NSC LM2588T-3.3 Simple switcherâ® 5a flyback regulator with shutdown Datasheet

LM2588
SIMPLE SWITCHER ® 5A Flyback Regulator with
Shutdown
General Description
Features
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, and adjustable.
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 regulators. 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 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 200 kHz. The oscillator can also be synchronized with other devices, so that multiple devices can operate at the same switching frequency.
Other features include soft 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 ± 4%, within specified input voltages and output load conditions, is guaranteed for the power
supply system.
Requires few external components
Family of standard inductors and transformers
NPN output switches 5.0A, can stand off 65V
Wide input voltage range: 4V to 40V
Adjustable switching frequency: 100 kHz to 200 kHz
External shutdown capability
Draws less than 60 µA when shut down
Frequency synchronization
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 ± 4% max over line
and load conditions
n
n
n
n
n
n
n
n
n
Typical Applications
n
n
n
n
Flyback regulator
Forward converter
Multiple-output regulator
Simple boost regulator
Connection Diagrams
Bent, Staggered Leads
7-Lead TO-220 (T)
Top View
Bent, Staggered Leads
7-Lead TO-220 (T)
Side View
01242018
01242017
Order Number LM2588T-3.3, LM2588T-5.0,
LM2588T-12 or LM2588T-ADJ
See NS Package Number TA07B
SIMPLE SWITCHER ® and Switchers Made Simple
®
© 2005 National Semiconductor Corporation
are registered trademarks of National Semiconductor Corporation.
DS012420
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LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown
July 2005
LM2588
Connection Diagrams
(Continued)
7-Lead TO-263 (S)
Top View
7-Lead TO-263 (S)
Side View
01242020
01242019
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
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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2
Lead Temperature
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Junction Temperature
(Soldering, 10 sec.)
(Note 3)
−0.4V ≤ VIN ≤ 45V
Input Voltage
Internally Limited
Compensation Pin Voltage
−0.4V ≤ VCOMP ≤
2.4V
150˚C
Minimum ESD Rating
−0.4V ≤ VSW ≤ 65V
Switch Voltage
Switch Current (Note 2)
260˚C
(C = 100 pF, R = 1.5 kΩ)
2 kV
Operating Ratings
4V ≤ VIN ≤ 40V
Supply Voltage
Feedback Pin Voltage
−0.4V ≤ VFB ≤ 2
VOUT
Output Switch Voltage
0V ≤ VSW ≤ 60V
ON /OFF Pin Voltage
−0.4V ≤ VSH ≤ 6V
Output Switch Current
ISW ≤ 5.0A
−0.4V ≤ VSYNC ≤ 2V
Junction Temperature
Range
−40˚C ≤ TJ ≤ +125˚C
Sync Pin Voltage
Power Dissipation (Note 3)
Internally Limited
Storage Temperature Range
−65˚C to +150˚C
LM2588-3.3 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.
Symbol
Parameters
Conditions
Typical
Min
Max
Units
3.3
3.17/3.14
3.43/3.46
V
20
50/100
mV
20
50/100
mV
SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4)
VOUT
Output Voltage
VIN = 4V to 12V
ILOAD = 400 mA to 1.75A
∆VOUT/
Line Regulation
VIN = 4V to 12V
Load Regulation
VIN = 12V
∆VIN
∆VOUT/
ILOAD = 400 mA
∆ILOAD
η
ILOAD = 400 mA to 1.75A
Efficiency
VIN = 12V, ILOAD = 1A
75
%
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
Output Reference
Measured at Feedback Pin
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
3.3
3.242/3.234
3.358/3.366
2.0
V
mV
Line Regulation
GM
AVOL
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ (Note 6)
1.193
0.678
260
151/75
2.259
mmho
V/V
LM2588-5.0 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.
Symbol
Parameters
Conditions
Typical
Min
Max
Units
5.0
4.80/4.75
5.20/5.25
V
20
50/100
mV
20
50/100
mV
SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4)
VOUT
Output Voltage
∆VOUT/
Line Regulation
VIN = 4V to 12V
ILOAD = 500 mA to 1.45A
∆VIN
∆VOUT/
ILOAD = 500 mA
Load Regulation
VIN = 12V
Efficiency
VIN = 12V, ILOAD = 750 mA
∆ILOAD
η
VIN = 4V to 12V
ILOAD = 500 mA to 1.45A
80
%
UNIQUE DEVICE PARAMETERS (Note 5)
3
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LM2588
Absolute Maximum Ratings (Note 1)
LM2588
LM2588-5.0 Electrical Characteristics
(Continued)
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.
Symbol
VREF
∆VREF
Parameters
Output Reference
Conditions
Measured at Feedback Pin
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
Typical
Min
Max
Units
5.0
4.913/4.900
5.088/5.100
V
3.3
mV
Line Regulation
GM
AVOL
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ (Note 6)
0.750
0.447
165
99/49
1.491
mmho
V/V
LM2588-12 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.
Symbol
Parameters
Conditions
Typical
Min
Max
Units
12.0
11.52/11.40
12.48/12.60
V
20
100/200
mV
20
100/200
mV
SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4)
VOUT
Output Voltage
VIN = 4V to 10V
ILOAD = 300 mA to 1.2A
∆VOUT/
Line Regulation
VIN = 4V to 10V
Load Regulation
VIN = 10V
∆VIN
∆VOUT/
ILOAD = 300 mA
∆ILOAD
η
ILOAD = 300 mA to 1.2A
Efficiency
VIN = 10V, ILOAD = 1A
90
%
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
Output Reference
Measured at Feedback Pin
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
12.0
11.79/11.76
12.21/12.24
7.8
V
mV
Line Regulation
GM
AVOL
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ (Note 6)
0.328
0.186
70
41/21
0.621
mmho
V/V
LM2588-ADJ 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.
Symbol
Parameters
Conditions
Typical
Min
Max
Units
12.0
11.52/11.40
12.48/12.60
V
20
100/200
mV
20
100/200
mV
SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4)
VOUT
Output Voltage
VIN = 4V to 10V
ILOAD = 300 mA to 1.2A
∆VOUT/
Line Regulation
∆VIN
∆VOUT/
ILOAD = 300 mA
Load Regulation
VIN = 10V
Efficiency
VIN = 10V, ILOAD = 1A
∆ILOAD
η
VIN = 4V to 10V
ILOAD = 300 mA to 1.2A
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90
4
%
(Continued)
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.
Symbol
Parameters
Conditions
Typical
Min
Max
Units
1.230
1.208/1.205
1.252/1.255
V
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
Output Reference
Measured at Feedback Pin
Voltage
VCOMP = 1.0V
Reference Voltage
VIN = 4V to 40V
1.5
mV
Line Regulation
GM
AVOL
IB
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 0.5V to 1.6V
Voltage Gain
RCOMP = 1.0 MΩ (Note 6)
Error Amp
VCOMP = 1.0V
3.200
1.800
670
400/200
125
6.000
mmho
V/V
425/600
nA
Input Bias Current
All Output Voltage Versions Electrical Characteristics
(Note 5)
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.
Symbol
IS
Parameters
Input Supply Current
Conditions
Typical
Max
Units
11
15.5/16.5
mA
ISWITCH = 3.0A
85
140/165
mA
VSH = 3V
16
100/300
µA
Switch Off
Min
(Note 8)
IS/D
Shutdown Input
Supply Current
VUV
Input Supply
RLOAD = 100Ω
3.30
3.05
3.75
V
100
85/75
115/125
kHz
Undervoltage Lockout
fO
Oscillator Frequency
Measured at Switch Pin
RLOAD = 100Ω, VCOMP = 1.0V
Freq. Adj. Pin Open (Pin 1)
RSET = 22 kΩ
fSC
Short-Circuit
Measured at Switch Pin
Frequency
RLOAD = 100Ω
200
kHz
25
kHz
VFEEDBACK = 1.15V
VEAO
Error Amplifier
Upper Limit
Output Swing
(Note 7)
2.8
Lower Limit
2.6/2.4
0.25
V
0.40/0.55
V
(Note 8)
IEAO
Error Amp
(Note 9)
Output Current
165
110/70
260/320
µA
11.0
8.0/7.0
17.0/19.0
µA
98
93/90
(Source or Sink)
ISS
Soft Start Current
DMAX
Maximum Duty Cycle
VFEEDBACK = 0.92V
VCOMP = 1.0V
RLOAD = 100Ω
%
(Note 7)
IL
Switch Leakage
Switch Off
Current
VSWITCH = 60V
VSUS
Switch Sustaining
Voltage
dV/dT = 1.5V/ns
VSAT
Switch Saturation
Voltage
ISWITCH = 5.0A
15
300/600
65
0.7
5
µA
V
1.1/1.4
V
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LM2588
LM2588-ADJ Electrical Characteristics
LM2588
All Output Voltage Versions Electrical Characteristics
(Note 5) (Continued)
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.
Symbol
ICL
VSTH
ISYNC
VSHTH
ISH
θJA
Parameters
Conditions
NPN Switch Current
Limit
Synchronization
FSYNC = 200 kHz
Threshold Voltage
VCOMP = 1V, VIN = 5V
Synchronization
VIN = 5V
Pin Current
VCOMP = 1V, VSYNC = VSTH
Typical
Min
Max
Units
6.5
5.0
9.5
A
0.75
0.625/0.40
0.875/1.00
V
200
µA
100
ON /OFF Pin (Pin 1)
VCOMP = 1V
Threshold Voltage
(Note 10)
ON /OFF Pin (Pin 1)
VCOMP = 1V
Current
VSH = VSHTH
Thermal Resistance
T Package, Junction to Ambient
1.6
1.0/0.8
2.2/2.4
V
40
15/10
65/75
µA
65
(Note 11)
θJA
T Package, Junction to Ambient
45
(Note 12)
θJC
T Package, Junction to Case
2
θJA
S Package, Junction to Ambient
56
˚C/W
(Note 13)
θJA
S Package, Junction to Ambient
35
(Note 14)
θJA
S Package, Junction to Ambient
26
(Note 15)
θJC
S Package, Junction to Case
2
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 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 (TJ) is a function of the ambient temperature (TA), the junction-to-ambient thermal resistance (θJA), and the power
dissipation of the device (PD). A thermal shutdown will occur if the temperature exceeds the maximum junction temperature of the device: PD x θJA + TA(MAX) ≥
TJ(MAX). For a safe thermal design, check that the maximum power dissipated by the device is less than: PD ≤ [TJ(MAX) − TA(MAX)]/θJA. When calculating the
maximum 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 Figure 1 and Figure 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
Quality 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 AVOL.
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 LM2588 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: 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.
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LM2588
Typical Performance Characteristics
Supply Current
vs Temperature
Reference Voltage
vs Temperature
01242002
01242003
∆Reference Voltage
vs Supply Voltage
Supply Current
vs Switch Current
01242004
01242005
Current Limit
vs Temperature
Feedback Pin Bias
Current vs Temperature
01242007
01242006
7
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LM2588
Typical Performance Characteristics
(Continued)
Switch Saturation
Voltage vs Temperature
Switch Transconductance
vs Temperature
01242008
01242009
Oscillator Frequency
vs Temperature
Error Amp Transconductance
vs Temperature
01242010
01242011
Error Amp Voltage
Gain vs Temperature
Short Circuit Frequency
vs Temperature
01242012
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01242013
8
LM2588
Typical Performance Characteristics
(Continued)
Shutdown Supply Current
vs Temperature
ON /OFF Pin Current
vs Voltage
01242014
01242015
Oscillator Frequency
vs Resistance
01242016
Flyback Regulator
01242001
9
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LM2588
Test Circuits
01242021
CIN1 — 100 µF, 25V Aluminum ElectrolyticCIN2 — 0.1 µF CeramicT — 22 µH, 1:1 Schott #67141450D — 1N5820COUT — 680 µF, 16V Aluminum
ElectrolyticCC — 0.47 µF CeramicRC — 2k
FIGURE 1. LM2588-3.3 and LM2588-5.0
01242022
CIN1 — 100 µF, 25V Aluminum ElectrolyticCIN2 — 0.1 µF CeramicL — 15 µH, Renco #RL-5472-5D — 1N5820COUT — 680 µF, 16V Aluminum
ElectrolyticCC — 0.47 µF CeramicRC — 2kFor 12V Devices: R1 = Short (0Ω) andR2 = OpenFor ADJ Devices: R1 = 48.75k, ± 0.1% andR2 = 5.62k, ± 0.1%
FIGURE 2. LM2588-12 and LM2588-ADJ
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LM2588
Block Diagram
01242023
For Fixed Versions 3.3V, R1 = 3.4k, R2 = 2k5.0V, R1 = 6.15k, R2 = 2k12V, R1 = 8.73k, R2 = 1kFor Adj. VersionR1 = Short (0Ω), R2 = Open
FIGURE 3. Block Diagram
lapses, reversing the voltage polarity of the primary 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 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 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.
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 Figure 4, or multiple
output 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-
11
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LM2588
Flyback Regulator Operation
(Continued)
01242024
As 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
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
01242060
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
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LM2588
Typical Performance Characteristics
(Continued)
01242061
FIGURE 6. VOUT Response to Load Current Step
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 LM2588-ADJ — or different output
configurations that do not match the standard configurations,
refer to the Switchers Made Simple™ software.
Typical Flyback Regulator
Applications
Figure 7 through 12 show six typical flyback applications,
varying from single output to triple output. Each drawing
contains the part number(s) and manufacturer(s) for every
01242025
FIGURE 7. Single-Output Flyback Regulator
13
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LM2588
Typical Flyback Regulator Applications
(Continued)
01242026
FIGURE 8. Single-Output Flyback Regulator
01242027
FIGURE 9. Single-Output Flyback Regulator
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LM2588
Typical Flyback Regulator Applications
(Continued)
01242028
FIGURE 10. Dual-Output Flyback Regulator
01242029
FIGURE 11. Dual-Output Flyback Regulator
15
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LM2588
Typical Flyback Regulator Applications
(Continued)
01242030
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
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Transformers
T1
T1
T1
T2
T3
T4
18V–36V
VIN
4V–6V
4V–6V
8V–16V
4V–6V
18V–36V
VOUT1
3.3V
5V
12V
12V
12V
5V
IOUT1 (Max)
1.8A
1.4A
1.2A
0.3A
1A
2.5A
1
1
1
0.35
N1
2.5
0.8
VOUT2
−12V
−12V
12V
IOUT2 (Max)
0.3A
1A
0.5A
2.5
0.8
N2
0.8
VOUT3
−12V
IOUT3 (Max)
0.5A
N3
0.8
FIGURE 13. Transformer Selection Table
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Transformer
Type
LM2588
Typical Flyback Regulator Applications
(Continued)
Manufacturers’ Part Numbers
Coilcraft
Coilcraft (Note 16)
Pulse (Note 17)
Renco
Schott
(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: (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:
Note 17: Pulse Engineering Inc.,:
12220 World Trade Drive, San Diego, CA 92128:
European Headquarters, Dunmore Road:
Tuam, Co. Galway, Ireland:
Fax: (619) 674-8262
Phone: +353 93 24 107
Fax: +353 93 24 459
Note 18: Renco Electronics Inc.,:
Phone: (800) 645-5828
60 Jeffryn Blvd. East, Deer Park, NY 11729:
Note 19: Schott Corp.,:
Fax: +44 1236 730 627
Phone: (619) 674-8100
Fax: (516) 586-5562
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 32 show the footprints of each transformer, listed in Figure 14.
T3
T1
01242033
Top View
01242031
Top View
FIGURE 17. Coilcraft Q4343-B
FIGURE 15. Coilcraft Q4434-B
T4
T2
01242032
Top View
01242034
Top View
FIGURE 16. Coilcraft Q4337-B
FIGURE 18. Coilcraft Q4344-B
17
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LM2588
Typical Flyback Regulator
Applications (Continued)
T2
T1
01242038
Top View
01242035
Top View
FIGURE 22. Pulse PE-68412
(Surface Mount)
FIGURE 19. Coilcraft Q4435-B
(Surface Mount)
T3
T2
01242039
Top View
01242036
Top View
FIGURE 23. Pulse PE-68421
(Surface Mount)
FIGURE 20. Coilcraft Q4436-B
(Surface Mount)
T4
T1
01242040
Top View
01242037
Top View
FIGURE 24. Pulse PE-68422
(Surface Mount)
FIGURE 21. Pulse PE-68411
(Surface Mount)
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18
LM2588
Typical Flyback Regulator
Applications (Continued)
T1
T1
01242045
Top View
FIGURE 29. Schott 67141450
01242041
Top View
T2
FIGURE 25. Renco RL-5530
T2
01242046
Top View
FIGURE 30. Schott 67140860
01242042
Top View
T3
FIGURE 26. Renco RL-5531
T3
01242047
Top View
FIGURE 31. Schott 67140920
01242043
Top View
FIGURE 27. Renco RL-5534
T4
01242044
Top View
FIGURE 28. Renco RL-5535
19
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LM2588
Typical Flyback Regulator Applications
(Continued)
T4
01242048
Top View
FIGURE 32. Schott 67140930
VIN/L, storing energy in the inductor. When the switch turns
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
inductor during the switch on time is transferred to the output
during the switch off time. The output voltage is controlled by
adjusting the peak switch current, as described in the flyback
regulator section.
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
01242049
FIGURE 33. 12V Boost Regulator
By adding a small number of external components (as
shown in Figure 33), the LM2588 can be used to produce a
regulated output voltage that is greater than the applied input
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voltage. The switching waveforms observed during the operation of this circuit are shown in Figure 34. Typical performance of this regulator is shown in Figure 35.
20
LM2588
Typical Performance Characteristics
01242062
A: Switch Voltage,10V/div
B: Switch Current, 5A/div
C: Inductor Current, 5A/div
D: Output Ripple Voltage,
100 mV/div, AC-Coupled
FIGURE 34. Switching Waveforms
01242063
FIGURE 35. VOUT Response to Load Current Step
ber(s) and manufacturer(s) for every component. For the
fixed 12V output application, the part numbers and manufacturers’ names for the inductor are listed in a table in Figure
37. For applications with different output voltages, refer to
the Switchers Made Simplesoftware.
Typical Boost Regulator
Applications
Figure 36 and 38 through 40 show four typical boost
applications — one fixed and three using the adjustable version of the LM2588. Each drawing contains the part num-
21
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LM2588
Typical Boost Regulator Applications
(Continued)
01242050
FIGURE 36. +5V to +12V Boost Regulator
Figure 37 contains a table of standard inductors, by part
number and corresponding manufacturer, for the fixed output regulator of Figure 36.
Note 20: Coilcraft Inc.,:
Coilcraft (Note 20)
Pulse (Note 21)
Renco (Note 22)
Schott (Note 23)
R4793-A
PE-53900
RL-5472-5
67146520
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:
Note 21: Pulse Engineering Inc.,:
12220 World Trade Drive, San Diego, CA 92128:
European Headquarters, Dunmore Road:
Tuam, Co. Galway, Ireland:
Fax: (619) 674-8262
Phone: +353 93 24 107
Fax: +353 93 24 459
Note 22: Renco Electronics Inc.,:
Phone: (800) 645-5828
60 Jeffryn Blvd. East, Deer Park, NY 11729:
Note 23: Schott Corp.,:
Fax: +44 1236 730 627
Phone: (619) 674-8100
Fax: (516) 586-5562
Phone: (612) 475-1173
1000 Parkers Lane Road, Wayzata, MN 55391:
Fax: (612) 475-1786
FIGURE 37. Inductor Selection Table
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22
LM2588
Typical Boost Regulator Applications
(Continued)
01242051
FIGURE 38. +12V to +24V Boost Regulator
01242052
FIGURE 39. +24V to +36V Boost Regulator
23
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LM2588
Typical Boost Regulator Applications
(Continued)
01242053
*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.
FIGURE 40. +24V to +48V Boost Regulator
FREQUENCY ADJUSTMENT
The switching frequency of the LM2588 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 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 can be used to adjust the
frequency 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 42 shows resistor values corresponding to
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.
Application Hints
LM2588 SPECIAL FEATURES
01242054
RSET(kΩ)
FIGURE 41. Shutdown Operation
SHUTDOWN CONTROL
A feature of the LM2588 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
operation, an isolation diode is required (as shown in Figure
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 VIN and 40 µA to the ON /OFF pin). To turn the
device back on, leave pin 1 floating, using an (isolation)
diode, as shown in Figure 41 (for normal operation, do not
source or sink current to or from this pin — see the next
section).
Frequency (kHz)
Open
100
200
125
47
150
33
175
22
200
FIGURE 42. Frequency Setting Resistor Guide
01242055
FIGURE 43. Frequency Synchronization
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24
PROGRAMMING OUTPUT VOLTAGE
(SELECTING R1 AND R2)
Referring to the adjustable regulator in Figure 45, the output
voltage is programmed by the resistors R1 and R2 by the
following formula:
where VREF = 1.23V
VOUT = VREF (1 + R1/R2)
(Continued)
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.
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)
A negative falling pulse applied to the sync pin will synchronize the LM2588 to an external oscillator (see Figure 43 and
44).
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.
For best temperature coefficient and stability with time, use
1% metal film resistors.
SHORT CIRCUIT CONDITION
Due to the inherent nature of 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
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 limit circuit. The external limit should
be set to the maximum switch current of the device, which is
5A.
In a flyback regulator application (Figure 46 ), using the
standard transformers, the LM2588 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
before the switch turns back on. Hence, the switch turns on
initially with zero current at its collector. In this condition, the
switch current limit will limit the peak current, saving the
device.
01242064
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 edge of the sync signal and the
turning on of the switch.
01242056
FIGURE 45. Boost Regulator
25
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LM2588
Application Hints
LM2588
Application Hints
(Continued)
01242057
FIGURE 46. Flyback Regulator
and 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.
FLYBACK REGULATOR INPUT CAPACITORS
A flyback regulator draws discontinuous pulses of current
from the input supply. Therefore, there are two input capacitors needed in a flyback regulator — one for energy storage
and one for filtering (see Figure 46). 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) is required. If the input source 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
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 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.
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 as well. When used in 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 capacitance and the
transformer leakage inductance forming a 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. One is to add an RC snubber around the
output rectifier(s), as in Figure 46. 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.
The other method to reduce or eliminate the “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 reverse voltage
rating of the diode must be greater than the switch off
voltage.
SWITCH VOLTAGE LIMITS
In a flyback regulator, the maximum steady-state voltage
appearing at the switch, when it is off, is set by the transformer turns ratio, N, the output voltage, VOUT, and the
maximum input 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 ultrafast 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
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 in the circuit in Figure 4
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26
former. 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).
(Continued)
NOISY INPUT LINE CONDITION
A small, low-pass RC filter should be used at the input pin 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 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 application. If efficiency is a major concern, replace the resistor with
a small inductor (say 10 µH and rated at 200 mA).
01242058
STABILITY
FIGURE 47. Input Line Filter
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:
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:
VOUT ≈ N x VIN x D/(1 − D)
The duty cycle of a flyback regulator is determined by the
following equation:
where VSAT is the switch saturation voltage and can be
found in the Characteristic Curves.
Theoretically, the maximum output voltage can be as large
as desired — just keep increasing the turns ratio of the trans-
01242059
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 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
indicated in Figure 48). When using the Adjustable version,
physically locate the programming resistors as near the
regulator IC as possible, to keep the sensitive feedback
wiring short.
27
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LM2588
Application Hints
LM2588
Application Hints
HEAT SINK/THERMAL CONSIDERATIONS
Adding the junction temperature rise to the maximum ambient temperature gives the actual operating junction temperature:
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).
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:
∆TJ = PD • (θJC + θInterface + θHeat Sink)
(Continued)
TJ = ∆TJ + TA.
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 θJA and θJC (given
in the Electrical Characteristics).
Total power dissipated (PD) by the LM2588 can be estimated
as follows:
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).
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 resistance required to maintain the
regulator junction temperature below the maximum operating temperature.
Boost:
To further simplify the flyback regulator design procedure,
National Semiconductor is making available computer design software Switchers Made Simple. Software is available
on a (31⁄2") 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).
VIN is the minimum input voltage, VOUT is the output voltage,
N is the transformer turns ratio, D is the duty cycle, and ILOAD
is the maximum load current (and ∑ILOAD is the sum of the
maximum load currents for multiple-output flyback regulators). The duty cycle is given by:
Boost:
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.
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28
LM2588
Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number LM2588T-3.3, LM2588T-5.0,
LM2588T-12 or LM2588T-ADJ
NS Package Number TA07B
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
29
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LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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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 or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
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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.
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