Datasheet LM2588T-ADJ, LM2588T-5.0, LM2588T-12, LM2588SX-ADJ, LM2588SX-5.0 Datasheet (NSC)

LM2588
SIMPLE SWITCHER
Shutdown

®

5A Flyback Regulator with

LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown

April 1998

General Description

The LM2588 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 an adjustable frequency oscillator that can be pro­grammed up to 200kHz. The oscillator can also be synchro­nized with other devices, so that multiple devices can oper­ate at the same switching frequency.

Other features includesoft start mode to reduce in-rush cur­rent during start up, and current mode control for improved
rejection of input voltage and output load transients and
cycle-by-cycle current limiting. The device also has a shut­down pin, so that it can be turned off externally. An output
voltage tolerance of
output load conditions, is guaranteed for the power supply
system.

±

4%, within specified input voltages and

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 Adjustable switching frequency: 100 kHz to 200 kHz
n External shutdown capability
n Draws less than 60 µA when shut down
n Frequency synchronization
n Current-mode operation for improved transient

response, line regulation, and current limit

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 Forward converter
n Multiple-output regulator
n Simple boost regulator

DS012420-1

SIMPLE SWITCHER®and

© 1999 National Semiconductor Corporation DS012420 www.national.com

Switchers Made Simple

®

are registered trademarks of National SemiconductorCorporation.

Ordering Information

Package Type NSC Package Order Number

Drawing

7-Lead TO-220 Bent, Staggered Leads TA07B LM2588T-3.3, LM2588T-5.0, LM2588T-12, LM2588T-ADJ
7-Lead TO-263 TS7B LM2588S-3.3, LM2588S-5.0, LM2588S-12, LM2588S-ADJ
7-Lead TO-263 Tape and Reel TS7B LM2588SX-3.3, LM2588SX-5.0, LM2588SX-12,

LM2588SX-ADJ

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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
ON /OFF Pin Voltage −0.4V ≤ VSH≤ 6V
Sync Pin Voltage −0.4V ≤ V
Power Dissipation (Note 3) Internally Limited
Storage Temperature Range −65˚C to +150˚C

COMP

FB

IN

SW

≤ 2V

SYNC

≤ 45V
≤ 65V

≤ 2.4V

OUT

≤ 2V

Lead Temperature

(Soldering, 10 sec.) 260˚C

Maximum Junction Temperature

(Note 3) 150˚C

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

LM2588-3.3
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 1

(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)

%

LM2588-5.0
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

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

REF

Output Reference Measured at Feedback Pin 5.0 4.913/4.900 5.088/5.100 V
Voltage V

COMP

=

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

J

=

5V.

Figure 1

(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

=

1.0V

=

750 mA 80

LOAD

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%

LM2588-5.0
Electrical Characteristics

Specifications with standard type face are for T

Range. Unless otherwise specified, V

Symbol Parameters Conditions Typical Min Max Units

UNIQUE DEVICE PARAMETERS (Note 5)

∆V

G

A

REF

M

VOL

Reference Voltage V
Line Regulation
Error Amp I
Transconductance V
Error Amp V
Voltage Gain R

(Continued)

=

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

J

=

5V.

IN

=

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

LM2588-12
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

LOAD

I

LOAD

I

LOAD

IN

IN

IN

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 2

(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)

%

LM2588-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

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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 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

=

1A 90

LOAD

%

LM2588-ADJ
Electrical Characteristics

Specifications with standard type face are for T

Range. Unless otherwise specified, V
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)

=

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

J

=

5V.

IN

=

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

I

S/D

V

UV

f

O

f

SC

V

EAO

I

EAO

I

SS

D

MAX

I

L

V

SUS

Input Supply Current Switch Off 11 15.5/16.5 mA

Shutdown Input V
Supply Current
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

Maximum Duty
Cycle

Switch Leakage Switch Off 15 300/600 µA
Current V
Switch Sustaining

Voltage

(Note 5)

=

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

J

=

5V.

IN

(Note 8)

=

I

SWITCH

R

3.0A 85 140/165 mA

=

3V 16 100/300 µA

SH

=

100Ω 3.30 3.05 3.75 V

LOAD

LOAD

=

100Ω,V

=

1.0V 100 85/75 115/125 kHz

COMP

Freq. Adj. Pin Open (Pin 1)

=

R

22 kΩ 200 kHz

SET

=

100Ω 25 kHz

LOAD

V

FEEDBACK

=

1.15V

Lower Limit 0.25 0.40/0.55 V
(Note 8)

=

FEEDBACK

V

COMP

R

LOAD

0.92V 11.0 8.0/7.0 17.0/19.0 µA

=

1.0V

=

100Ω 98 93/90

(Note 7)

=

SWITCH

60V

dV/dT=1.5V/ns 65 V

%

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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

V

SAT

I

CL

V

STH

I

SYNC

V

SHTH

I

SH

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.These ratings apply when the current is limited to less than 1.2 mA
for pins 1, 2, 3, and 6. Operating ratings indicateconditions for which the device isintended to be functional, but deviceparameter 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 LM2588 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
LM2588 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 LM2588 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

and the switch on.
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

and the switch off.
Note 9: Tomeasure the worst-case error amplifier output current,the LM2588 is tested with the feedbackvoltage set to its low value (specifiedin (Note 7)) andat

its high value (specified in (Note 8)).
Note 10: When testing the minimum value, do not sink current from this pin — isolate it with a diode. If current is drawn from this pin, the frequency adjust circuit will

begin operation (see
Note 11: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with

board with minimum copper area.
Note 12: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically,with

containing approximately 4 square inches of (1 oz.) copper area surrounding the leads.
Note 13: Junction to ambient thermal resistance for the 7 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 14: Junction to ambient thermal resistance for the 7 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.

Switch Saturation
Voltage

NPN Switch Current
Limit

Synchronization F
Threshold Voltage V
Synchronization V
Pin Current V
ON /OFF Pin (Pin 1) V
Threshold Voltage (Note 10)
ON /OFF Pin (Pin 1) V
Current V
Thermal Resistance T Package, Junction to Ambient 65

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

and

Figure 41

D

Figure 2

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

).

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

Figure 1

(Note 5) (Continued)

=

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

J

=

5V.

IN

=

I

SWITCH

5.0A 0.7 1.1/1.4 V

6.5 5.0 9.5 A

=

200 kHz 0.75 0.625/0.40 0.875/1.00 V

SYNC

=

COMP

=

5V 100 200 µA

IN

=

COMP

=

COMP

=

COMP

=

V

SH

=

1V, V

1V, V

IN

SYNC

5V

=

V

STH

1V 1.6 1.0/0.8 2.2/2.4 V

1V 40 15/10 65/75 µA

SHTH

(Note 11)
T Package, Junction to Ambient 45
(Note 12)
T Package, Junction to Case 2
S Package, Junction to Ambient 56 ˚C/W
(Note 13)
S Package, Junction to Ambient 35
(Note 14)
S Package, Junction to Ambient 26
(Note 15)
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

J(MAX)−TA(MAX)

]/θJA. When calculating the maximum

VOL

1

⁄2inch leads in a socket, or on a PC

1

⁄2inch leads soldered to a PC board

A(MAX)

.

≥ T

-

J

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All Output Voltage Versions
Electrical Characteristics

Note 15: Junction to ambient thermal resistance for the 7 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

®

software.

Simple

(Note 5) (Continued)

Typical Performance Characteristics

Supply Current
vs Temperature

Supply Current
vs Switch Current

Switch Saturation
Voltage vs Temperature

DS012420-2

DS012420-5

Reference Voltage
vs Temperature

Current Limit
vs Temperature

Switch Transconductance
vs Temperature

DS012420-3

DS012420-6

∆Reference Voltage
vs Supply Voltage

DS012420-4

Feedback Pin Bias
Current vs Temperature

DS012420-7

Oscillator Frequency
vs Temperature

DS012420-8

DS012420-9

DS012420-10

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Typical Performance Characteristics (Continued)

Error Amp Transconductance
vs Temperature

DS012420-11

Shutdown Supply Current
vs Temperature

DS012420-14

Connection Diagrams

Error Amp Voltage
Gain vs Temperature

ON /OFF Pin Current
vs Voltage

DS012420-12

DS012420-15

Short Circuit Frequency
vs Temperature

DS012420-13

Oscillator Frequency
vs Resistance

DS012420-16

Bent, Staggered Leads

7-Lead TO-220 (T)

Top View

DS012420-17

Order Number LM2588T-3.3, LM2588T-5.0,

LM2588T-12 or LM2588T-ADJ

See NS Package Number TA07B

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Bent, Staggered Leads

7-Lead TO-220 (T)

Side View

DS012420-18

Connection Diagrams (Continued)

Test Circuits

7-Lead TO-263 (S)

Top View

7-Lead TO-263 (S)

Side View

DS012420-20

DS012420-19

Order Number LM2588S-3.3, LM2588S-5.0,

LM2588S-12 or LM2588S-ADJ

Tape and Reel Order Number LM2588SX-3.3,

LM2588SX-5.0, LM2588SX-12 or LM2588SX-ADJ

See NS Package Number TS7B

C

— 100 µF, 25V Aluminum Electrolytic

IN1

C

— 0.1 µF Ceramic

IN2

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

— 680 µF, 16V Aluminum Electrolytic

OUT

CC— 0.47 µF Ceramic

—2k

R

C

DS012420-21

FIGURE 1. LM2588-3.3 and LM2588-5.0

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Test Circuits (Continued)

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: R1=Short (0Ω) and
R2=Open
For ADJ Devices: R1=48.75k,
R2=5.62k,±0.1

%

±

0.1%and

DS012420-22

FIGURE 2. LM2588-12 and LM2588-ADJ

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Block Diagram

For Fixed Versions

3.3V, R1=3.4k, R2=2k

5.0V, R1=6.15k, R2=2k
12V, R1=8.73k, R2=1k
For Adj. Version
R1=Short (0Ω), R2=Open

Flyback Regulator Operation

The LM2588 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-

DS012420-23

FIGURE 3.

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.

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Flyback Regulator Operation (Continued)

As shown in
regulator are shown in

Figure 4

, the LM2588 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, 10V/div
B: Switch Current, 5A/div
C: Output Rectifier Current, 5A/div
D: Output Ripple Voltage, 100 mV/div
AC-Coupled

FIGURE 5. Switching Waveforms

DS012420-60

FIGURE 6. V

DS012420-24

Figure 6

.

Response to Load Current Step

OUT

DS012420-61

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Typical Flyback Regulator Applications

Figure 7

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

through12show six typical flyback applications,

Figure

FIGURE 7. Single-Output Flyback Regulator

13

. For applications with different output
voltages— requiring the LM2588-ADJ —or different output
configurations that do not match the standard configurations,
refer to the

Switchers Made Simple

™

software.

DS012420-25

FIGURE 8. Single-Output Flyback Regulator

DS012420-26

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Typical Flyback Regulator Applications (Continued)

FIGURE 9. Single-Output Flyback Regulator

DS012420-27

FIGURE 10. Dual-Output Flyback Regulator

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DS012420-28

Typical Flyback Regulator Applications (Continued)

FIGURE 11. Dual-Output Flyback Regulator

DS012420-29

FIGURE 12. Triple-Output Flyback Regulator

DS012420-30

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Typical Flyback Regulator Applications (Continued)

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

Transformer

Type

Coilcraft Coilcraft (Note 16) Pulse (Note 17) Renco Schott

Manufacturers’ Part Numbers

(Note 16) Surface Mount Surface Mount (Note 18) (Note 19)
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 16: Coilcraft Inc.,: Phone: [phone]
1102 Silver Lake Road, Cary, IL 60013: Fax: [phone]
European Headquarters, 21 Napier Place: Phone: [phone]
Wardpark North, Cumbernauld, Scotland G68 0LL: Fax: [phone]
Note 17: Pulse Engineering Inc.,: Phone: [phone]
12220 World Trade Drive, San Diego, CA92128: Fax: [phone]
European Headquarters, Dunmore Road: Phone: [phone]
Tuam, Co. Galway, Ireland: Fax: [phone]
Note 18: Renco Electronics Inc.,: Phone: [phone]
60 Jeffryn Blvd. East, Deer Park, NY 11729: Fax: [phone]
Note 19: Schott Corp.,: Phone: [phone]
1000 Parkers Lane Road, Wayzata, MN 55391: Fax: [phone]

FIGURE 14. Transformer Manufacturer Guide

Transformer Footprints

Figure 15

through32show the footprints of each transformer, listed in

Figure 14

.

−12V

0.8

T1

DS012420-31

Top View

FIGURE 15. Coilcraft Q4434-B

www.national.com 16

T2

DS012420-32

Top View

FIGURE 16. Coilcraft Q4337-B

Typical Flyback Regulator
Applications

(Continued)

T3

T1

Top View

FIGURE 17. Coilcraft Q4343-B

T4

Top View

FIGURE 18. Coilcraft Q4344-B

T1

Top View

FIGURE 19. Coilcraft Q4435-B

(Surface Mount)

DS012420-33

DS012420-34

DS012420-35

DS012420-37

Top View

FIGURE 21. Pulse PE-68411

(Surface Mount)

T2

DS012420-38

Top View

FIGURE 22. Pulse PE-68412

(Surface Mount)

T3

DS012420-39

Top View

FIGURE 23. Pulse PE-68421

(Surface Mount)

T2

Top View

FIGURE 20. Coilcraft Q4436-B

(Surface Mount)

T4

DS012420-36

DS012420-40

Top View

FIGURE 24. Pulse PE-68422

(Surface Mount)

www.national.com17

Typical Flyback Regulator
Applications

(Continued)

T1

T4

Top View

FIGURE 25. Renco RL-5530

T2

Top View

FIGURE 26. Renco RL-5531

T3

Top View

FIGURE 27. Renco RL-5534

DS012420-41

DS012420-42

DS012420-43

DS012420-44

Top View

FIGURE 28. Renco RL-5535

T1

DS012420-45

Top View

FIGURE 29. Schott 67141450

T2

DS012420-46

Top View

FIGURE 30. Schott 67140860

T3

www.national.com 18

DS012420-47

Top View

FIGURE 31. Schott 67140920

Typical Flyback Regulator Applications (Continued)

T4

Top View

FIGURE 32. Schott 67140930

DS012420-48

www.national.com19

Step-Up (Boost) Regulator Operation

Figure 33

shows the LM2588 used as a step-up (boost)
regulator. This is a switching regulator that produces an out­put voltage greater than the input supply voltage.

A brief explanation of how the LM2588 Boost Regulator
works is as follows (refer to

Figure 33

). When the NPN
switch turns on, the inductor current ramps up at the rate of
V

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

IN

FIGURE 33. 12V Boost Regulator

By adding a smallnumber ofexternal components(as shownin
put voltage that is greater than the applied input voltage. The switching waveforms observed during the operation of this circuit
are shown in

Figure 34

. Typical performance of this regulator is shown in

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

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

DS012420-49

Figure 33

), the LM2588 canbe usedto producea regulatedout-

Figure 35

.

OUT

Typical Performance Characteristics

)

A: Switch Voltage,10V/div
B: Switch Current, 5A/div
C: Inductor Current, 5A/div
D: Output Ripple Voltage,
100 mV/div, AC-Coupled

DS012420-62

FIGURE 34. Switching Waveforms

www.national.com 20

FIGURE 35. V

Response to Load Current Step

OUT

DS012420-63

Typical Boost Regulator Applications

Figure 36

applications— one fixed and three using the adjustable ver­sion of the LM2588. Each drawing contains the part num­ber(s) and manufacturer(s) for every component. For the

Figure 37

of

Note 20: Coilcraft Inc.,: Phone: [phone]
1102 Silver Lake Road, Cary, IL 60013: Fax: [phone]
European Headquarters, 21 Napier Place: Phone: [phone]
Wardpark North, Cumbernauld, Scotland G68 0LL: Fax: [phone]
Note 21: Pulse Engineering Inc.,: Phone: [phone]
12220 World Trade Drive, San Diego, CA92128: Fax: [phone]
European Headquarters, Dunmore Road: Phone: [phone]
Tuam, Co. Galway, Ireland: Fax: [phone]
Note 22: Renco Electronics Inc.,: Phone: [phone]
60 Jeffryn Blvd. East, Deer Park, NY 11729: Fax: [phone]
Note 23: Schott Corp.,: Phone: [phone]
1000 Parkers Lane Road, Wayzata, MN 55391: Fax: [phone]

and38through40show four typical boost

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

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

Figure 36

.

Coilcraft (Note 20) Pulse (Note 21) Renco (Note 22) Schott (Note 23)

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

FIGURE 37. Inductor Selection Table

fixed 12V output application, the part numbersand manufac­turers’ names for the inductor are listed in a table in

37

. For applications with different output voltages, refer to

the

Switchers Made Simplesoftware.

Figure

DS012420-50

www.national.com21

Typical Boost Regulator Applications (Continued)

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

DS012420-51

DS012420-52

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

*

The LM2588 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.

DS012420-53

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

www.national.com 22

Application Hints

LM2588 SPECIAL FEATURES

DS012420-54

FIGURE 41. Shutdown Operation

SHUTDOWN CONTROL

A feature of the LM2588 is its ability to be shut down using
the ON /OFFpin (pin 1). This feature conservesinput power
by turning off thedevice when it is not inuse. For proper op­eration, an isolation diode is required (as shown in

41

).

The device will shut down when 3V or greater is applied on
the ON /OFF pin, sourcing current into pin 1. In shut down
mode, the device will draw typically 56 µA of supply current
(16 µA to V
vice back on, leave pin 1 floating, using an (isolation) diode,
as shown in

and 40 µA to the ON /OFF pin). Toturn the de-

IN

Figure 41

(for normal operation, do not source

or sink current to or from this pin— see the next section).

FREQUENCY ADJUSTMENT

The switching frequency of the LM2588 canbe adjusted with
the use of an external resistor.This featureallows the user to
optimize the size of the magnetics and the output capaci­tor(s) by tailoring the operating frequency. A resistor con­nected from pin 1 (the Freq. Adj. pin) to ground will set the
switching frequency from 100 kHz to 200 kHz (maximum).
As shown in

Figure 41

, the pin canbe usedto adjustthe fre­quency while still providing the shut down function.A curve in
the Performance Characteristics Section graphs the resistor
value to thecorresponding switching frequency.The table in

Figure 42

shows resistor values correspondingto commonly

used frequencies.
However, changing the LM2588’s operating frequency from

its nominal value of 100 kHz will change the magnetics se­lection and compensation component values.

R

(kΩ) Frequency (kHz)

SET

Open 100

200 125

47 150
33 175
22 200

FIGURE 42. Frequency Setting Resistor Guide

Figure

DS012420-55

FIGURE 43. Frequency Synchronization

FREQUENCY SYNCHRONIZATION

Another feature of the LM2588 is the ability to synchronize
the switching frequency to an external source, using the
sync pin (pin 6). This feature allows the user to parallel mul­tiple devices to deliver more output power.

A negative falling pulse applied to the sync pin will synchro­nize the LM2588 to an external oscillator (see

44

).

Figure 43

and

Use of this feature enables the LM2588 to be synchronized
to an external oscillator, such as a system clock. This opera­tion allows multiple power supplies to operate at the same
frequency, thus eliminating frequency-related noise
problems.

DS012420-64

FIGURE 44. Waveforms of a Synchronized

12V Boost Regulator

The scope photo in

Figure 44

shows a LM2588 12V Boost
Regulator synchronized to a 200 kHz signal. There is a 700
ns delay between the falling edgeof the sync signal and the
turning on of the switch.

PROGRAMMING OUTPUT VOLTAGE
(SELECTING R1 AND R2)

Referring to theadjustable regulator in

Figure 45

, the output
voltage is programmed by the resistors R1 and R2 bythe fol­lowing formula:

=

V

OUT

(1 + R1/R2) where V

V

REF

REF

=

1.23V

Resistors R1 and R2 divide the output voltage down so that
it can be compared with the 1.23V internal reference. With
R2 between 1k and 5k, R1 is:

R1=R2 (V

OUT/VREF

− 1) where V

REF

=

1.23V

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

Figure 45

), current flows directly from the
input, through the inductor and the diode, to the output, by­passing the switch. The current limit of the switch

does not

limit the output current for the entire circuit. To protect the

www.national.com23

Application Hints (Continued)

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 LM2588 will survive a short circuit to

Figure 46

), using the stan-

FIGURE 45. Boost Regulator

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.

DS012420-56

FIGURE 46. Flyback Regulator

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

Figure 46

and one for filtering (see

). Both are required due to
the inherent operation of a flyback regulator. To keep a
stable or constant voltage supply to the LM2588, 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 for the input

www.national.com 24

DS012420-57

capacitor. The storage capacitor will also attenuate noise
which may interfere with other circuits connected to the
same input supply voltage.

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.

and

IN

Application Hints (Continued)

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 typically 0.5V for Schottky diodes and 0.8V for

(Max):

IN

=

V

SW(OFF)

is the forward biased voltage of the output diode,

F

V

IN

(Max) + (V

ultra-fast recovery diodes. In certain circuits, there exists a
voltage spike, V
voltage (see

, superimposed on top of the steady-state

LL

Figure 5

, waveform A). 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, atran­sient suppressor in serieswith adiode isinserted acrossthe
transformer primary (as shown in the circuit in
other flyback regulator circuits throughout the datasheet).
The schematic in

Figure 46

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 5).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 LM2588 IC aswell. When usedin a flyback
regulator, the voltage at the Switch pin (pin 5) 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“ring­ing” 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 46

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, and the 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 5 and 4 (ground),
also shown in

Figure 46

. This prevents the voltage at pin 5
from dropping below −0.4V.The reversevoltage rating of the
diode must be greater than the switch off voltage.

, and the maximum in-

OUT

)/N

OUT+VF

Figure 4

and

. The values of the resistor

DS012420-58

FIGURE 47. 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:

V

≈ NxVINxD/(1−D)

OUT

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 LM2588 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 LM2588 if the input voltage has an unusually large
amount of transient noise, such as with an input switch that
bounces. The circuit in

Figure 47

demonstrates the layoutof
the filter, with the capacitor placed from the input pin to
ground and the resistor placed betweenthe input supplyand
the input pin. Note that the values of R
the schematic are good enough for most applications, but

and CINshown in

IN

some readjusting might be required for a particular applica­tion. If efficiency is amajor concern,replace theresistor with
a small inductor (say 10 µH and rated at 200 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

www.national.com25

Application Hints (Continued)

FIGURE 48. 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
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, a heat sink is not required to keep the
LM2588 junction temperature within the allowed operating
temperature range. For each application, to determine
whether or not a heat sink will be required, the following must
be identified:

1) Maximum ambient temperature (in the application).

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

3) Maximum allowed junction temperature (125˚C for the
LM2588). For a safe, conservative design, a temperature ap­proximately 15˚C cooler than the maximum junction tem­perature should be selected (110˚C).

4) LM2588 package thermal resistances θ
in the Electrical Characteristics).

Total power dissipated (P
as follows:

Boost:

VINis the minimum input voltage,V
N is the transformer turns ratio, D is the duty cycle, and I

Figure 48

). When using the Adjustable version,

and θJC(given

JA

) by the LM2588 can be estimated

D

is the output voltage,

OUT

LOAD

DS012420-59

is the maximum load current (and∑I
maximum load currents for multiple-output flyback regula-

is the sum of the

LOAD

tors). The duty cycle is given by:
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.

is the switch saturation voltage and can be

SAT

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

=

∆T

θJA.

P

•

J

D

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

=

T

J

∆T

J+TA

.

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:

=

∆T

(θJC+ θ

P

•

J

D

Interface

+ θ

Heat Sink

)

Again, the operating junction temperature will be:

=

∆T

T

J

J+TA

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

Included in the

Switchers Made Simple

design software is a
more precise (non-linear) thermal model that canbe 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.

www.national.com 26

Application Hints (Continued)

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 compatible computers from a
National Semiconductor sales office in your area or the Na­tional Semiconductor Customer Response Center

(1-800-272-9959).

www.national.com27

Physical Dimensions inches (millimeters) unless otherwise noted

Order Number LM2588T-3.3, LM2588T-5.0,

LM2588T-12 or LM2588T-ADJ

NS Package Number TA07B

www.national.com 28

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

Order Number LM2588S-3.3, LM2588S-5.0,

LM2588S-12 or LM2588S-ADJ

Tape and Reel Order Number LM2588SX-3.3,

LM2588SX-5.0, LM2588SX-12 or LM2588SX-ADJ

NS Package Number TS7B

LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
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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