both through hole and sur-
face mount types) are available from several different manu-
facturers optimized for use with the LM2598 series. This
feature greatly simplifies the design of switch-mode power
supplies.
Other features include a guaranteed
4% tolerance on out-
put voltage under all conditions of input voltage and output
load conditions, and
15% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 85 A
standby current. Self protection features include a two stage
current limit for the output switch and an over temperature
shutdown for complete protection under fault conditions.
Features
n
3.3V, 5V, 12V, and adjustable output versions
n
Adjustable version output voltage range, 1.2V to 37V
4% max over line and load conditions
n
Guaranteed 1A output current
n
Available in 7-pin TO-220 and TO-263 (surface mount)
package
n
Input voltage range up to 40V
n
Excellent line and load regulation specifications
n
150 kHz fixed frequency internal oscillator
n
Shutdown /Soft-start
n
Out of regulation error flag
n
Error output delay
n
Low power standby mode, I
Q
typically 85 A
n
High Efficiency
n
Uses readily available standard inductors
n
Thermal shutdown and current limit protection
Applications
n
Simple high-efficiency step-down (buck) regulator
n
Efficient pre-regulator for linear regulators
n
On-card switching regulators
n
Positive to Negative converter
Typical Application
(Fixed Output Voltage Versions)
Patent Number 5,382,918.
SIMPLE SWITCHER
and
Switchers Made Simple
are registered trademarks of National Semiconductor Corporation.
DS012593-1
January 2001
LM2598
SIMPLE
SWITCHER
Power
Converter
150
kHz
1A
Step-Down
V
oltage
Regulator
,
with
Features
2001 National Semiconductor Corporation
DS012593
www.national.com
Connection Diagrams and Order Information
Bent and Staggered Leads, Through Hole Package
7-Lead TO-220 (T)
DS012593-50
Order Number LM2598T-3.3, LM2598T-5.0,
LM2598T-12 or LM2598T-ADJ
See NS Package Number TA07B
Surface Mount Package
7-Lead TO-263 (S)
DS012593-22
Order Number LM2598S-3.3, LM2598S-5.0,
LM2598S-12 or LM2598S-ADJ
See NS Package Number TS7B
LM2598
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Supply Voltage (V
IN
)
45V
SD/SS Pin Input Voltage (Note 2)
6V
Delay Pin Voltage (Note 2)
1.5V
Flag Pin Voltage
-0.3
V
+45V
Feedback Pin Voltage
-0.3
V
+25V
Output Voltage to Ground
(Steady State)
-1V
Power Dissipation
Internally limited
Storage Temperature Range
-65C to +150C
ESD Susceptibility
Human Body Model (Note 3)
2 kV
Lead Temperature
S Package
Vapor Phase (60 sec.)
+215C
Infrared (10 sec.)
+245C
T Package (Soldering, 10 sec.)
+260C
Maximum Junction Temperature
+150C
Operating Conditions
Temperature Range
-25C
T
J
+125C
Supply Voltage
4.5V to 40V
LM2598-3.3
Electrical Characteristics
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
LM2598-3.3
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
4.75V
V
IN
40V, 0.1A
I
LOAD
1A
3.3
V
3.168/3.135
V(min)
3.432/3.465
V(max)
Efficiency
V
IN
= 12V, I
LOAD
= 1A
78
%
LM2598-5.0
Electrical Characteristics
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
LM2598-5.0
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
7V
V
IN
40V, 0.1A
I
LOAD
1A
5
V
4.800/4.750
V(min)
5.200/5.250
V(max)
Efficiency
V
IN
= 12V, I
LOAD
= 1A
82
%
LM2598-12
Electrical Characteristics
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
LM2598-12
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
15V
V
IN
40V, 0.1A
I
LOAD
1A
12
V
11.52/11.40
V(min)
12.48/12.60
V(max)
Efficiency
V
IN
= 25V, I
LOAD
= 1A
90
%
LM2598
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3
LM2598-ADJ
Electrical Characteristics
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range.
Symbol
Parameter
Conditions
LM2598-ADJ
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit
Figure 1
V
FB
Feedback Voltage
4.5V
V
IN
40V, 0.1A
I
LOAD
1A
1.230
V
V
OUT
programmed for 3V. Circuit of
Figure 12.
1.193/1.180
V(min)
1.267/1.280
V(max)
Efficiency
V
IN
= 12V, V
OUT
= 3V, I
LOAD
= 1A
78
%
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable version and V
IN
= 24V for the 12V ver-
sion. I
LOAD
= 200 mA
Symbol
Parameter
Conditions
LM2598-XX
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
DEVICE PARAMETERS
I
b
Feedback Bias Current
Adjustable Version Only, V
FB
= 1.3V
10
nA
50/100
nA(max)
f
O
Oscillator Frequency
(Note 7)
150
kHz
127/110
kHz(min)
173/173
kHz(max)
V
SAT
Saturation Voltage
I
OUT
= 1A (Note 8) (Note 9)
1
V
1.2/1.3
V(max)
DC
Max Duty Cycle (ON)
(Note 9)
100
%
Min Duty Cycle (OFF)
(Note 10)
0
I
CL
Current Limit
Peak Current, (Note 8) (Note 9)
1.5
A
1.2/1.15
A(min)
2.4/2.6
A(max)
I
L
Output Leakage Current
Output = 0V (Note 9) (Note 10) (Note 11)
50
A(max)
Output = -1V
2
mA
15
mA(max)
I
Q
Operating Quiescent
SD /SS Pin Open, (Note 10)
5
mA
Current
10
mA(max)
I
STBY
Standby Quiescent
SD /SS pin = 0V, (Note 11)
85
A
Current
200/250
A(max)
JC
Thermal Resistance
TO220 or TO263 Package, Junction to Case
2
C/W
JA
TO220 Package, Junction to Ambient (Note 12)
50
C/W
JA
TO263 Package, Junction to Ambient (Note 13)
50
C/W
JA
TO263 Package, Junction to Ambient (Note 14)
30
C/W
JA
TO263 Package, Junction to Ambient (Note 15)
20
C/W
SHUTDOWN/SOFT-START CONTROL Test Circuit of
Figure 1
V
SD
Shutdown Threshold
1.3
V
Voltage
Low, (Shutdown Mode)
0.6
V(max)
High, (Soft-start Mode)
2
V(min)
V
SS
Soft-start Voltage
V
OUT
= 20% of Nominal Output Voltage
2
V
V
OUT
= 100% of Nominal Output Voltage
3
LM2598
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4
All Output Voltage Versions
Electrical Characteristics
(Continued)
Specifications with standard type face are for T
J
= 25C, and those with boldface type apply over full Operating Tempera-
ture Range. Unless otherwise specified, V
IN
= 12V for the 3.3V, 5V, and Adjustable version and V
IN
= 24V for the 12V ver-
sion. I
LOAD
= 200 mA
Symbol
Parameter
Conditions
LM2598-XX
Units
(Limits)
Typ
Limit
(Note 4)
(Note 5)
SHUTDOWN/SOFT-START CONTROL Test Circuit of
Figure 1
I
SD
Shutdown Current
V
SHUTDOWN
= 0.5V
5
A
10
A(max)
I
SS
Soft-start Current
V
Soft-start
= 2.5V
1.6
A
5
A(max)
FLAG/DELAY CONTROL Test Circuit of
Figure 1
Regulator Dropout Detector
Low (Flag ON)
96
%
Threshold Voltage
92
%(min)
98
%(max)
VF
SAT
Flag Output Saturation
I
SINK
= 3 mA
0.3
V
Voltage
V
DELAY
= 0.5V
0.7/1.0
V(max)
IF
L
Flag Output Leakage
Current
V
FLAG
= 40V
0.3
A
Delay Pin Threshold
1.25
V
Voltage
Low (Flag ON)
1.21
V(min)
High (Flag OFF) and V
OUT
Regulated
1.29
V(max)
Delay Pin Source Current
V
DELAY
= 0.5V
3
A
6
A(max)
Delay Pin Saturation
Low (Flag ON)
55
mV
350/400
mV(max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. 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.
Note 2: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 1 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 4: Typical numbers are at 25C and represent the most likely norm.
Note 5: 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 correlation using standard Statistical Quality Control (SQC) methods. All limits are used
to calculate Average Outgoing Quality Level (AOQL).
Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2598
is used as shown in the
Figure 1
test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 7: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current
overload.
Note 8: No diode, inductor or capacitor connected to output pin.
Note 9: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 10: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor
switch OFF.
Note 11: V
IN
= 40V.
Note 12: Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board
with (1 oz.) copper area of approximately 1 in
2
.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 0.5 in
2
of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in
2
of (1 oz.) copper area.
Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in
2
of (1 oz.) copper area on
the LM2598S side of the board, and approximately 16 in
2
of copper on the other side of the p-c board. See application hints in this data sheet and the thermal model
in
Switchers Made Simple
version 4.2 software.
LM2598
www.national.com
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