LM2596 [ESTEK]
Simple high-efficiency step-down (buck) regulator; 简单的高英法fi效率步降（降压）稳压器
| 型号： | LM2596 |
| 厂家： | 
Estek Electronics Co. Ltd |
| 描述： | Simple high-efficiency step-down (buck) regulator |
| 文件： | 总13页 (文件大小：388K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM2596
GENERAL DESCRIPTION
FEATURES
The LM2596 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 3A load with
excellent line and load regulation. These devices are available
in fixed output voltages of 3.3V, 5V, 12V, and an adjustable
output version.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation, and a fixed-frequency oscillator.
The LM2596 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 5-lead TO-220 package with several
different lead bend options, and a 5-lead TO-263 surface mount
package.
3.3V, 5V, 12V, and adjustable output versions
Adjustable version output voltage range, 1.2V to 37V
4% max over line and load conditions
Available in TO-220 and TO-263 packages
Guaranteed 3A output load current
Input voltage range up to 40V
Requires only 4 external components
Excellent line and load regulation specifications
150 kHz fixed frequency internal oscillator
TTL shutdown capability
Low power standby mode, IQ typically 80 µA
High efficiency
Uses readily available standard inductors
Thermal shutdown and current limit protection
A standard series of inductors are available from several
different manufacturers optimized for use with the LM2596
series. This feature greatly simplifies the design of switch-mode
power supplies.
APPLICATIONS
Simplehigh-efficiencystep-down (buck) regulator
On-card switching regulators
Positive to negative converter
Other features include a guaranteed 4% tolerance on output
voltage under specified input voltage and output load
conditions, and 15% on the oscillator frequency. External
shutdown is included, featuring typically 80 µA standby
current. Self protection features include a two stage frequency
reducing current limit for the output switch and an over
temperature shutdown for complete protection under fault
conditions.
TYPICAL APPLICATION (Fixed Output Voltage Versions)
4
+V
IN
12V
L1
5.0V
1
5.0
+
CIN
680
2
+
COUT
220
5
3
F
BLOCK DIAGRAM
ON/OFF
V
IN
+
+
START
UP
+
COM
-
2.5V
-
COM
+
FEEDBACK
GM
AMP
+
R2
-
-
LATCH
DRIVER
Active
capacitor
+
+
-
OUTPUT
GND
150kHz
OSC
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LM2596
PIN FUNCTIONS
ABSOLUTE MAXIMUM RATINGS (Note 1)
Maximum Supply Voltage
ON /OFF Pin Input Voltage
+25V
45V
+VIN - This is the positive input supply for the IC switching
regulator. A suitable input bypass capacitor must be present at
this pin to minimize voltage transients and to supply the
switching currents needed by the regulator.
-0.3
V
Feedback Pin Voltage
Output Voltage to Ground
(Steady State)
-0.3 V +25V
Ground - Circuit ground.
Output - Internal switch. The voltage at this pin switches
between (+VIN - VSAT ) and approximately -0.5V, with a duty
cycle of approximately VOUT /VIN. To minimize coupling to
sensitive circuitry, the PC board copper area connected to this
pin should be kept to a minimum.
-1V
Power Dissipation
Internally limited
0C to +1500SCtorage Temperature Range
ESD Susceptibility
-65
Human Body Model (Note 2)
Lead Temperature
2 kV
Feedback — Senses the regulated output voltage to complete
the feedback loop.
S Package
Vapor Phase (60 sec.)
Infrared (10 sec.)
T Package (Soldering, 10 sec.)
Maximum Junction Temperature
+2150C
ON/OFF - Allows the switching regulator circuit to be shut
down using logic level signals thus dropping the total input
supply current to approximately 80 µA. Pulling this pin below a
threshold voltage of approximately 1.3V turns the regulator on,
and pulling this pin above 1.3V (up to a maximum of 25V) shuts
the regulator down. If this shutdown feature is not needed, the
ON /OFF pin can be wired to the ground pin or it can be left
+2450C
+2600C
+1500C
OPERATING CONDITIONS
Temperature Range
-400C +1250C
TJ
LM2596-3.3
ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature
Range
LM2596-3.3
Units
(Limits)
Symbol
Parameter
Conditions
Typ
Limit
(Note 3)
(Note 4)
SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1
V
VOUT
Output Voltage
4.7V5
VIN40V, 0.2AILOAD3A
3.3
3.168/3.135
3.432/3.465
V(min)
V(max)
73
Efficiency
%
VIN=12V, ILOAD=3A
LM2596-5.0
ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature
LM2596-5.0
Units
(Limits)
Symbol
Parameter
Conditions
Typ
Limit
(Note 3)
(Note 4)
SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1
V
VOUT
Output Voltage
7V
VIN40V, 0.2AILOAD3A
5.0
4.800/4.750
5.200/5.250
V(min)
V(max)
80
Efficiency
%
VIN=12V, ILOAD=3A
LM2596-12
ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature
LM2596-12
Units
(Limits)
Symbol
Parameter
Conditions
Typ
Limit
(Note 3)
(Note 4)
SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1
V
VOUT
Output Voltage
15V
VIN40V, 0.2AILOAD3A
12.0
11.52/11.40
12.48/12.60
V(min)
V(max)
90
Efficiency
%
VIN=12V, ILOAD=3A
LM2596-ADJ
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LM2596
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating
Temperature Range
LM2596-ADJ
Units
(Limits)
Symbol
Parameter
Conditions
Typ
Limit
(Note 3)
(Note 4)
SYSTEM PARAMETERS (Note 5)Test Circuit Figure 1
1.230
V
VOUT
Output Voltage
4.5VVIN40V, 0.2AILOAD3A
VOUT programmed for 3V. Circuit of
Figure 1.
1.193/1.180
1.267/1.280
V(min)
V(max)
Efficiency
VIN=12V, VOUT=3V, ILOAD=3A
ALL OUTPUT VOLTAGE VERSIONS
ELECTRICAL CHARACTERISTICS
Specifications with standard type face are for TJ = 250C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD
= 500 mA
LM2596-XX
Units
(Limits)
Symbol
Parameter
Conditions
Typ
(Note 3)
Limit
(Note 4)
DEVICE PARAMETERS
nA
nA (max)
kHz
Feedback Bias Current
Adjustable Version Only, VFB=1.3V
(Note 6)
10
I
b
50/100
fO
Oscillator Frequency
150
kHz (min)
kHz (max)
V
127/110
173/173
VSAT
DC
ICL
Saturation Voltage
IOUT=3A (Notes 7, 8)
1.16
V (max)
1.4/1.5
(Note 8)
(Note 9)
Peak Current (Notes 7, 8)
100
0
4.5
Max Duty Cycle (ON)
Min Duty Cycle (OFF)
Current Limit
A
A (min)
A (max)
3.6/3.4
6.9/7.5
50
IL
Output Leakage Current
Output=0V (Notes 7, 9)
Output=-0.9V (Note 10)
A (max)
mA
10
5
30
10
mA (max)
mA
mA (max)
IQ
Quiescent Current
Standby
(Note 9)
ON/OFF pin=5V (OFF) (Note 10)
80
ISTBY
Quiescent
A
200/250
A (max)
0C/W
0C/W
0C/W
0C/W
0C/W
JC
JA
JA
JA
JA
Thermal Resistance
TO-220 orTO-263Package, Junction to Case
TO-220Package,Junction to Ambient(Note11)
TO-263Package,Junction to Ambient(Note12)
TO-263Package,Junction to Ambient(Note13)
TO-263Package,Junction to Ambient(Note14)
2
50
50
30
20
ON/OFF CONTROL Test Circuit Figure 1
ON/OFF Pin Logic Input
1.3
V
Threshold Voltage
Low (Regulator ON)
High (Regulator OFF)
V (max)
V (min)
VIH
VIL
0.6
2.0
IH
LOGIC=2.5V (Regulator OFF)
5
A
15
VON/OFF Pin Input Current
A (max)
VLOGIC=0.5V (Regulator ON)
0.02
A
5
A (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: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 3: Typical numbers are at 250C and represent the most likely norm.
Note 4: 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 5: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can
affect switching regulator system performance. When the LM2596 is used as shown in the Figure 1 test circuit, system performance
will be as shown in system parameters section of Electrical Characteristics.
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LM2596
Note 6: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is
determined by the severity of current over-load.
Note 7: No diode, inductor or capacitor connected to output pin.
Note 8: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 9: 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 10: VIN = 40V.
Note 11: 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 in2
Note 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in2
of (1 oz.) copper area.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with
2.5 in2 of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with
3 in2 of (1 oz.) copper area on the LM2596S side of the board, and approximately 16 in2 of copper on the other side of the p-c
board.
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1)
Normalized Output Voltage
1.5
Line Regulation
Efficiency
0.4
0.3
0.2
0.1
0
95
90
85
80
20V
1.0
0.5
0
12V
5V
5
-0.1
-0.2
-0.3
-0.5
-1.0
75
65
-0.4
-50 -25
0
25
50 75
0
5
10 15 20 25 30
0
10 15 20 25 30
35 40
35 40
Switch Saturation
Switch Current Limit
V =12VIN
Dropout Voltage
1.4
5.5
5.0
1.6
1.4
V =12V
IN
1.3
1.2
1.1
VOUT =5V
-0 40 C
T =
I
3A
50
1.2
4.5
4.0
3.5
1.0
0.9
0.8
0.7
0.6
=
LOAD
1.0
I
250C
10 25 C
1
0.6
-50 -25
0
25
50
-50 -25
0
25
0
2 3
4
SWITCH CURRENT (A)
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1) (Continued)
Operating
Quiescent Current
Shutdown
Quiescent Current
Minimum Operating
Supply Voltage
120
100
5
4
24
20
_
V
5V
I
0
20 5 C
T =
16
12
80
60
3
2
1
0
8
4
0
40
20
0
0
10
20
30
40
-50 -25
0
25
50
-50 -25
0
25
50
SUPPLY VOLTAGE (V)
ON/OFF Threshold
Voltage
ON/OFF Pin
Switching Frequency
Current (Sinking)
2.5
2.0
8
7
6
5
4
160
155
150
OFF
ON
1.5
1.0
0.5
145
140
3
2
135
130
1
0
-50 -25
0
25
50
-50 -25
0
25
50
10
15
20
25
0
ON/OF PIN VOLTAGE (V)
Feedback Pin
10
7.5
5.0
2.5
0
ADJUSTABLE VERSION ONLY
-2.5
-5.0
-50 -25
0
25
50
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LM2596
TYPICAL PERFORMANCE CHARACTERISTICS
Continuous Mode Switching Waveforms
VIN=20V, VOUT=5V, ILOAD=2A
Discontinuous Mode Switching Waveforms
VIN=20V, VOUT=5V, ILOAD=500mA L=10 H,
L=32H, COUT=220F, COUTESR=50m
COUT=330F, COUTESR=45m
20V
20V
10V
10V
A
A
0V
1A
0V
2A
B
C
B
C
1A
0A
0A
AC/
div
AC/
div
A: Output Pin Voltage,10V/ div
B: Inductor Current 1A/ div
A: Output Pin Voltage,10V/ div
B: Inductor Current 1A/ div
C: Output Ripple Voltage,50mV/ div
C: Output Ripple Voltage,100mV/div
Horizontal Time Base: 2s/ div
Horizontal Time Base: 2s/ div
Load Transient Response for Discontinuous Mode
VIN=20V, VOUT=5V, ILOAD=500mA to 2A
Load Transient Response for Continuous Mode
VIN=20V, VOUT=5V, ILOAD=500mA to 2A
L=10H, COUT=330F, COUTESR=45m
L=32H, COUT=220F, COUTESR=50m
A
AC
div
A
AC
div
B
1A
0A
B
1A
0A
A: Output Voltage,100mV/ div. (AC)
B: 500mA to 2A Load Pulse
A: Output Voltage,100mV/ div.(AC)
B: 500mA to 2A Load Pulse
/ div
Horizontal Time Base: 200s/div
Horizontal Time Base: 100
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LM2596
TEST CIRCUIT AND LAYOUT GUIDELINES
Fixed Output Voltage Versions
4
+V
IN
+
L1
+
L1
2
+
+
3
5
COUT
CIN
CIN
-
470
F
,50V,Aluminum Electrolytic Nichicon “PL
,25V,Aluminum Electrolytic Nichicon “PL
COUT - 220
Series” D1 - 5A,40V SchottkyRectifer,1N5825
,L38
L1
-
Adjustable Output Voltage Versions
CFF
R1
R2
4
+V
IN
+
L1
2
+
+
3
5
COUT
CIN
R
REF
2
V
(
V
1+
)
R1
where VREF=1.23V
V
OUT -1)
R =R (
2
Select R1 to be approximately1k
, use a1% resistor for best
CIN
-
470
,50V,Aluminum Electrolytic Nichicon “PL
COUT - 220
F
,35V,Aluminum Electrolytic Nichicon “PL
Series” D1 - 5A,40V SchottkyRectifer,1N5825
,L38
L1
R1
C
-
-
s
ee Application Information Section
Figure 1. Standard Test Circuits and Layout Guides
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance can generate
voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines should
be wide printed circuit traces and
should be kept as short as possible. For best results, external components should be located as close to the switcher lC as possible
using ground plane construction or single point grounding.
If open core inductors are used, special care must be taken as to the location and positioning of this type of inductor. Allowing
the inductor flux to intersect sensitive feedback, lC groundpath and COUT wiring can cause problems.
When using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated wiring.
Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor.
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LM2596
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT)
PROCEDURE (Fixed Output Voltage Version)
EXAMPLE (Fixed Output Voltage Version)
Given:
Given:
VOUT = Regulated Output Voltage (3.3V, 5V or 12V)
VIN (max) = Maximum DC Input Voltage
VOUT =5V
VIN (max) = 12V
1. Inductor Selection (L1)
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Figures
Figure 4, Figure 5,or Figure 6. (Output voltages of 3.3V, 5V, or
12V respectively.) For all other voltages, see the design procedure
for the adjustable version.
A. Use the inductor selection guide for the 5V version shown in Figure 5.
B. From the inductor value selection guide, identify the inductance B. From the inductor value selection guide shown in Figure 5, the
region intersected by the Maximum Input Voltage line and the
Maximum Load Current line. Each region is identified by an
inductance value and an inductor code (LXX).
inductance region intersected by the 12V horizontal line and the 3A
vertical line is 33 µH, and the inductor code is L40.
C. Select an appropriate inductor from the four manufacturer’s part C. The inductance value required is33 µH. Fromthetable in Figure8, go to the
numbers listed in Figure 8.
L40 line and choose an inductorpartnumber fromanyofthe four manufacturers
shown. (In most in-stance, both through hole and surface mount inductors are
available.)
2. Output Capacitor Selection (COUT
)
2. Output Capacitor Selection (COUT)
A. See section on output capacitors in application information section.
A. In the majority of applications, low ESR (Equivalent Series
Resistance) electrolytic capacitors between 82 µF and 820 µF and
low ESR solid tantalum capacitors between 10 µF and 470 µF
provide the best results. This capacitor should be located close to
the IC using short capacitor leads and short copper traces. Do not
use capacitors larger than 820 µF.
B. Fromthequickdesign component selection table shown in Figure2, locate the
5V output voltage section. In the load current column, choose theload current line
that is closest to the current needed in your application, for this example, use the3A
line. In themaximuminput voltage column, select thelinethat covers theinput
voltage needed in your application, in this example, use the15V line. Continuing on
this line are recommended inductors and capacitors that will providethebest overall
performance.
B. To simplify the capacitor selection procedure, refer to the quick
design component selection table shown in Figure 2. This table
contains different input voltages, output voltages, and load
currents, and lists various inductors and output capacitors that will
provide the best design solutions.
The capacitorlist contains both through hole electrolytic and surface mount tantalum
capacitors fromfourdifferent capacitor manufacturers. It is recommended that both
the manufacturers and the manufacturer’s series that are listed in the tablebe used.
In this example aluminumelectrolytic capacitors fromseveral different
manufacturers are available with the range ofESR numbers needed.
330 µF 35V PanasonicHFQSeries
330 µF 35V Nichicon PLSeries
C. The capacitor voltage rating for electrolytic capacitors should be C. Fora 5V output, a capacitor voltage rating at least 7.5V ormore is needed. But
even a lowESR, switchinggrade, 220µF 10V aluminumelectrolytic capacitor
would exhibit approximately225 mWofESR (see the curve in Figure 14 for the
ESR vs voltage rating). This amount ofESR would result in relativelyhigh output
ripple voltage. To reduce the rippleto 1%oftheoutput voltage, orless, a capacitor
with ahigher valueorwith ahigher voltage rating (lower ESR) should be selected.
at least 1.5 times greater than the output voltage, and often much
higher voltage ratings are needed to satisfy the low ESR
requirements for low output ripple voltage.
3. Catch Diode Selection (D1)
3. Catch Diode Selection (D1)
A. The catch diode current rating must beat least 1.3 times greater than the A. Refer to thetable shown in Figure 11. In this example, a5A, 20V, 1N5823
maximumload current. Also, ifthepower supplydesign must withstand a Schottkydiode willprovide thebestperformance, and willnot beoverstressed even
continuousoutput short, thediode should have a current ratingequal to the for a shorted output.
maximumcurrent limit ofthe LM2596. The most stressful condition for
thisdiode isan overload orshorted output condition.
B. The reverse voltage rating ofthediode should beat least 1.25 times the
maximuminput voltage.
C. This diode must be fast (short reverse recoverytime) and must be located
close to the LM2596 using short leads and short printed circuit traces.
Because oftheir fast switching speed and lowforward voltage drop,
Schottkydiodesprovidethebest performance and efficiency, and should be
the first choice, especiallyin lowoutput voltage applications.
Ultra-fast recovery, or High-Efficiencyrectifiers also provide good results.
Ultra-fast recoverydiodes typicallyhave reverse recoverytimes of50 nsor
less. Rectifiers such as the 1N5400 series are much too slowand should not
beused.
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LM2596
PROCEDURE (Fixed Output Voltage Version)
4. Input Capacitor (CIN)
A lowESRaluminumor tantalumbypass capacitor isneeded between the
inputpin and ground pin to prevent large volt-age transients from appearing
at the input. This capacitorshould belocated close to the IC
EXAMPLE (Fixed Output Voltage Version)
4. Input Capacitor (CIN)
The important parameters for the Input capacitor are the input voltage ratingand the
RMS current rating. With anominal
input voltage of12V, an aluminumelectrolytic capacitor with a voltage rating
using shortleads. In addition, the RMS current ratingofthe input capacitor greater than 18V (1.5 xVIN ) would be needed. The next higher capacitor voltage
rating is25V.
should be selected to be at least 1/2 the DC load current. The capacitor
manufacturers data sheet must be checked to assure that this current rating
is not exceeded. The curve shown in Figure 9 shows typical RMS current
ratings for several different aluminumelectrolytic capacitor values.
Foran aluminumelectrolytic, the capacitorvoltage rating should be
approximately1.5 times the maximuminput voltage.
The tantalumcapacitor voltage ratingshould be2 times the maximum
input voltage and it is recommended that theybe surge current tested by
the manufacturer.
The RMS current rating requirement for theinput capacitorin
a buck regulator is approximately1 /2 theDC load current. In this example, with a
3Aload, a capacitor with a RMS current rating ofat least 1.5Ais needed. The
curves shown in Figure9 can beused to select an appropriate input capacitor.
Fromthe curves, locate the35V line and note which capacitor values have RMS
current ratings greater than 1.5A. A680µF/35V capacitor could beused.
Fora through holedesign, a680µF/35V electrolytic capacitor (PanasonicHFQ
series or Nichicon PLseries or equivalent)would be adequate. other types or other
manufacturers capacitors can be used provided the RMS ripple current ratings are
adequate.
For surface mountdesigns, solid tantalumcapacitors can beused, but caution must
be exercised with regard to the capacitor surge current rating. The TPS series
available fromAVX, and the593D series fromSprague are both surge current
tested.
Use caution when using ceramic capacitors for input bypassing, because it
maycause severe ringing at theVpin.
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT) (Continued)
Output Capacitor
Conditions
Through Hole Electrolytic
Panasonic
Surface Mount Tantalum
AVXTPS
Series
Output
Voltage
(V)
Load
Current
(A)
Max Input
Voltage (V)
Inductance
H)
Inductor
(#)
Sprague 595DSeries
F/V)
Nichicon PL
HFQ Series
(
(
Series (F/V)
(F/V)
(F/V)
3.3
3
5
7
22
390/6.3
22
390/6.3
22
390/6.3
33
390/6.3
22
390/6.3
33
390/6.3
47
330/10
22
330/10
22
330/10
33
330/10
47
330/10
22
L41
L41
L41
L40
L33
L32
L39
L41
L41
L40
L39
L33
470/25
560/35
680/35
560/35
470/25
330/35
330/35
470/25
560/25
330/35
330/35
470/25
560/16
560/35
680/35
470/35
470/35
330/35
270/50
560/16
560/25
330/35
270/35
560/16
330/6.3
330/6.3
330/6.3
330/6.3
330/6.3
330/6.3
220/10
220/10
220/10
220/10
220/10
220/10
10
40
6
2
3
5
10
40
8
2
3
12
10
15
40
9
2
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (ADJUSTABLE OUTPUT)
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
Given:
Given:
VOUT = Regulated Output Voltage
VIN(max) = Maximum Input Voltage
ILOAD(max) = Maximum Load Current
VOUT = 20V
VIN(max) = 28V
ILOAD(max) = 3A
1. Programming Output Voltage (Selecting R1 and R2, as shown in
Figure 1)
1. Programming Output Voltage (Selecting R1 and R2, as shown
in Figure 1)
Use the following formula to select the appropriate resistor values.
Select R1 to be 1 k, 1%. Solve for R2.
R
R
2
V
OUT VREF (1
)
V
REF
1.23
V
OUT
20V
1
R
2
R
1
(
1)
1k(
1.23V
Select a value for R1 between 240
and 1.5k. The lower resistor
V
REF
values minimize noise pickup in the sensitive feedback pin. (For the
lowest temperature coefficient and the best stability with time, use 1%
metal film resistors.)
R2=1k (16.26-1)=15.26k, closest 1% value is 15.4k
R2 = 15.4 k
.
BEIJING ESTEK ELECTRONICS CO.,LTD
9
LM2596
PROCEDURE (Adjustable Output Voltage Version)
OUT
EXAMPLE (Adjustable Output Voltage Version)
V
R
2
R
1
(
1) VREF
2. Inductor Selection (L1)
2. Inductor Selection (L1)
the following formula:
(E T),
1000
D
200
V
1000
E T (V V V )
s)
IN
OUT
SAT
E
T
20
1.
kHz
1
0
150
VIN
VSATV
D
28
(V
s)
where VSAT = internal switch saturation voltage = 1.16V
and VD = diode forward voltage drop = 0.5V
E
T
(
.684
)
2. 05
B. Use the E
T value from the previous formula and match it with the
E
T number on the vertical axis of the Inductor Value Selection Guide
shown in Figure 7.
C. on the horizontal axis, select the maximum load current.
C.
D. From the inductor value selection guide shown in Figure 7, the
inductance region intersected by the 34 (V µs) horizontal line and
the 3A vertical line is 47 µH, and the inductor code is L39.
E. From the table in Figure 8, locate line L39, and select an
inductor part number from the list of manufacturers part numbers.
D. Identify the inductance region intersected by the ET value and the
Maximum Load Current value. Each region is identified by an
inductance value and an inductor code (LXX).
E. Select an appropriate inductor from the four manufacturer’s part
numbers listed in Figure 8.
3. Output Capacitor Selection (COUT
)
3. Output Capacitor SeIection (COUT)
A. In the majorityofapplications, lowESR electrolytic or solid tantalum
capacitors between 82 µF and 820 µF provide the best results. This capacitor
should be located close to the IC using short capacitor leads and short copper
traces. Do not use capacitors larger than 820 µF.
B. To simplify the capacitor selection procedure, refer to the quick
design table shown in Figure 3. This table contains different output
voltages, and lists various output capacitors that will provide the best
design solutions.
B. Fromthequickdesign table shown in Figure 3, locate theoutput voltage
column. Fromthat column, locate theoutput voltage closest to theoutput
voltage in yourapplication. In this example, select the24V line. Under the
output capacitor section, select a capacitor fromthe list ofthrough hole
electrolytic orsurface mount tantalumtypes fromfour different capacitor
manufacturers. It is recommended that both the manufacturers and the
manufacturers series that are listed in the tablebeused.
In this example, through hole aluminumelectrolytic capacitors from
several different manufacturers are available.
220 µF/35V Panasonic HFQ Series
150 µF/35V Nichicon PLSeries
C. The capacitor voltage rating should be at least 1.5 times greater than C. For a 20V output, a capacitor rating of at least 30V or more is
the output voltage, and often much higher voltage ratings are needed to needed. In this example, either a 35V or 50V capacitor would
satisfy the low ESR requirements needed for low output ripple voltage. work. A 35V rating was chosen, although a 50V rating could also
be used if a lower output ripple voltage is needed.
Other manufacturers or other types of capacitors may also be used,
provided the capacitor specifications (especially the 100 kHz
ESR) closely match the types listed in the table. Refer to the
capacitor manufacturers data sheet for this information.
4. Feedforward Capacitor (CFF ) (See Figure 1)
4. Feedforward Capacitor (CFF )
For output voltages greater than approximately 10V, an additional
capacitor is required. The compensation capacitor is typically between
100 pF and 33 nF, and is wired in parallel with the output voltage
setting resistor, R2. It provides additional stability for high output
voltages, low input-output voltages, and/or very low ESR output
capacitors, such as solid tantalum capacitors.
The table shown in Figure 3 contains feed forward capacitor
values for various output voltages. In this example, a 560 pF
capacitor is needed.
C
FF
1
3
31
10
This capacitor type can be ceramic, plastic, silver mica, etc. (Because of
the unstable characteristics of ceramic capacitors made with Z5U
material, they are not recommended.)
BEIJING ESTEK ELECTRONICS CO.,LTD
10
LM2596
LM2596 SERIES BUCK REGULATOR DESING PROCEDURE (ADJUSTABLE OUTPUT)
Through Hole Output Capacitor Surface Mount Output Capacitor
Output
Voltage (V)
Nichicon PL Series
AVX TPS Series
F/V)
Panasonic HFQ
Series
Sprague 595D
Series
Feedforward
Capacitor
Feedforward
(
(
F/V)
(
F/V)
(F/V)
2
4
6
820/35
560/35
470/25
330/25
330/25
220/35
220/35
100/50
820/35
470/35
470/25
330/25
330/25
220/35
150/35
100/50
33 nF
10 nF
3.3 nF
1.5 nF
1 nF
680 pF
560 pF
390 pF
330/6.3
330/6.3
220/10
100/16
100/16
68/20
470/4
390/6.3
330/10
180/16
180/16
120/20
33/25
33 nF
10 nF
3.3 nF
1.5 nF
1 nF
680 pF
220 pF
220 pF
9
12
15
24
28
33/25
10/35
15/50
Figure 3. Output Capacitor and Feedforward Capacitor Selection Table
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE
Inductor Value Selection Guides (For Continuous Mode Operation)
40V
30V
25V
40V
L29
20V
L43
L39
L30
L27
L36
L40
L31
L37
L38
L21
L22
L32
10V
L28
20V
19V
18V
17V
L33
L30
8V
7V
L29
L40
L31
L23
L34
L21
16V
L32
6V
L24
L25
L33
L22
L23
15V
14V
L15
L24
L34
L16
5V
0.6 0.8 1.0 1.5 2.0 2.5
3.0
0.6 0.8 1.0 1.5 2.0 2.5
3.0
Figure 6. LM2596-12
Figure 4. LM2596-3.3
BEIJING ESTEK ELECTRONICS CO.,LTD
11
LM2596
70
60
50
40V
20V
15V
Figure 7. LM2596-ADJ
L38
L29
L27
L35
L28
L39
L40
L43
L30
L36
L44
L37
40
L31
12V
L29
L38
L39
L40
30
25
L21
L22
L32
10V
9V
L30
20
15
L31
L32
L21
L22
L23
L33
L34
L33
L34
8V
10
9
L23
8
L24
L24
7
6
L15
5
4
L25
L25
7V
0.6 0.8 1.0
3.0
1.5 2.0 2.5
0.6 0.8 1.0
3.0
1.5 2.0 2.5
MAXIMUM LOAD CURRENT (A)
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (Continued)
Cur-
rent
(A)
Schott
Through
Hole
Renco
Through
Hole
Pulse
Surface Mount
Surface
Mount
Through Hole
RL-1284-22-43
RL-5471-5
RL-5471-6
RL-5471-7
RL-1283-22-43
RL-1283-15-43
RL-5471-1
RL-5471-2
RL-5471-3
RL-5471-4
RL-5471-5
RL-5471-6
RL-5471-7
RL-1283-22-43
Surface
Mount
RL1500-22
Surface
Mount
(H)
L15
DO3308-223
L21 68
DO3316-683
L22 47
DO3316-473
L23 33
DO3316-333
L24 22
DO3316-223
L25 15
DO3316-153
L26 330
DO5022P-334
L27 220
DO5022P-224
L28 150
DO5022P-154
L29 100
DO5022P-104
L30 68
DO5022P-683
L31 47
DO5022P-473
L32 33
DO5022P-333
L33 22
DO5022P-223
22
0.99
67148350 67148460
67144070 67144450
67144080 67144460
67144090 67144470
67148370 67148480
67148380 67148490
67144100 67144480
67144110 67144490
67144120 67144500
67144130 67144510
67144140 67144520
67144150 67144530
67144160 67144540
67148390 67148500
PE-53815
PE-53815-S
0.99
1.17
1.40
1.70
2.10
0.80
1.00
1.20
1.47
1.78
2.20
2.50
3.10
RL1500-68
PE-53821
PE-53822
PE-53823
PE-53821-S
-
-
PE-53822-S
PE-53823-S
-
PE-53824
PE-53825
PE-53825-S
-
PE-53824-S
-
-
-
-
-
-
-
PE-53826
PE-53827
PE-53828
PE-53829
PE-53830
PE-53831
PE-53932
PE-53826-S
PE-53827-S
PE-53828-S
PE-53829-S
PE-53830-S
PE-53831-S
PE-53932-S
-
PE-53933
PE-53933-S
2200
2000
1800
1600
1400
1200
Figure 9. RMS Current Ratings for Low ESR
Electrolytic Capacitors (typical)
1000
800
600
400
10 20 30 40 50 60 70
0
CAPACITOR VOLTAGE RATING (V)
BEIJING ESTEK ELECTRONICS CO.,LTD
12
LM2596
Address :
6A06--6A07
Rm 6A07,Changyin Office Building ,No.88,Yong Ding Road,Hai Dian District ,Beijing
Postalcode:100039
Tel: 86-010-58895780 / 81 / 82 / 83 / 84
Http://www.estek.com.cn
Fax : 010-58895793
Email:sales@estek.com.cn
REV No:01-060814
BEIJING ESTEK ELECTRONICS CO.,LTD
13
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