LM2586T-12 [NSC]
SIMPLE SWITCHER 3A Flyback Regulator with Shutdown; SIMPLE SWITCHER 3A反激式稳压器，带有关断
| 型号： | LM2586T-12 |
| 厂家： | 
National Semiconductor |
| 描述： | SIMPLE SWITCHER 3A Flyback Regulator with Shutdown |
| 文件： | 总28页 (文件大小：780K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 1996
LM2586
SIMPLE SWITCHER® 3A Flyback Regulator with
Shutdown
General Description
Features
n Requires few external components
n Family of standard inductors and transformers
n NPN output switches 3.0A, can stand off 65V
n Wide input voltage range: 4V to 40V
The LM2586 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, and adjust-
able.
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
Requiring a minimum number of external components, these
regulators are cost effective, and simple to use. Included in
the datasheet are typical circuits of boost and flyback regula-
tors. Also listed are 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 3.0A 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 pro-
grammed up to 200 kHz. The oscillator can also be synchro-
nized with other devices, so that multiple devices can oper-
ate at the same switching frequency.
±
n System output voltage tolerance of 4% max over line
and load conditions
Typical Applications
n Flyback regulator
n Forward converter
n Multiple-output regulator
n Simple boost regulator
Other features include soft start mode to reduce in-rush cur-
rent 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 shut-
down pin, so that it can be turned off externally. An output
±
voltage tolerance of 4%, within specified input voltages and
output load conditions, is guaranteed for the power supply
system.
Flyback Regulator
DS012516-1
®
SIMPLE SWITCHER® and Switchers Made Simple are registered trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS012516
www.national.com
Ordering Information
Package Type
NSC Package
Drawing
TA07B
Order Number
7-Lead TO-220 Bent, Staggered Leads
7-Lead TO-263
LM2586T-3.3, LM2586T-5.0, LM2586T-12, LM2586T-ADJ
LM2586S-3.3, LM2586S-5.0, LM2586S-12, LM2586S-ADJ
TS7B
7-Lead TO-263 Tape and Reel
TS7B
LM2586SX-3.3, LM2586SX-5.0, LM2586SX-12,
LM2586SX-ADJ
www.national.com
2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Lead Temperature (Soldering, 10
sec.)
260˚C
150˚C
2 kV
Maximum Junction Temperature
(Note 3)
Minimum ESD Rating
=
=
(C 100 pF, R 1.5 kΩ)
Input Voltage
−0.4V ≤ VIN ≤ 45V
−0.4V ≤ VSW ≤ 65V
Internally Limited
Switch Voltage
Operating Ratings
Supply Voltage
Switch Current (Note 2)
Compensation Pin Voltage
Feedback Pin Voltage
ON /OFF Pin Voltage
Sync Pin Voltage
−0.4V ≤ VCOMP ≤ 2.4V
−0.4V ≤ VFB ≤ 2 VOUT
−0.4V ≤ VSH ≤ 6V
−0.4V ≤ VSYNC ≤ 2V
Internally Limited
4V ≤ VIN ≤ 40V
0V ≤ VSW ≤ 60V
ISW ≤ 3.0A
Output Switch Voltage
Output Switch Current
Junction Temp. Range
−40˚C ≤ TJ ≤ +125˚C
Power Dissipation (Note 3)
Storage Temperature Range
−65˚C to +150˚C
Electrical Characteristics
=
Specifications with standard type face are for TJ 25˚C, and those in bold type face apply over full Operating Temperature
=
Range. Unless otherwise specified, VIN 5V.
LM2586-3.3
Symbol
Parameters
Conditions
Typical
3.3
Min
Max
3.43/3.46
50/100
50/100
Units
V
SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4)
=
VOUT
Output Voltage
Line Regulation
Load Regulation
Efficiency
VIN 4V to 12V
3.17/3.14
=
ILOAD 0.3 to 1.2A
=
∆VOUT
/
/
VIN 4V to 12V
20
mV
mV
%
=
∆VIN
ILOAD 0.3A
=
∆VOUT
VIN 12V
20
=
ILOAD 0.3A to 1.2A
∆ILOAD
=
=
η
VIN 5V, ILOAD 0.3A
76
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
GM
Output Reference
Voltage
Measured at Feedback Pin
3.3
3.242/3.234
3.358/3.366
V
=
VCOMP 1.0V
=
Reference Voltage
Line Regulation
Error Amp
VIN 4V to 40V
2.0
mV
mmho
V/V
=
ICOMP −30 µA to +30 µA
1.193
260
0.678
2.259
=
VCOMP 1.0V
Transconductance
Error Amp
=
AVOL
VCOMP 0.5V to 1.6V
151/75
=
Voltage Gain
RCOMP 1.0 MΩ (Note 6)
LM2586-5.0
Symbol
Parameters
Conditions
Typical
5.0
Min
Max
5.20/5.25
50/100
50/100
Units
V
SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4)
=
VOUT
Output Voltage
Line Regulation
Load Regulation
Efficiency
VIN 4V to 12V
4.80/4.75
=
ILOAD 0.3A to 1.1A
=
∆VOUT
/
/
VIN 4V to 12V
20
mV
mV
%
=
∆VIN
ILOAD 0.3A
=
∆VOUT
VIN 12V
20
=
ILOAD 0.3A to 1.1A
∆ILOAD
=
=
η
VIN 12V, ILOAD 0.6A
80
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
Output Reference
Voltage
Measured at Feedback Pin
5.0
3.3
4.913/4.900
5.088/5.100
V
=
VCOMP 1.0V
=
∆VREF
Reference Voltage
VIN 4V to 40V
mV
3
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LM2586-5.0 (Continued)
Symbol
Parameters
Conditions
Typical
Min
Max
Units
UNIQUE DEVICE PARAMETERS (Note 5)
Line Regulation
=
GM
Error Amp
ICOMP −30 µA to +30 µA
0.750
165
0.447
1.491
mmho
V/V
=
VCOMP 1.0V
Transconductance
Error Amp
=
AVOL
VCOMP 0.5V to 1.6V
99/49
=
Voltage Gain
RCOMP 1.0 MΩ (Note 6)
LM2586-12
Symbol
Parameters
Conditions
Typical
12.0
20
Min
Max
Units
V
SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4)
=
VOUT
Output Voltage
Line Regulation
Load Regulation
Efficiency
VIN 4V to 10V
11.52/11.40
12.48/12.60
100/200
=
ILOAD 0.2A to 0.8A
=
∆VOUT
∆VIN
/
/
VIN 4V to 10V
mV
mV
%
=
ILOAD 0.2A
=
∆VOUT
VIN 10V
20
100/200
=
ILOAD 0.2A to 0.8A
∆ILOAD
=
=
η
VIN 10V, ILOAD 0.6A
93
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
GM
Output Reference
Voltage
Measured at Feedback Pin
12.0
7.8
11.79/11.76
12.21/12.24
V
=
VCOMP 1.0V
=
Reference Voltage
Line Regulation
Error Amp
VIN 4V to 40V
mV
mmho
V/V
=
ICOMP −30 µA to +30 µA
0.328
70
0.186
0.621
=
VCOMP 1.0V
Transconductance
Error Amp
=
AVOL
VCOMP 0.5V to 1.6V
41/21
=
Voltage Gain
RCOMP 1.0 MΩ (Note 6)
LM2586-ADJ
Symbol
Parameters
Conditions
Typical
Min
Max
Units
V
SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4)
=
VOUT
Output Voltage
Line Regulation
Load Regulation
Efficiency
VIN 4V to 10V
12.0
20
11.52/11.40
12.48/12.60
100/200
=
ILOAD 0.2A to 0.8A
=
∆VOUT
/
/
VIN 4V to 10V
mV
mV
%
=
∆VIN
ILOAD 0.2A
=
∆VOUT
VIN 10V
20
100/200
=
ILOAD 0.2A to 0.8A
∆ILOAD
=
=
η
VIN 10V, ILOAD 0.6A
93
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
GM
Output Reference
Voltage
Measured at Feedback Pin
1.230
1.5
1.208/1.205
1.252/1.255
V
=
VCOMP 1.0V
=
Reference Voltage
Line Regulation
Error Amp
VIN 4V to 40V
mV
mmho
=
ICOMP −30 µA to +30 µA
3.200
1.800
6.000
=
VCOMP 1.0V
Transconductance
Error Amp Voltage Gain
=
VCOMP 0.5V to 1.6V,
AVOL
IB
670
125
400/200
V/V
nA
=
RCOMP 1.0 MΩ (Note 6)
=
Error Amp
VCOMP 1.0V
425/600
Input Bias Current
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4
LM2586-ADJ (Continued)
Symbol
Parameters
Conditions
Typical
Min
Max
Units
COMMON DEVICE PARAMETERS for all versions (Note 5)
IS
Input Supply Current
Switch Off (Note 8)
11
50
16
15.5/16.5
100/115
100/300
mA
mA
µA
=
ISWITCH 1.8A
=
VSH 3V
IS/D
VUV
fO
Shutdown Input
Supply Current
=
Input Supply
RLOAD 100Ω
3.30
3.05
3.75
V
Undervoltage Lockout
Oscillator Frequency
Measured at Switch Pin
=
=
RLOAD 100Ω, VCOMP 1.0V
100
200
25
85/75
115/125
kHz
kHz
kHz
V
Freq. Adj. Pin Open (Pin 1)
=
RSET 22 kΩ
fSC
Short-Circuit
Frequency
Measured at Switch Pin
=
RLOAD 100Ω
=
VFEEDBACK 1.15V
VEAO
Error Amplifier
Output Swing
Upper Limit
(Note 7)
2.8
2.6/2.4
Lower Limit
(Note 8)
0.25
0.40/0.55
V
IEAO
Error Amp
(Note 9)
Output Current
(Source or Sink)
Soft Start Current
165
11.0
98
110/70
8.0/7.0
93/90
260/320
µA
µA
%
=
ISS
VFEEDBACK 0.92V
17.0/19.0
=
VCOMP 1.0V
=
DMAX
Maximum Duty Cycle
RLOAD 100Ω
(Note 7)
IL
Switch Leakage
Switch Off
15
300/600
µA
=
VSWITCH 60V
Current
=
VSUS
VSAT
ICL
Switch Sustaining Voltage
Switch Saturation Voltage
NPN Switch Current Limit
Synchronization
dV/dT 1.5V/ns
65
V
V
A
V
=
ISWITCH 3.0A
0.45
4.0
0.65/0.9
7.0
3.0
=
VSTH
FSYNC 200 kHz
0.75
0.625/0.40
0.875/1.00
= =
VCOMP 1V, VIN 5V
Threshold Voltage
Synchronization
=
ISYNC
VSHTH
ISH
VIN 5V
100
1.6
40
200
µA
V
= =
VCOMP 1V, VSYNC VSTH
Pin Current
=
ON/OFF Pin (Pin 1)
Threshold Voltage
ON/OFF Pin (Pin 1)
Current
VCOMP 1V
1.0/0.8
15/10
2.2/2.4
65/75
(Note 10)
=
VCOMP 1V
µA
=
VSH VSHTH
θJA
θJA
Thermal Resistance
T Package, Junction to
Ambient (Note 11)
65
45
T Package, Junction to
Ambient (Note 12)
θJC
θJA
T Package, Junction to Case
2
S Package, Junction to
Ambient (Note 13)
56
˚C/W
θJA
θJA
θJC
S Package, Junction to
Ambient (Note 14)
35
26
2
S Package, Junction to
Ambient (Note 15)
S Package, Junction to Case
5
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LM2586-ADJ (Continued)
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 indicate conditions for which the device is intended to be functional, but device parameter specifications may not be guar-
anteed 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 LM2586 is used as
a step-up regulator. To prevent damage to the switch, the output current must be externally limited to 3A. However, output current is internally limited when the
LM2586 is used as a flyback regulator (see the Application Hints section for more information).
Note 3: The junction temperature of the device (T ) is a function of the ambient temperature (T ), the junction-to-ambient thermal resistance (θ ), and the power
JA
J
A
dissipation of the device (P ). A thermal shutdown will occur if the temperature exceeds the maximum junction temperature of the device: P x θ + T
JA A(MAX)
≥ T -
J
D
D
(MAX). For a safe thermal design, check that the maximum power dissipated by the device is less than: P ≤ [T
− T ]/θ . When calculating the maximum
A(MAX) JA
D
J(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 LM2586 is used as
shown in Figures 1, 2, system performance will be as specified by the system parameters.
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 measuring A
.
VOL
Note 7: To measure 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: To measure 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: To measure the worst-case error amplifier output current, the LM2586 is tested with the feedback voltage set to its low value (Note 7) and at its high value
(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 Figure 41).
Note 11: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1
⁄
2
inch leads in a socket, or on a PC
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 1⁄2 inch leads soldered to a PC board
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 lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches (3.6 times the area
of the TO-263 package) of 1 oz. (0.0014 in. thick) copper.
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 Simple® software.
Typical Performance Characteristics
Supply Current
vs Temperature
Reference Voltage
vs Temperature
∆Reference Voltage
vs Supply Voltage
DS012516-2
DS012516-3
DS012516-4
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6
Typical Performance Characteristics (Continued)
Supply Current
Current Limit
Feedback Pin Bias
vs Switch Current
vs Temperature
Current vs Temperature
DS012516-5
DS012516-6
DS012516-9
DS012516-12
DS012516-7
DS012516-10
DS012516-13
Switch Saturation
Voltage vs Temperature
Switch Transconductance
vs Temperature
Oscillator Frequency
vs Temperature
DS012516-8
Error Amp Transconductance
vs Temperature
Error Amp Voltage
Gain vs Temperature
Short Circuit Frequency
vs Temperature
DS012516-11
7
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Typical Performance Characteristics (Continued)
Shutdown Supply Current
vs Temperature
ON/OFF Pin Current
vs Voltage
Oscillator Frequency
vs Resistance
DS012516-14
DS012516-15
DS012516-16
Connection Diagrams
Bent, Staggered Leads
7-Lead TO-220 (T)
Top View
Bent, Staggered Leads
7-Lead TO-220 (T)
Side View
DS012516-18
DS012516-17
Order Number LM2586T3.3, LM2586T-5.0,
LM2586T-12 or LM2586T-ADJ
See NS Package Number TA07B
7-Lead TO-263 (S)
Top View
7-Lead TO-263 (S)
Side View
DS012516-20
DS012516-19
Order number LM2586S-3.3, LM2586S-5.0,
LM2586S-12 or LM2586S-ADJ
Tape and Reel Order Number LM2586SX-3.3,
LM2586SX-5.0, LM2586SX-12 or LM2586SX-ADJ
See NS Package Number TS7B
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8
Test Circuits
DS012516-21
C
C
— 100 µF, 25V Aluminum Electrolytic
— 0.1 µF Ceramic
IN1
IN2
T — 22 µH, 1:1 Schott #67141450
D — 1N5820
C
C
R
— 680 µF, 16V Aluminum Electrolytic
— 0.47 µF Ceramic
— 2k
OUT
C
C
FIGURE 1. LM2586-3.3 and LM2586-5.0
DS012516-22
C
C
— 100 µF, 25V Aluminum Electrolytic
— 0.1 µF Ceramic
IN1
IN2
L — 15 µH, Renco #RL-5472-5
D — 1N5820
C
C
R
— 680 µF, 16V Aluminum Electrolytic
— 0.47 µF Ceramic
— 2k
OUT
C
C
=
=
For 12V Devices: R1 Short (0Ω) and 2 Open
=
=
±
±
For ADJ Devices: R1 48.75k, 0.1% and 2 5.62k, 0.1%
FIGURE 2. LM2586-12 and LM2586-ADJ
9
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Block Diagram
DS012516-23
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
FIGURE 3.
Flyback Regulator Operation
The LM2586 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 Figure 4, or multiple out-
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.
lapses, reversing the voltage polarity of the primary and sec-
ondary 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 differ-
ence between the feedback voltage and a 1.230V reference.
The error amp output voltage is compared to a ramp voltage
proportional to the switch current (i.e., inductor current dur-
ing 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.
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 pri-
mary. When the switch turns off, the magnetic field col-
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10
Flyback Regulator Operation (Continued)
DS012516-24
As shown in Figure 4, the LM2586 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this
regulator are shown in Figure 5. Typical Performance Characteristics observed during the operation of this circuit are shown in Figure 6.
FIGURE 4. 12V Flyback Regulator Design Example
Typical Performance Characteristics
DS012516-65
A: Switch Voltage, 20V/div
B: Switch Current, 2A/div
C: Output Rectifier Current, 2A/div
D: Output Ripple Voltage, 50 mV/div AC-Coupled
FIGURE 5. Switching Waveforms
11
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Typical Performance Characteristics (Continued)
DS012516-66
FIGURE 6. VOUT Response to Load Current Step
Typical Flyback Regulator Applications
Figure 7 through Figure 12 show six typical flyback applica-
tions, varying from single output to triple output. Each draw-
ing contains the part number(s) and manufacturer(s) for ev-
ery 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 LM2586-ADJ — or different output
configurations that do not match the standard configurations,
refer to the Switchers Made Simple software.
DS012516-27
FIGURE 7. Single-Output Flyback Regulator
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12
Typical Flyback Regulator Applications (Continued)
DS012516-28
FIGURE 8. Single-Output Flyback Regulator
DS012516-29
FIGURE 9. Single-Output Flyback Regulator
13
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Typical Flyback Regulator Applications (Continued)
DS012516-30
FIGURE 10. Dual-Output Flyback Regulator
DS012516-31
FIGURE 11. Dual-Output Flyback Regulator
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14
Typical Flyback Regulator Applications (Continued)
DS012516-32
FIGURE 12. Triple-Output Flyback Regulator
Transformer Selection (T)
Figure 13 lists the standard transformers available for flyback regulator applications. Included in the table are the turns ratio(s) for
each transformer, as well as the output voltages, input voltage ranges, and the maximum load currents for each circuit.
Applications
Transformers
VIN
Figure 7
T7
Figure 8
T7
Figure 9
T7
Figure 10
T6
Figure 11
T6
Figure 12
T5
4V–6V
3.3V
1.4A
1
4V–6V
5V
8V–16V
12V
4V–6V
12V
18V–36V
12V
18V–36V
5V
VOUT1
IOUT1 (Max)
N1
1A
0.8A
1
0.15A
1.2
0.6A
1.8A
1
1.2
0.5
VOUT2
−12V
0.15A
1.2
−12V
0.6A
12V
I
OUT2(Max)
0.25A
1.15
N2
1.2
VOUT3
IOUT3 (Max)
N3
−12V
0.25A
1.15
FIGURE 13. Transformer Selection Table
15
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Typical Flyback Regulator Applications (Continued)
Transformer
Type
Manufacturers’ Part Numbers
Coilcraft (Note
16) Surface
Mount
Pulse (Note 17)
Coilcraft
Pulse (Note
Renco (Note Schott (Note
Surface Mount
(Note 16)
17)
18)
19)
T5
T6
T7
Q4338-B
Q4437-B
PE-68413
PE-68414
—
—
—
RL-5532
RL-5533
RL-5751
67140890
67140900
26606
Q4339-B
S6000-A
Q4438-B
S6057-A
PE-68482
Note 16: Coilcraft Inc., Phone: (800) 322-2645
1102 Silver Lake Road, Cary, IL 60013 Fax: (708) 639-1469
European Headquarters, 21 Napier Place Phone: +44 1236 730 595
Wardpark North, Cumbernauld, Scotland G68 0LL Fax: +44 1236 730 627
Note 17: Pulse Engineering Inc., Phone: (619) 674-8100
12220 World Trade Drive, San Diego, CA 92128 Fax: (619) 674-8262
European Headquarters, Dunmore Road Phone: +353 93 24 107
Tuam, Co. Galway, Ireland Fax: +353 93 24 459
Note 18: Renco Electronics Inc., Phone: (800) 645-5828
60 Jeffryn Blvd. East, Deer Park, NY 11729 Fax: (516) 586-5562
Note 19: Schott Corp., Phone: (612) 475-1173
1000 Parkers Lane Road, Wayzata, MN 55391 Fax: (612) 475-1786
FIGURE 14. Transformer Manufacturer Guide
Transformer Footprints
Figure 15 through Figure 29 show the footprints of each transformer, listed in Figure 14.
T7
T5
DS012516-33
Top View
FIGURE 15. Coilcraft S6000-A
DS012516-35
T6
FIGURE 17. Coilcraft Q4437-B (Surface Mount)
T5
DS012516-34
Top View
FIGURE 16. Coilcraft Q4339-B
DS012516-36
Top View
FIGURE 18. Coilcraft Q4338-B
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16
Typical Flyback Regulator
Applications (Continued)
T5
T7
DS012516-42
DS012516-37
Top View
Top View
FIGURE 23. Pulse PE-68413
(Surface Mount)
FIGURE 19. Coilcraft S6057-A
(Surface Mount)
T7
T6
DS012516-43
Top View
FIGURE 24. Renco RL-5751
DS012516-38
Top View
FIGURE 20. Coilcraft Q4438-B
(Surface Mount)
T6
T7
DS012516-45
Top View
DS012516-39
FIGURE 25. Renco RL-5533
Top View
FIGURE 21. Pulse PE-68482
T5
T6
DS012516-46
DS012516-40
Top View
FIGURE 26. Renco RL-5532
Top View
FIGURE 22. Pulse PE-68414
(Surface Mount)
17
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Typical Flyback Regulator Applications (Continued)
T7
DS012516-47
Top View
FIGURE 27. Schott 26606
T6
T5
DS012516-49
Top View
FIGURE 28. Schott 67140900
DS012516-50
Top View
FIGURE 29. Schott 67140890
Step-Up (Boost) Regulator Operation
Figure 30 shows the LM2586 used as a step-up (boost)
regulator. This is a switching regulator that produces an out-
put voltage greater than the input supply voltage.
off, the lower end of the inductor flies above VIN, discharging
its current through diode (D) into the output capacitor (COUT
)
at a rate of (VOUT − VIN)/L. Thus, energy stored in the induc-
tor during the switch on time is transferred to the output dur-
ing the switch off time. The output voltage is controlled by
adjusting the peak switch current, as described in the flyback
regulator section.
A brief explanation of how the LM2586 Boost Regulator
works is as follows (refer to Figure 30). When the NPN
switch turns on, the inductor current ramps up at the rate of
V
IN/L, storing energy in the inductor. When the switch turns
DS012516-51
FIGURE 30. 12V Boost Regulator
By adding a small number of external components (as shown in Figure 30), the LM2586 can be used to produce a regulated out-
put voltage that is greater than the applied input voltage. The switching waveforms observed during the operation of this circuit
are shown in Figure 31. Typical performance of this regulator is shown in Figure 32.
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Typical Performance Characteristics
DS012516-67
A: Switch Voltage,10V/div
B: Switch Current, 2A/div
C: Inductor Current, 2A/div
D: Output Ripple Voltage,100 mV/div, AC-Coupled
FIGURE 31. Switching Waveforms
DS012516-68
FIGURE 32. VOUT Response to Load Current Step
Typical Boost Regulator Applications
Figures 33, 35 through Figure 37 show four typical boost
applications — one fixed and three using the adjustable ver-
sion of the LM2586. Each drawing contains the part num-
ber(s) and manufacturer(s) for every component. For the
fixed 12V output application, the part numbers and manufac-
turers’ names for the inductor are listed in a table in Figure
34. For applications with different output voltages, refer to
the Switchers Made Simple software.
DS012516-54
FIGURE 33. +5V to +12V Boost Regulator
19
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Typical Boost Regulator Applications (Continued)
Figure 34 contains a table of standard inductors, by part number and corresponding manufacturer, for the fixed output regulator
of Figure 33.
Schott
Coilcraft
Pulse
Renco
Schott
(Note 23)
(Surface Mount)
67146540
(Note 20)
(Note 21)
(Note 22)
(Note 23)
DO3316-153
PE-53898
RL-5471-7
67146510
Note 20: Coilcraft Inc., Phone: (800) 322-2645
1102 Silver Lake Road, Cary, IL 60013 Fax: (708) 639-1469
European Headquarters, 21 Napier Place Phone: +44 1236 730 595
Wardpark North, Cumbernauld, Scotland G68 0LL Fax: +44 1236 730 627
Note 21: Pulse Engineering Inc., Phone: (619) 674-8100
12220 World Trade Drive, San Diego, CA 92128 Fax: (619) 674-8262
European Headquarters, Dunmore Road Phone: +353 93 24 107
Tuam, Co. Galway, Ireland Fax: +353 93 24 459
Note 22: Renco Electronics Inc., Phone: (800) 645-5828
60 Jeffryn Blvd. East, Deer Park, NY 11729 Fax: (516) 586-5562
Note 23: Schott Corp., Phone: (612) 475-1173
1000 Parkers Lane Road, Wayzata, MN 55391 Fax: (612) 475-1786
FIGURE 34. Inductor Selection Table
DS012516-55
FIGURE 35. +12V to +24V Boost Regulator
DS012516-56
FIGURE 36. +24V to +36V Boost Regulator
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20
Typical Boost Regulator Applications (Continued)
DS012516-57
FIGURE 37. +24V to +48V Boost Regulator
Note 24: The LM2586 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.
Application Hints
LM2586 SPECIAL FEATURES
DS012516-58
FIGURE 38. Shutdown Operation
SHUTDOWN CONTROL
switching frequency from 100 kHz to 200 kHz (maximum).
As shown in Figure 38, the pin can be used to adjust the fre-
quency while still providing the shut down function. A curve in
the Performance Characteristics Section graphs the resistor
value to the corresponding switching frequency. The table in
Figure 39 shows resistor values corresponding to commonly
used frequencies.
A feature of the LM2586 is its ability to be shut down using
the ON /OFF pin (pin 1). This feature conserves input power
by turning off the device when it is not in use. For proper op-
eration, an isolation diode is required (as shown in Figure
38).
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 VIN and 40 µA to the ON /OFF pin). To turn the de-
vice back on, leave pin 1 floating, using an (isolation) diode,
as shown in Figure 38 (for normal operation, do not source
or sink current to or from this pin — see the next section).
However, changing the LM2586’s operating frequency from
its nominal value of 100 kHz will change the magnetics se-
lection and compensation component values.
RSET(kΩ)
Open
200
Frequency (kHz)
100
125
150
175
200
FREQUENCY ADJUSTMENT
The switching frequency of the LM2586 can be adjusted with
the use of an external resistor. This feature allows the user to
optimize the size of the magnetics and the output capaci-
tor(s) by tailoring the operating frequency. A resistor con-
nected from pin 1 (the Freq. Adj. pin) to ground will set the
47
33
22
FIGURE 39. Frequency Setting Resistor Guide
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21
tion allows multiple power supplies to operate at the same
frequency, thus eliminating frequency-related noise
problems.
Application Hints (Continued)
DS012516-59
FIGURE 40. Frequency Synchronization
FREQUENCY SYNCHRONIZATION
Another feature of the LM2586 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 mul-
tiple devices to deliver more output power.
A negative falling pulse applied to the sync pin will synchro-
nize the LM2586 to an external oscillator (see Figures 40,
41).
DS012516-69
FIGURE 41. Waveforms of a Synchronized
12V Boost Regulator
Use of this feature enables the LM2586 to be synchronized
to an external oscillator, such as a system clock. This opera-
The scope photo in Figure 41 shows a LM2586 12V Boost
Regulator synchronized to a 200 kHz signal. There is a 700
ns delay between the falling edge of the sync signal and the
turning on of the switch.
DS012516-61
FIGURE 42. Boost Regulator
PROGRAMMING OUTPUT VOLTAGE
(SELECTING R1 AND R2)
externally limited, either by the input supply or at the output
with an external current limit circuit. The external limit should
be set to the maximum switch current of the device, which is
3A.
Referring to the adjustable regulator in Figure 42, the output
voltage is programmed by the resistors R1 and R2 by the fol-
lowing formula:
In a flyback regulator application (Figure 43), using the stan-
dard transformers, the LM2586 will survive a short circuit to
the main output. When the output voltage drops to 80% 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 be-
fore the switch turns back on. Hence, the switch turns on ini-
tially with zero current at its collector. In this condition, the
switch current limit will limit the peak current, saving the de-
vice.
=
=
where VREF 1.23V
VOUT VREF (1 + R1/R2)
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:
=
=
where VREF 1.23V
R1 R2 (VOUT/VREF − 1)
For best temperature coefficient and stability with time, use
1% metal film resistors.
SHORT CIRCUIT CONDITION
FLYBACK REGULATOR INPUT CAPACITORS
Due to the inherent nature of boost regulators, when the out-
put is shorted (see Figure 42), current flows directly from the
input, through the inductor and the diode, to the output, by-
passing the switch. The current limit of the switch does not
limit the output current for the entire circuit. To protect the
load and prevent damage to the switch, the current must be
A flyback regulator draws discontinuous pulses of current
from the input supply. Therefore, there are two input capaci-
tors needed in a flyback regulator — one for energy storage
and one for filtering (see Figure 43). Both are required due to
the inherent operation of a flyback regulator. To keep a
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22
might be very large. This means a larger value of capaci-
tance or a higher voltage rating will be needed for the input
capacitor. The storage capacitor will also attenuate noise
which may interfere with other circuits connected to the
same input supply voltage.
Application Hints (Continued)
stable or constant voltage supply to the LM2586, a storage
capacitor (≥100 µF) is required. If the input source is a recti-
fied DC supply and/or the application has a wide tempera-
ture range, the required rms current rating of the capacitor
DS012516-62
FIGURE 43. Flyback Regulator
In addition, a small bypass capacitor is required due to the
noise generated by the input current pulses. To eliminate the
noise, insert a 1.0 µF ceramic capacitor between VIN and
ground as close as possible to the device.
regulator, the voltage at the Switch pin (pin 5) can go nega-
tive when the switch turns on. The “ringing” voltage at the
switch pin is caused by the output diode capacitance and the
transformer leakage inductance forming a resonant circuit at
the secondary(ies). The resonant circuit generates the “ring-
ing” voltage, which gets reflected back through the trans-
former to the switch pin. There are two common methods to
avoid this problem. One is to add an RC snubber around the
output rectifier(s), as in Figure 43. 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 between 10Ω and 1 kΩ, and the capacitor will
vary from 0.001 µF to 0.1 µF. Adding a snubber will (slightly)
reduce the efficiency of the overall circuit.
SWITCH VOLTAGE LIMITS
In a flyback regulator, the maximum steady-state voltage ap-
pearing at the switch, when it is off, is set by the transformer
turns ratio, N, the output voltage, VOUT, and the maximum in-
put voltage, VIN (Max):
=
VSW(OFF) VIN (Max) + (VOUT +VF)/N
where VF is the forward biased voltage of the output diode,
and is typically 0.5V for Schottky diodes and 0.8V for
ultra-fast recovery diodes. In certain circuits, there exists a
voltage spike, VLL, superimposed on top of the steady-state
voltage (see 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 volt-
age at the switch from exceeding its maximum value, a tran-
sient suppressor in series with a diode is inserted across the
transformer primary (as shown in the circuit in Figure 4 and
other flyback regulator circuits throughout the datasheet).
The schematic in Figure 43 shows another method of clamp-
ing 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 volt-
age across the primary.
The other method to reduce or eliminate the “ringing” is to in-
sert a Schottky diode clamp between pins 5 and 4 (ground),
also shown in Figure 43. This prevents the voltage at pin 5
from dropping below −0.4V. The reverse voltage rating of the
diode must be greater than the switch off voltage.
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 LM2586 IC as well. When used in a flyback
23
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OUTPUT VOLTAGE LIMITATIONS
Application Hints (Continued)
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:
VOUT ≈ N x VIN x D/(1 − D)
The duty cycle of a flyback regulator is determined by the fol-
lowing equation:
Theoretically, the maximum output voltage can be as large
as desired — just keep increasing the turns ratio of the trans-
former. However, there exists some physical limitations that
prevent the turns ratio, and thus the output voltage, from in-
creasing to infinity. The physical limitations are capacitances
and inductances in the LM2586 switch, the output diode(s),
and the transformer — such as reverse recovery time of the
output diode (mentioned above).
DS012516-63
FIGURE 44. Input Line Filter
NOISY INPUT LINE CONDITION
A small, low-pass RC filter should be used at the input pin of
the LM2586 if the input voltage has an unusually large
amount of transient noise, such as with an input switch that
bounces. The circuit in Figure 44 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 RIN and CIN shown in
the schematic are good enough for most applications, but
some readjusting might be required for a particular applica-
tion. If efficiency is a major concern, replace the resistor with
a small inductor (say 10 µH and rated at 200 mA).
STABILITY
All current-mode controlled regulators can suffer from an in-
stability, known as subharmonic oscillation, if they operate
with a duty cycle above 50%. To eliminate subharmonic os-
cillations, a minimum value of inductance is required to en-
sure stability for all boost and flyback regulators. The mini-
mum inductance is given by:
where VSAT is the switch saturation voltage and can be
found in the Characteristic Curves.
DS012516-64
FIGURE 45. Circuit Board Layout
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24
Application Hints (Continued)
CIRCUIT LAYOUT GUIDELINES
As in any switching regulator, layout is very important. Rap-
idly switching currents associated with wiring inductance
generate voltage transients which can cause problems. For
minimal inductance and ground loops, keep the length 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 in-
dicated in Figure 45). When using the Adjustable version,
physically locate the programming resistors as near the
regulator IC as possible, to keep the sensitive feedback wir-
ing short.
where VF is the forward biased voltage of the diode and is
typically 0.5V for Schottky diodes and 0.8V for fast recovery
diodes. VSAT is the switch saturation voltage and can be
found in the Characteristic Curves.
When no heat sink is used, the junction temperature rise is:
=
∆TJ PD • θJA
.
Adding the junction temperature rise to the maximum ambi-
ent temperature gives the actual operating junction tempera-
ture:
HEAT SINK/THERMAL CONSIDERATIONS
In many cases, a heat sink is not required to keep the
LM2586 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:
=
TJ ∆TJ + TA.
If the operating junction temperature exceeds the maximum
junction temperatue in item 3 above, then a heat sink is re-
quired. When using a heat sink, the junction temperature rise
can be determined by the following:
1) Maximum ambient temperature (in the application).
2) Maximum regulator power dissipation (in the application).
=
∆TJ PD • (θJC + θInterface + θHeat Sink
)
3) Maximum allowed junction temperature (125˚C for the
LM2586). For a safe, conservative design, a temperature ap-
proximately 15˚C cooler than the maximum junction tem-
perature should be selected (110˚C).
Again, the operating junction temperature will be:
=
TJ ∆TJ + TA
As before, if the maximum junction temperature is exceeded,
a larger heat sink is required (one that has a lower thermal
resistance).
4) LM2586 package thermal resistances θJA and θJC (given
in the Electrical Characteristics).
Total power dissipated (PD) by the LM2586 can be estimated
as follows:
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 calcu-
late the heat sink thermal resistance required to maintain the
regulator junction temperature below the maximum operat-
ing temperature.
To further simplify the flyback regulator design procedure,
National Semiconductor is making available computer de-
sign software to be used with the Simple Switcher® line of
switching regulators. Switchers Made Simple is available
on a 31⁄
tional Semiconductor sales office in your area or the National
2
" diskette for IBM compatible computers from a Na-
VIN is the minimum input voltage, VOUT is the output voltage,
N is the transformer turns ratio, D is the duty cycle, and ILOAD
Semiconductor
Customer
Response
Center
(1-800-272-9959).
∑
is the maximum load current (and ILOAD is the sum of the
maximum load currents for multiple-output flyback regula-
tors). The duty cycle is given by:
25
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26
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM2586T-3.3, LM2586T-5.0,
LM2586T-12 or LM2586T-ADJ
NS Package Number TA07B
27
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Order Number LM2586S-3.3, LM2586S-5.0,
LM2586S-12 or LM2586S-ADJ
Tape and Reel Order Number LM2586SX-3.3,
LM2586SX-5.0, LM2586SX-12 or LM2586SX-ADJ
NS Package Number TS7B
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1. Life support devices or systems are devices or sys-
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ure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be rea-
sonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
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Tel: 1-800-272-9959
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