Datasheet LM2587T-ADJ, LM2587T-5.0, LM2587T-12, LM2587SX-ADJ, LM2587SX-3.3 Datasheet (NSC)

LM2587
SIMPLE SWITCHER

®

5A Flyback Regulator

LM2587 SIMPLE SWITCHER 5A Flyback Regulator

April 1998

General Description

The LM2587 series of regulators are monolithic integrated
circuits specifically designed for flyback, step-up (boost), and
forward converter applications. The device is available in 4
different output voltage versions: 3.3V, 5.0V,12V,andadjust­able.

Requiring a minimum number of external components,these
regulators are cost effective, and simple to use. Included in
the datasheet are typical circuits of boostandflybackregula­tors.Alsolistedare selector guides for diodes and capacitors
and a family of standard inductors and flyback transformers
designed to work with these switching regulators.

The power switch is a 5.0A NPN device that can stand-off
65V. Protecting the power switch are current and thermal
limiting circuits, and an undervoltage lockout circuit. This IC
contains a 100 kHz fixed-frequency internal oscillator that
permits the use of small magnetics. Other features include
soft start mode to reducein-rush current during start up, cur­rent mode control forimproved rejection of input voltage and
output load transients and cycle-by-cycle current limiting.An
output voltage tolerance of
ages and output load conditions, is guaranteedforthepower
supply system.

±

4%, within specified input volt-

Flyback Regulator

Features

n Requires few external components
n Family of standard inductors and transformers
n NPN output switches 5.0A, can stand off 65V
n Wide input voltage range: 4V to 40V
n Current-mode operation for improved transient

response, line regulation, and current limit

n 100 kHz switching frequency
n Internal soft-start function reduces in-rush current during

start-up

n Output transistor protected by current limit, under

voltage lockout, and thermal shutdown

n System Output Voltage Tolerance of

and load conditions

±

4%max over line

Typical Applications

n Flyback regulator
n Multiple-output regulator
n Simple boost regulator
n Forward converter

DS012316-1

Ordering Information

Package Type NSC Package Order Number

Drawing

5-Lead TO-220 Bent, Staggered Leads T05D LM2587T-3.3, LM2587T-5.0, LM2587T-12, LM2587T-ADJ
5-Lead TO-263 TS5B LM2587S-3.3, LM2587S-5.0, LM2587S-12, LM2587S-ADJ
5-Lead TO-263 Tape and Reel TS5B LM2587SX-3.3, LM2587SX-5.0, LM2587SX-12,

SIMPLE SWITCHER®and

© 1999 National Semiconductor Corporation DS012316 www.national.com

Switchers Made Simple

®

are registered trademarks of National SemiconductorCorporation.

LM2587SX-ADJ

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Input Voltage −0.4V ≤ V
Switch Voltage −0.4V ≤ V
Switch Current (Note 2) Internally Limited
Compensation Pin Voltage −0.4V ≤ V
Feedback Pin Voltage −0.4V ≤ V
Storage Temperature Range −65˚C to +150˚C
Lead Temperature

(Soldering, 10 sec.) 260˚C

COMP

FB

IN

SW

≤ 2.4V

≤ 2V

≤ 45V
≤ 65V

OUT

Maximum Junction

Temperature (Note 3) 150˚C
Power Dissipation (Note 3) Internally Limited
Minimum ESD Rating

(C=100 pF, R=1.5 kΩ 2kV

Operating Ratings

Supply Voltage 4V ≤ VIN≤ 40V
Output Switch Voltage 0V ≤ V
Output Switch Current I
Junction Temperature Range −40˚C ≤ T

≤ 60V

SW

≤ 5.0A

SW

≤ +125˚C

J

LM2587-3.3
Electrical Characteristics

Specifications with standard type face are for T
Range. Unless otherwise specified, V

IN

Symbol Parameters Conditions Typical Min Max Units

SYSTEM PARAMETERS Test Circuit of

V

OUT

∆V

OUT

∆V

IN

∆V

OUT

∆I

LOAD

η Efficiency V

Output Voltage V

/ Line Regulation V

/ Load Regulation V

I

LOAD

I

LOAD

I

LOAD

IN

IN

IN

IN

UNIQUE DEVICE PARAMETERS (Note 5)
V

∆V

REF

REF

Output Reference Measured at Feedback Pin 3.3 3.242/3.234 3.358/3.366 V
Voltage V
Reference Voltage V

COMP
IN

Line Regulation

G

M

A

VOL

Error Amp I
Transconductance V
Error Amp V
Voltage Gain R

COMP

COMP
COMP
COMP

=

25˚C, and those in bold type face apply over full Operating Temperature

J

=

5V.

Figure 2

(Note 4)

=

4V to 12V 3.3 3.17/3.14 3.43/3.46 V
=

400 mA to 1.75A

=

4V to 12V 20 50/100 mV
=

400 mA

=

12V 20 50/100 mV
=

400 mA to 1.75A

=

12V, I

=

=

4V to 40V 2.0 mV

=

=
=
=

=

1A 75

LOAD

1.0V

−30 µA to +30 µA 1.193 0.678 2.259 mmho

1.0V

0.5V to 1.6V 260 151/75 V/V

1.0 MΩ (Note 6)

%

LM2587-5.0
Electrical Characteristics

Specifications with standard type face are for T
Range. Unless otherwise specified, V

IN

Symbol Parameters Conditions Typical Min Max Units

SYSTEM PARAMETERS Test Circuit of

V

OUT

∆V

OUT

∆V

IN

∆V

OUT

∆I

LOAD

η Efficiency V

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Output Voltage V

/ Line Regulation V

/ Load Regulation V

I

LOAD

I

LOAD

I

LOAD

IN

IN

IN

IN

=

25˚C, and those in bold type face apply over full Operating Temperature

J

=

5V.

Figure 2

(Note 4)

=

4V to 12V 5.0 4.80/4.75 5.20/5.25 V
=

500 mA to 1.45A

=

4V to 12V 20 50/100 mV
=

500 mA

=

12V 20 50/100 mV
=

500 mA to 1.45A

=

12V, I

=

750 mA 80

LOAD

%

LM2587-5.0
Electrical Characteristics

Symbol Parameters Conditions Typical Min Max Units

UNIQUE DEVICE PARAMETERS (Note 5)

V

∆V

G

A

REF

REF

M

VOL

Output Reference Measured at Feedback Pin 5.0 4.913/4.900 5.088/5.100 V
Voltage V
Reference Voltage V
Line Regulation
Error Amp I
Transconductance V
Error Amp V
Voltage Gain R

(Continued)

=

1.0V

COMP

=

4V to 40V 3.3 mV

IN

=

−30 µA to +30 µA 0.750 0.447 1.491 mmho

COMP

=

1.0V

COMP

=

0.5V to 1.6V 165 99/49 V/V

COMP

=

1.0 MΩ (Note 6)

COMP

LM2587-12
Electrical Characteristics

Specifications with standard type face are for T
Range. Unless otherwise specified, V

IN

Symbol Parameters Conditions Typical Min Max Units

SYSTEM PARAMETERS Test Circuit of

V

OUT

∆V

OUT

∆V

IN

∆V

OUT

∆I

LOAD

η Efficiency V

Output Voltage V

/ Line Regulation V

/ Load Regulation V

I

I

I

IN

LOAD

IN

LOAD

IN

LOAD

IN

UNIQUE DEVICE PARAMETERS (Note 5)
V

∆V

REF

REF

Output Reference Measured at Feedback Pin 12.0 11.79/11.76 12.21/12.24 V
Voltage V
Reference Voltage V

COMP
IN

Line Regulation

G

M

A

VOL

Error Amp I
Transconductance V
Error Amp V
Voltage Gain R

COMP

COMP
COMP
COMP

=

25˚C, and those in bold type face apply over full Operating Temperature

J

=

5V.

Figure 3

(Note 4)

=

4V to 10V 12.0 11.52/11.40 12.48/12.60 V
=

300 mA to 1.2A

=

4V to 10V 20 100/200 mV
=

300 mA

=

10V 20 100/200 mV
=

300 mA to 1.2A

=

10V, I

=

=

4V to 40V 7.8 mV

=

=
=
=

=

1A 90

LOAD

1.0V

−30 µA to +30 µA 0.328 0.186 0.621 mmho

1.0V

0.5V to 1.6V 70 41/21 V/V

1.0 MΩ (Note 6)

%

LM2587-ADJ
Electrical Characteristics

Specifications with standard type face are for T
Range. Unless otherwise specified, V

IN

Symbol Parameters Conditions Typical Min Max Units

SYSTEM PARAMETERS Test Circuit of

V

OUT

∆V

OUT

∆V

IN

∆V

OUT

∆I

LOAD

η Efficiency V

Output Voltage V

/ Line Regulation V

/ Load Regulation V

I

LOAD

I

LOAD

I

LOAD

IN

IN

IN

IN

=

25˚C, and those in bold type face apply over full Operating Temperature

J

=

5V.

Figure 3

(Note 4)

=

4V to 10V 12.0 11.52/11.40 12.48/12.60 V
=

300 mA to 1.2A

=

4V to 10V 20 100/200 mV
=

300 mA

=

10V 20 100/200 mV
=

300 mA to 1.2A

=

10V, I

LOAD

=

1A 90

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%

LM2587-ADJ
Electrical Characteristics

Symbol Parameters Conditions Typical Min Max Units

UNIQUE DEVICE PARAMETERS (Note 5)

V

∆V

G

A

I

REF

REF

M

VOL

B

Output Reference Measured at Feedback Pin 1.230 1.208/1.205 1.252/1.255 V
Voltage V
Reference Voltage V
Line Regulation
Error Amp I
Transconductance V
Error Amp V
Voltage Gain R
Error Amp V
Input Bias Current

(Continued)

=

1.0V

COMP

=

4V to 40V 1.5 mV

IN

=

−30 µA to +30 µA 3.200 1.800 6.000 mmho

COMP

=

1.0V

COMP

=

0.5V to 1.6V 670 400/200 V/V

COMP

=

1.0 MΩ (Note 6)

COMP

=

1.0V 125 425/600 nA

COMP

All Output Voltage Versions
Electrical Characteristics

Specifications with standard type face are for T

Range. Unless otherwise specified, V

Symbol Parameters Conditions Typical Min Max Units

I

S

V

UV

f

O

f

SC

V

EAO

I

EAO

I

SS

D Maximum Duty Cycle R

I

L

V

SUS

V

SAT

I

CL

Input Supply Current (Switch Off) 11 15.5/16.5 mA

Input Supply R
Undervoltage Lockout
Oscillator Frequency Measured at Switch Pin

Short-Circuit Measured at Switch Pin
Frequency R

Error Amplifier Upper Limit 2.8 2.6/2.4 V
Output Swing (Note 7)

Error Amp (Note 9)
Output Current 165 110/70 260/320 µA
(Source or Sink)
Soft Start Current V

Switch Leakage Switch Off 15 300/600 µA
Current V
Switch Sustaining dV/dT=1.5V/ns 65 V
Voltage
Switch Saturation I
Voltage
NPN Switch 6.5 5.0 9.5 A
Current Limit

(Note 5)

=

25˚C, and those in bold type face apply over full Operating Temperature

J

=

5V.

IN

(Note 8)

=

I

SWITCH

R
V

V

3.0A 85 140 165 mA

=

100Ω 3.30 3.05 3.75 V

LOAD

=

100Ω 100 85/75 115/125 kHz

LOAD

=

1.0V

COMP

=

100Ω 25 kHz

LOAD
FEEDBACK

=

1.15V

Lower Limit 0.25 0.40/0.55 V
(Note 8)

=

FEEDBACK

V

COMP
LOAD

0.92V 11.0 8.0/7.0 17.0/19.0 µA

=

1.0V

=

100Ω 98 93/90

(Note 7)

=

SWITCH

SWITCH

60V

=

5.0A 0.7 1.1/1.4 V

%

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All Output Voltage Versions
Electrical Characteristics

Symbol Parameters Conditions Typical Min Max Units
COMMON DEVICE PARAMETERS (Note 4)

θ

JA

θ

JA

θ

JC

θ

JA

θ

JA

θ

JA

θ

JC

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions the device is intended to
be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical
Characteristics.

Note 2: Note that switch current and output current are not identical in a step-up regulator. Output current cannot be internally limited when the LM2587 is used as
a step-up regulator. To prevent damage to the switch, the output current must be externally limited to 5A. However, output current is internally limited when the
LM2587 is used as a flyback regulator (see the Application Hints section for more information).

Note 3: The junction temperature of the device (T
dissipation of the device (P

(MAX)

allowable power dissipation, derate the maximum junction temperature — this ensures a margin of safety in the thermal design.
Note 4: External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the LM2587 is used as

shown in
Note 5: All room temperature limits are 100%production tested, and all limits at temperature extremes are guaranteed via correlation using standard Statistical Qual-

ity Control (SQC) methods.

Note 6: A 1.0 MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuringA
Note 7: Tomeasure this parameter, the feedback voltage is set to a low value, depending on the output version of the device, to force the error amplifier output high.

Adj: V
Note 8: Tomeasure this parameter, the feedback voltage is set to a high value, depending on the output version of the device, to force the error amplifier output low.

Adj: V
Note 9: Tomeasure the worst-case error amplifier output current, the LM2587 is tested with the feedback voltage set to its low value (specified in Note 7) and at its

high value (specified in Note 8).
Note 10: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically,with

board with minimum copper area.
Note 11: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically,with

containing approximately 4 square inches of (1oz.) copper area surrounding the leads.
Note 12: Junction to ambient thermal resistance for the 5 lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the same size as the

TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 13: Junction to ambient thermal resistance for the 5 leadTO-263 mounted horizontally against a PC board areaof 0.4896 square inches (3.6 times the area

of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.
Note 14: Junction to ambient thermal resistance for the 5 lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square inches (7.4 times the

area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.Additional copper area will reduce thermal resistance further. See the thermal model in Switchers Made
Simple

Thermal Resistance T Package, Junction to Ambient

). A thermal shutdown will occur if the temperature exceedsthe maximum junction temperature of the device: PDx θJA+T

and

D

Figure 3

, system performance will be as specified by the system parameters.

=

2.81V; 5.0V: V

FB

=

3.80V; 5.0V: V

FB

. For a safe thermal design, check that the maximum power dissipated by the device is less than: PD≤ [T

Figure 2

=

1.05V; 3.3V: V

FB

=

1.41V; 3.3V: V

FB

®

software.

(Note 5) (Continued)

65

(Note 10)
T Package, Junction to Ambient

45

(Note 11)
T Package, Junction to Case 2
S Package, Junction to Ambient

56

(Note 12)
S Package, Junction to Ambient

35

(Note 13)
S Package, Junction to Ambient

26

(Note 14)
S Package, Junction to Case 2

) is a function of the ambient temperature (TA), the junction-to-ambient thermal resistance (θJA), and the power

J

)]/θJA. When calculating the maximum

.

VOL

1

⁄2inch leads in a socket, or on a PC

1

⁄2inch leads soldered to a PC board

=

FB

=

FB

4.25V; 12V: V

5.75V; 12V: V

J(MAX)−TA(MAX)

=

10.20V.

FB

=

13.80V.

FB

˚C/W

A(MAX)

≥ T

-

J

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Typical Performance Characteristics

Supply Current
vs Temperature

Supply Current
vs Switch Current

Switch Saturation
Voltage vs Temperature

DS012316-48

DS012316-51

Reference Voltage
vs Temperature

Current Limit
vs Temperature

Switch Transconductance
vs Temperature

DS012316-49

DS012316-52

∆Reference Voltage
vs Supply Voltage

DS012316-50

Feedback Pin Bias
Current vs Temperature

DS012316-53

Oscillator Frequency
vs Temperature

DS012316-54

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DS012316-55

DS012316-56

Typical Performance Characteristics (Continued)

Error Amp Transconductance
vs Temperature

DS012316-57

Connection Diagrams

Bent, Staggered Leads

5-Lead TO-220 (T)

Top View

5-Lead TO-263 (S)

Top View

Error Amp Voltage
Gain vs Temperature

DS012316-58

Bent, Staggered Leads

DS012316-3

Order Number LM2587T-3.3, LM2587T-5.0,

LM2587T-12 or LM2587T-ADJ

See NS Package Number T05D

Short Circuit Frequency
vs Temperature

DS012316-59

5-Lead TO-220 (T)

Side View

DS012316-4

5-Lead TO-263 (S)

Side View

DS012316-5

Order Number LM2587S-3.3, LM2587S-5.0,

LM2587S-12 or LM2587S-ADJ

See NS Package Number TS5B

DS012316-6

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Block Diagram

For Fixed Versions

3.3V, R1=3.4k, R2=2k
5V, R1=6.15k, R2=2k
12V, R1=8.73k, R2=1k
For Adj. Version
R1=Short (0Ω), R2=Open

DS012316-7

FIGURE 1.

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Test Circuits

C

— 100 µF, 25V Aluminum Electrolytic

IN1

C

— 0.1 µF Ceramic

IN2

T— 22 µH, 1:1 Schott#67141450
D— 1N5820

— 680 µF, 16V Aluminum Electrolytic

C

OUT

CC— 0.47 µF Ceramic
RC—2k

C

— 100 µF, 25V Aluminum Electrolytic

IN1

C

— 0.1 µF Ceramic

IN2

L— 15 µH, Renco#RL-5472-5
D— 1N5820
C

— 680 µF, 16V Aluminum Electrolytic

OUT

CC— 0.47 µF Ceramic
RC—2k
For 12V Devices: R
For ADJ Devices: R

=

Short (0Ω) and R

1

=

48.75k,

1

=

Open

2

±

0.1%and R2=5.62k,±1

DS012316-8

FIGURE 2. LM2587-3.3 and LM2587-5.0

DS012316-9

%

FIGURE 3. LM2587-12 and LM2587-ADJ

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Flyback Regulator Operation

The LM2587 is ideally suited for use in the flyback regulator
topology. The flyback regulator can produce a single output
voltage, such as the one shown in
put voltages. In

Figure 4

, the flyback regulator generates an
output voltage that is inside the range of the input voltage.
This feature is unique to flyback regulators and cannot be
duplicated with buck or boost regulators.

The operation of a flyback regulator is as follows (refer to

Figure 4

): when the switch is on, current flows through the
primary winding of the transformer, T1, storing energy in the
magnetic field of the transformer. Note that the primary and
secondary windings are out of phase, so no current flows
through the secondary when current flows through the pri­mary. When the switch turns off, the magnetic field col-

Figure 4

, or multiple out-

lapses, reversing the voltage polarityof theprimary and sec­ondary windings. Now rectifier D1 is forward biased and
current flows through it, releasing the energy stored in the
transformer. This produces voltage at the output.

The output voltage is controlled by modulating the peak
switch current. This is done by feeding back a portion of the
output voltage to the error amp, which amplifies the differ­ence between the feedback voltageand a 1.230Vreference.
The error amp output voltage is compared to a rampvoltage
proportional to the switch current (i.e., inductor current dur­ing the switch on time). The comparator terminates the
switch on time when the two voltages are equal, thereby
controlling the peak switch current to maintain a constant
output voltage.

As shown in
regulator are shown in

Figure 4

, the LM2587 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this

Figure 5

. Typical Performance Characteristics observed during the operation of this circuit are shown in

FIGURE 4. 12V Flyback Regulator Design Example

Typical Performance Characteristics

A: Switch Voltage, 10 V/div
B: Switch Current, 5 A/div
C: Output Rectifier Current, 5A/div
D: Output Ripple Voltage, 100 mV/div

AC-Coupled

Horizontal: 2 µs/div

FIGURE 5. Switching Waveforms

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DS012316-11

DS012316-10

Figure 6

.

Typical Performance Characteristics (Continued)

FIGURE 6. V

Load Current Step Response

OUT

Typical Flyback Regulator Applications

Figures 7, 8, 9, 11, 12

show six typical flyback applications,
varying from single output to triple output. Each drawing con­tains the partnumber(s) and manufacturer(s) for every com­ponent except the transformer. For the transformer part
numbers and manufacturers names, see the table in

Figure

13

. For applications with different output
voltages— requiring the LM2587-ADJ —or different output
configurations that do not match the standard configurations,
refer to the

DS012316-12

Switchers Made Simple

software.

FIGURE 7. Single-Output Flyback Regulator

DS012316-13

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Typical Flyback Regulator Applications (Continued)

FIGURE 8. Single-Output Flyback Regulator

DS012316-14

FIGURE 9. Single-Output Flyback Regulator

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DS012316-15

Typical Flyback Regulator Applications (Continued)

FIGURE 10. Dual-Output Flyback Regulator

DS012316-16

FIGURE 11. Dual-Output Flyback Regulator

DS012316-17

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Typical Flyback Regulator Applications (Continued)

DS012316-18

FIGURE 12. Triple-Output Flyback Regulator

Transformer Selection (T)

Figure 13

each transformer, as well as the output voltages, input voltage ranges, and the maximum load currents for each circuit.

lists the standard transformers available forflyback regulator applications.Included in thetable are theturns ratio(s) for

Applications

Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

Transformers T1 T1 T1 T2 T3 T4

V

IN

V

OUT1

I

(Max) 1.8A 1.4A 1.2A 0.3A 1A 2.5A

OUT1

N

1

V

OUT2

I

(Max) 0.3A 1A 0.5A

OUT2

N

2

V

OUT3

I

(Max) 0.5A

OUT3

N

3

4V–6V 4V–6V 8V–16V 4V–6V 18V–36V 18V–36V

3.3V 5V 12V 12V 12V 5V

1 1 1 2.5 0.8 0.35

−12V −12V 12V

2.5 0.8 0.8

FIGURE 13. Transformer Selection Table

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−12V

0.8

Typical Flyback Regulator Applications (Continued)

Transformer

Type

Coilcraft Coilcraft (Note 15) Pulse (Note 16) Renco Schott

Manufacturers’ Part Numbers

(Note 15) Surface Mount Surface Mount (Note 17) (Note 18)
T1 Q4434-B Q4435-B PE-68411 RL-5530 67141450
T2 Q4337-B Q4436-B PE-68412 RL-5531 67140860
T3 Q4343-B — PE-68421 RL-5534 67140920
T4 Q4344-B — PE-68422 RL-5535 67140930

Note 15: Coilcraft Inc.,: Phone: [phone]
1102 Silver Lake Road, Cary, IL 60013: Fax: [phone]
Note 16: Pulse Engineering Inc.,: Phone: [phone]
12220 World Trade Drive, San Diego, CA92128: Fax: [phone]
Note 17: Renco Electronics Inc.,: Phone: [phone]
60 Jeffryn Blvd. East, Deer Park, NY 11729: Fax: [phone]
Note 18: Schott Corp.,: Phone: [phone]
1000 Parkers Lane Road, Wayzata, MN 55391: Fax: [phone]

FIGURE 14. Transformer Manufacturer Guide

Transformer Footprints

Figures 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31

listed in

Figure 14

.

T1

DS012316-30

and

Figure 32

show the footprints of each transformer,

T4

Top View

FIGURE 15. Coilcraft Q4434-B

T2

Top View

FIGURE 16. Coilcraft Q4337-B

T3

Top View

FIGURE 17. Coilcraft Q4343-B

DS012316-33

Top View

FIGURE 18. Coilcraft Q4344-B

T1

DS012316-31

DS012316-34

Top View

FIGURE 19. Coilcraft Q4435-B

(Surface Mount)

DS012316-32

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Typical Flyback Regulator
Applications

(Continued)

T2

T4

Top View

FIGURE 20. Coilcraft Q4436-B

(Surface Mount)

T1

Top View

FIGURE 21. Pulse PE-68411

(Surface Mount)

T2

Top View

FIGURE 22. Pulse PE-68412

(Surface Mount)

DS012316-35

DS012316-36

DS012316-37

DS012316-39

Top View

FIGURE 24. Pulse PE-68422

(Surface Mount)

T1

DS012316-40

Top View

FIGURE 25. Renco RL-5530

T2

DS012316-41

Top View

FIGURE 26. Renco RL-5531

T3

T3

DS012316-38

Top View

FIGURE 23. Pulse PE-68421

(Surface Mount)

www.national.com 16

DS012316-46

Top View

FIGURE 27. Renco RL-5534

Typical Flyback Regulator
Applications

(Continued)

T4

Top View

FIGURE 28. Renco RL-5535

T1

Top View

FIGURE 29. Schott 67141450

T2

T3

DS012316-45

Top View

FIGURE 31. Schott 67140920

T4

DS012316-42

DS012316-47

Top View

FIGURE 32. Schott 67140930

DS012316-43

Top View

FIGURE 30. Schott 67140860

DS012316-44

www.national.com17

Step-Up (Boost) Regulator Operation

Figure 33

regulator. This is a switching regulator that produces an out­put voltage greater than the input supply voltage.

A brief explanation of how the LM2587 Boost Regulator
works is as follows (refer to
switch turns on, the inductor current ramps up at the rate of
V

shows the LM2587 used as a step-up (boost)

Figure 33

/L, storing energy in the inductor. When the switch turns

IN

). When the NPN

off, the lower end ofthe inductorflies above V
its current through diode (D)into theoutput capacitor (C
at a rate of (V
tor during theswitch on time is transferred to the output dur-

)/L. Thus, energy storedin theinduc-

OUT−VIN

, discharging

IN

OUT

ing the switch off time. The output voltage is controlled by
adjusting the peak switch current, as described in the flyback
regulator section.

)

By adding a small number of external components (as shown in
the applied input voltage. The switching waveforms observed during the operation of this circuit are shown in
shown in

Figure 35

.

Figure 33

), the LM2587 can be used to produce a regulated output voltage that is greater than

FIGURE 33. 12V Boost Regulator

Typical Performance Characteristics

A: Switch Voltage, 10 V/div
B: Switch Current, 5 A/div
C: Inductor Current, 5 A/div
D: Output Ripple Voltage,

100 mV/div, AC-Coupled

Horizontal: 2 µs/div

FIGURE 34. Switching Waveforms

DS012316-20

DS012316-19

Figure 34

. Typical performance of this regulator is

www.national.com 18

Typical Performance Characteristics (Continued)

FIGURE 35. V

Response to Load Current Step

OUT

Typical Boost Regulator Applications

Figure 36

and

Figures 38, 39

and

Figure 40

show four typical
boost applications)—one fixed and three using the adjust­able version of the LM2587. Each drawing contains the part
number(s) and manufacturer(s) for every component. For

the fixed 12V output application, the part numbers and
manufacturers’ names for the inductor are listedin a table in

Figure 40

fer to the

DS012316-21

. For applications with different output voltages, re-

Switchers Made Simple

software.

FIGURE 36. +5V to +12V Boost Regulator

Figure 37

of

contains a table of standard inductors, by part number and corresponding manufacturer, for the fixed output regulator

Figure 36

.

Coilcraft

(Note 19)

Pulse

(Note 20)

R4793-A PE-53900 RL-5472-5 67146520

Note 19: Coilcraft Inc.,: Phone: [phone]
1102 Silver Lake Road, Cary, IL 60013: Fax: [phone]
Note 20: Pulse Engineering Inc.,: Phone: [phone]
12220 World Trade Drive, San Diego, CA92128: Fax: [phone]
Note 21: Renco Electronics Inc.,: Phone: [phone]
60 Jeffryn Blvd. East, Deer Park, NY 11729: Fax: [phone]
Note 22: Schott Corp.,: Phone: [phone]
1000 Parkers Lane Road, Wayzata, MN 55391: Fax: [phone]

FIGURE 37. Inductor Selection Table

Renco

(Note 21)

DS012316-22

Schott

(Note 22)

www.national.com19

Typical Boost Regulator Applications (Continued)

FIGURE 38. +12V to +24V Boost Regulator

FIGURE 39. +24V to +36V Boost Regulator

DS012316-23

DS012316-24

*

The LM2587 will require a heat sink in these applications. The size of the heat sink will depend on the maximum ambient temperature. To calculate the thermal

resistance of the IC and the size of the heat sink needed, see the “Heat Sink/Thermal Considerations” section in the Application Hints.

DS012316-25

FIGURE 40. +24V to +48V Boost Regulator

www.national.com 20

Application Hints

FIGURE 41. Boost Regulator

PROGRAMMING OUTPUT VOLTAGE
(SELECTING R

Referring to theadjustable regulator in
voltage is programmed bythe resistorsR
lowing formula:

V

OUT

Resistors R
it can be compared with the 1.23V internal reference. With
R

between 1k and 5k, R1is:

2

=

R

1

For best temperature coefficient and stability with time, use
1%metal film resistors.

SHORT CIRCUIT CONDITION

Due to the inherent natureof boost regulators,when the out­put is shorted (see
input, through the inductor and the diode, to the output, by­passing the switch. The current limit of the switch
limit the output current for the entire circuit. To protect the
load and prevent damage to the switch, the current must be
externally limited, either by the input supply or at the output
with an external current limitcircuit. Theexternal limit should
be set to the maximum switch current of the device,which is
5A.

In a flyback regulator application (
dard transformers, the LM2587 will survive a short circuit to

AND R2)

1

Figure 41

and R2by the fol-

1

=

(1+R1/R2) where V

V

REF

and R2divide the output voltage down so that

1

R

2(VOUT/VREF

− 1) where V

Figure 41

), current flows directlyfrom the

Figure 42

REF

REF

), using the stan-

, the output

=

1.23V

=

1.23V

does not

DS012316-26

the main output. When the outputvoltage drops to80%of its
nominal value, the frequency will drop to 25 kHz. With a
lower frequency, off times are larger. With the longer off
times, the transformer can release all of its stored energy be­fore the switch turnsback on.Hence, theswitch turnson ini­tially with zero current at its collector. In this condition, the
switch current limit will limit the peak current, saving the de­vice.

FLYBACK REGULATOR INPUT CAPACITORS

A flyback regulator draws discontinuous pulses of current
from the input supply.Therefore, there are twoinput capaci­tors needed in a flyback regulator; one for energy storage
and one for filtering (see

Figure 42

). Both are required due to
the inherent operation of a flyback regulator. To keep a
stable or constant voltage supply to the LM2587, a storage
capacitor (≥100 µF) isrequired. Ifthe inputsource is a reciti­fied DC supply and/or the application has a wide tempera­ture range, the required rms current rating of the capacitor
might be very large. This means a larger value of capaci­tance or a higher voltage rating will be needed of the input
capacitor. The storage capacitor will also attenuate noise
which may interfere with other circuits connected to the
same input supply voltage.

www.national.com21

Application Hints (Continued)

FIGURE 42. Flyback Regulator

In addition, a small bypass capacitor is required due to the
noise generated by the inputcurrent pulses.Toeliminate the
noise, insert a 1.0 µF ceramic capacitor between V
ground as close as possible to the device.

SWITCH VOLTAGE LIMITS

In a flyback regulator, the maximum steady-statevoltage ap­pearing at theswitch, when it is off, isset by the transformer
turns ratio, N, the output voltage, V
put voltage, V

where V
and is 0.5V for Schottkydiodes and0.8V forultra-fast recov-

(Max):

IN

=

V

SW(OFF)

is the forward biased voltage of the output diode,

F

(Max) + (V

V

IN

, and the maximum in-

OUT

)/N

OUT+VF

ery diodes (typically). In certain circuits, there exists a volt­age spike, V
age (see

, superimposed on top of the steady-state volt-

LL

Figure 5

, waveformA). Usually, this voltage spike is
caused by the transformer leakage inductance and/or the
output rectifier recovery time. To “clamp” the voltage at the
switch from exceeding its maximum value, a transient sup­pressor in series with a diode is inserted across the trans­former primary (as shown inthe circuiton thefront pageand
other flyback regulator circuits throughout the datasheet).
The schematic in

Figure 42

shows another method of clamp­ing the switch voltage. A single voltage transient suppressor
(the SA51A) is inserted at the switch pin. This method
clamps the total voltage across the switch, not just the volt­age across the primary.

If poor circuit layout techniques are used (see the “Circuit
Layout Guideline” section), negative voltage transients may
appear on the Switch pin (pin 4).Applying a negative voltage
(with respect to the IC’s ground) to any monolithic IC pin
causes erratic and unpredictable operation of that IC. This
holds true for the LM2587 IC aswell. When usedin a flyback
regulator, the voltage at the Switch pin (pin 4) can go nega­tive when the switch turns on. The “ringing” voltage at the
switch pin is caused by the output diode capacitanceand the
transformer leakage inductance forminga resonant circuit at
the secondary(ies). The resonant circuit generates the“ring-

and

IN

DS012316-27

ing” voltage, which gets reflected back through the trans­former to the switch pin. There are two common methods to
avoid this problem. Oneis toadd anRC snubberaround the
output rectifier(s), as in

Figure 42

. The values of the resistor
and the capacitor must be chosen so that the voltage at the
Switch pin does not drop below −0.4V. The resistor may
range in value between10Ω and1kΩ, andthe capacitorwill
vary from 0.001µF to 0.1 µF.Adding a snubber will (slightly)
reduce the efficiency of the overall circuit.

The other method to reduce or eliminatethe “ringing” is to in­sert a Schottky diode clamp between pins 4 and 3 (ground),
also shown in

Figure 42

. This prevents the voltage at pin 4
from dropping below −0.4V.The reversevoltage rating of the
diode must be greater than the switch off voltage.

DS012316-28

FIGURE 43. Input Line Filter

OUTPUT VOLTAGE LIMITATIONS

The maximum output voltage of a boost regulator is the
maximum switch voltage minus a diode drop. In a flyback
regulator, the maximum output voltage is determined by the
turns ratio, N, and the duty cycle, D, by the equation:

≈ NxVINxD/(1−D)

V

OUT

www.national.com 22

Application Hints (Continued)

The duty cycle of a flyback regulator is determined bythe fol­lowing equation:

Theoretically, the maximum output voltage can be as large
as desired— just keep increasing the turnsratio of thetrans­former. However, there exists some physical limitations that
prevent the turns ratio, and thus the output voltage, from in­creasing to infinity. The physical limitations are capacitances
and inductances in the LM2587 switch, the output diode(s),
and the transformer— such as reverse recovery time of the
output diode (mentioned above).

NOISY INPUT LINE CONDITION)

A small, low-pass RC filtershould be used at the inputpin of
the LM2587 if the input voltage hasan unusual largeamount
of transient noise, such as with aninput switch thatbounces.
The circuit in

Figure 43

demonstrates the layout of the filter,

with the capacitor placed from the input pin to ground and
the resistor placed between the input supply and the input
pin. Note that the values of R
matic are good enough for most applications, but some read-

and CINshown in the sche-

IN

justing might be required for a particular application. If effi­ciency is a major concern, replace the resistor with a small
inductor (say 10 µH and rated at 100 mA).

STABILITY

All current-mode controlled regulators can suffer from an in­stability, known as subharmonic oscillation, if they operate
with a duty cycle above 50%. To eliminate subharmonic os­cillations, a minimum value of inductance is required to en­sure stability for all boost and flyback regulators. The mini­mum inductance is given by:

where V
found in the Characteristic Curves.

is the switch saturation voltage and can be

SAT

FIGURE 44. Circuit Board Layout

CIRCUIT LAYOUT GUIDELINES

As in any switching regulator, layout is very important. Rap­idly switching currents associated with wiring inductance
generate voltage transients which can cause problems. For
minimal inductance and ground loops,keep thelength of the
leads and traces as short as possible. Use single point
grounding or ground plane construction for best results.
Separate the signal grounds from the power grounds (as in­dicated in

Figure 44

). When using the Adjustable version,
physically locate the programming resistors as near the
regulator IC as possible, to keep the sensitive feedback wir­ing short.

HEAT SINK/THERMAL CONSIDERATIONS

In many cases, no heat sinkis required to keep the LM2587
junction temperature within theallowed operating range. For
each application, to determine whetheror not aheat sink will
be required, the following must be identified:

1) Maximum ambient temperature (in the application).

2) Maximum regulator power dissipation (in the application).

DS012316-29

3) Maximum allowed junction temperature (125˚C for the
LM2587). For a safe, conservative design, a temperature ap­proximately 15˚C cooler than the maximum junction tem­perature should be selected (110˚C).

4) LM2587 package thermal resistances θ
in the Electrical Characteristics).

Total power dissipated (P
as follows:

) by the LM2587 can be estimated

D

and θJC(given

JA

Boost:

VINis the minimum input voltage,V
N is the transformer turns ratio, D is the duty cycle, and I
is the maximum load current (and∑I
maximum load currents for multiple-output flyback regula-

is the output voltage,

OUT

is the sum of the

LOAD

LOAD

tors). The duty cycle is given by:

www.national.com23

Application Hints (Continued)

Boost:

where VFis the forward biased voltage of the diode and is
typically 0.5V for Schottky diodes and 0.8V for fast recovery
diodes. V
found in the Characteristic Curves.

When no heat sink is used, the junction temperature rise is:

Adding the junction temperature rise to the maximum ambi­ent temperature gives the actualoperating junction tempera­ture:

If the operating junction temperature exceeds the maximum
junction temperatue in item 3 above, then a heat sink is re­quired. When using a heat sink, the junction temperature rise
can be determined by the following:

Again, the operating junction temperature will be:

As before, if the maximum junction temperature is exceeded,
a larger heat sink is required (one that has a lower thermal
resistance).

is the switch saturation voltage and can be

SAT

=

∆T

∆T

T

=

x(θJC+ θ

P

J

D

T

x θJA.

P

J

D

=

J

=

J

∆T

∆T

J+TA

Interface

J+TA

.

+ θ

Heat Sink

)

Included in the

Switchers Made Simple

design software is
a more precise (non-linear) thermal model that can be used
to determine junction temperature with different input-output
parameters or different component values.It can also calcu­late the heat sink thermal resistancerequired to maintainthe
regulator junction temperature below the maximum operat­ing temperature.

To further simplify the flyback regulator design procedure,
National Semiconductor is making available computer de­sign software. Switchers Made Simple software is available

1

ona(3

⁄2") diskette for IBM compatable computers from a
National Semiconductor sales office in your area or the Na­tional Semiconductor Customer Response Center
(1-800-272-9959).

European Magnetic Vendor
Contacts

Please contact the following addresses for details of local
distributors or representatives:

Coilcraft

21 Napier Place
Wardpark North

Cumbernauld, Scotland G68 0LL
Phone: [phone]
Fax: [phone]

Pulse Engineering

Dunmore Road
Tuam

Co. Galway, Ireland
Phone: [phone]
Fax: [phone]

www.national.com 24

Physical Dimensions inches (millimeters) unless otherwise noted

Order Number LM2587T-3.3, LM2587T-5.0,

LM2587T-12 or LM2587T-ADJ

NS Package Number T05D

www.national.com25

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LM2587 SIMPLE SWITCHER 5A Flyback Regulator

Order Number LM2587S-3.3, LM2587S-5.0,

LM2587S-12 or LM2587S-ADJ

NS Package Number TS5B

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1. Life support devices or systems are devices or sys­tems which, (a) are intended for surgical implant into
the body, or (b) support orsustain life, and whosefail­ure to perform when properly used in accordance

2. A critical component is any component of a life support
device or system whose failure to perform can be rea­sonably expected to causethe failureof thelife support
device or system, or to affectits safety oreffectiveness.

with instructions for use provided in the labeling, can
be reasonably expected to result ina significant injury
to the user.

National Semiconductor
Corporation

Americas
Tel: [phone]
Fax: [phone]
Email: [e-mail]

www.national.com

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right atany time without notice to change said circuitry and specifications.

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