TL H 12593
LM2598
SIMPLE
SWITCHER
Power
Converter
150
kHz
1A
Step-Down
Voltage
Regulator
with
Features
May 1996
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 fre-
quency compensation
improved line and load specifica-
tions 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 regu-
lators 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 50 C 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
g
4% tolerance on out-
put voltage under all conditions of input voltage and output
load conditions and
g
15% on the oscillator frequency Ex-
ternal shutdown is included featuring typically 85 mA stand-
by current Self protection features include a two stage cur-
rent limit for the output switch and an over temperature
shutdown for complete protection under fault conditions
Features
Y
3 3V 5V 12V and adjustable output versions
Y
Adjustable version output voltage range 1 2V to 37V
g
4% max over line and load conditions
Y
Guaranteed 1A output current
Y
Available in 7-pin TO-220 and TO-263 (surface mount)
package
Y
Input voltage range up to 40V
Y
Excellent line and load regulation specifications
Y
150 kHz fixed frequency internal oscillator
Y
Shutdown Soft-start
Y
Out of regulation error flag
Y
Error output delay
Y
Low power standby mode I
Q
typically 85 mA
Y
High Efficiency
Y
Uses readily available standard inductors
Y
Thermal shutdown and current limit protection
Applications
Y
Simple high-efficiency step-down (buck) regulator
Y
Efficient pre-regulator for linear regulators
Y
On-card switching regulators
Y
Positive to Negative converter
Typical Application
(Fixed Output Voltage Versions)
TL H 12593 1
Patent Number 5 382 918
SIMPLE SWITCHER
and
Switchers Made Simple
are registered trademarks of National Semiconductor Corporation
C1996 National Semiconductor Corporation
RRD-B30M66 Printed in U S A
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
b
0 3
s
V
s
45V
Feedback Pin Voltage
b
0 3
s
V
s
a
25V
Output Voltage to Ground (Steady State)
b
1V
Power Dissipation
Internally limited
Storage Temperature Range
b
65 C to
a
150 C
ESD Susceptibility
Human Body Model (Note 3)
2 kV
Lead Temperature
S Package
Vapor Phase (60 sec )
a
215 C
Infrared (10 sec )
a
245 C
T Package (Soldering 10 sec )
a
260 C
Maximum Junction Temperature
a
150 C
Operating Conditions
Temperature Range
b
25 C
s
T
J
a
125 C
Supply Voltage
4 5V to 40V
LM2598-3 3
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range
Symbol
Parameter
Conditions
LM2598-3 3
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS
(Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
4 75V
s
V
IN
s
40V 0 1A
s
I
LOAD
s
1A
3 3
V
3 168 3 135
V(min)
3 432 3 465
V(max)
h
Efficiency
V
IN
e
12V I
LOAD
e
1A
78
%
LM2598-5 0
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range
Symbol
Parameter
Conditions
LM2598-5 0
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS
(Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
7V
s
V
IN
s
40V 0 1A
s
I
LOAD
s
1A
5
V
4 800 4 750
V(min)
5 200 5 250
V(max)
h
Efficiency
V
IN
e
12V I
LOAD
e
1A
82
%
LM2598-12
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range
Symbol
Parameter
Conditions
LM2598-12
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS
(Note 6) Test Circuit
Figure 1
V
OUT
Output Voltage
15V
s
V
IN
s
40V 0 1A
s
I
LOAD
s
1A
12
V
11 52 11 40
V(min)
12 48 12 60
V(max)
h
Efficiency
V
IN
e
25V I
LOAD
e
1A
90
%
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LM2598-ADJ
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range
Symbol
Parameter
Conditions
LM2598-ADJ
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
SYSTEM PARAMETERS
(Note 6) Test Circuit
Figure 1
V
FB
Feedback Voltage
4 5V
s
V
IN
s
40V 0 1A
s
I
LOAD
s
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)
h
Efficiency
V
IN
e
12V V
OUT
e
3V I
LOAD
e
1A
78
%
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range Unless otherwise specified V
IN
e
12V for the 3 3V 5V and
Adjustable version and V
IN
e
24V for the 12V version I
LOAD
e
200 mA
Symbol
Parameter
Conditions
LM2598-XX
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
DEVICE PARAMETERS
I
b
Feedback Bias Current
Adjustable Version Only V
FB
e
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
e
1A (Notes 8 and 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 (Notes 8 and 9)
1 5
A
1 2 1 15
A(min)
2 4 2 6
A(max)
I
L
Output Leakage Current
(Notes 8 10 and 11)
Output
e
0V
50
m
A(max)
Output
e b
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
e
0V (Note 11)
85
m
A
Current
200 250
m
A(max)
i
JC
Thermal Resistance
TO220 or TO263 Package Junction to Case
2
C W
i
JA
TO220 Package Junction to Ambient (Note 12)
50
C W
i
JA
TO263 Package Junction to Ambient (Note 13)
50
C W
i
JA
TO263 Package Junction to Ambient (Note 14)
30
C W
i
JA
TO263 Package Junction to Ambient (Note 15)
20
C W
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All Output Voltage Versions
(Continued)
Electrical Characteristics
Specifications with standard type face are for T
J
e
25 C and those with boldface
type apply over full Operating Temperature Range Unless otherwise specified V
IN
e
12V for the 3 3V 5V and
Adjustable version and V
IN
e
24V for the 12V version I
LOAD
e
200 mA
Symbol
Parameter
Conditions
LM2598-XX
(Limits)
Units
Typ
Limit
(Note 4)
(Note 5)
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
e
20% of Nominal Output Voltage
2
V
V
OUT
e
100% of Nominal Output Voltage
3
I
SD
Shutdown Current
V
SHUTDOWN
e
0 5V
5
m
A
10
m
A(max)
I
SS
Soft-start Current
V
Soft-start
e
2 5V
1 6
m
A
5
m
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
e
3 mA
0 3
V
Voltage
V
DELAY
e
0 5V
0 7 1 0
V(max)
IF
L
Flag Output Leakage Current
V
FLAG
e
40V
0 3
m
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
e
0 5V
3
m
A
6
m
A(max)
Delay Pin Saturation
Low (Flag ON)
55
mV
350 400
mV(max)
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Electrical Characteristics
(Continued)
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 25 C 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
e
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
Typical Performance Characteristics
(Circuit of
Figure 1 )
Normalized
Output Voltage
TL H 12593 2
Line Regulation
TL H 12593 3
Efficiency
TL H 12593 14
Switch Saturation
Voltage
TL H 12593 15
Switch Current Limit
TL H 12593 16
Dropout Voltage
TL H 12593 17
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