NSC LM1577 Simple switcherâ® step-up voltage regulator Datasheet

LM1577/LM2577
SIMPLE SWITCHER ® Step-Up Voltage Regulator
General Description
Features
The LM1577/LM2577 are monolithic integrated circuits that
provide all of the power and control functions for step-up
(boost), flyback, and forward converter switching regulators.
The device is available in three different output voltage
versions: 12V, 15V, and adjustable.
Requiring a minimum number of external components, these
regulators are cost effective, and simple to use. Listed in this
data sheet are a family of standard inductors and flyback
transformers designed to work with these switching regulators.
Requires few external components
NPN output switches 3.0A, can stand off 65V
Wide input voltage range: 3.5V to 40V
Current-mode operation for improved transient
response, line regulation, and current limit
n 52 kHz internal oscillator
n Soft-start function reduces in-rush current during start-up
n Output switch protected by current limit, under-voltage
lockout, and thermal shutdown
Included on the chip is a 3.0A NPN switch and its associated
protection circuitry, consisting of current and thermal limiting,
and undervoltage lockout. Other features include a 52 kHz
fixed-frequency oscillator that requires no external components, a 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.
Typical Applications
n
n
n
n
n Simple boost regulator
n Flyback and forward regulators
n Multiple-output regulator
Connection Diagrams
Straight Leads
5-Lead TO-220 (T)
Bent, Staggered Leads
5-Lead TO-220 (T)
01146804
Top View
Order Number LM2577T-12, LM2577T-15,
or LM2577T-ADJ
See NS Package Number T05A
01146805
Top View
Order Number LM2577T-12 Flow LB03, LM2577T-15
Flow LB03, or LM2577T-ADJ Flow LB03
See NS Package Number T05D
SIMPLE SWITCHER ® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation
DS011468
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LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
April 2005
LM1577/LM2577
Connection Diagrams
(Continued)
16-Lead DIP (N)
24-Lead Surface Mount (M)
01146806
*No internal Connection
Top View
Order Number LM2577N-12, LM2577N-15,
or LM2577N-ADJ
See NS Package Number N16A
01146807
*No internal Connection
Top View
Order Number LM2577M-12, LM2577M-15,
or LM2577M-ADJ
See NS Package Number M24B
TO-263 (S)
5-Lead Surface-Mount Package
01146833
Side View
Order Number LM2577S-12, LM2577S-15,
or LM2577S-ADJ
See NS Package Number TS5B
01146832
Top View
4-Lead TO-3 (K)
01146808
Bottom View
Order Number LM1577K-12/883, LM1577K-15/883,
or LM1577K-ADJ/883
See NS Package Number K04A
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2
Temperature
Range
Package
Type
Output Voltage
12V
15V
NSC
ADJ
Package
Package
Drawing
−40˚C ≤ TA ≤ +125˚C
24-Pin Surface
Mount
LM2577M-12
LM2577M-15
LM2577M-ADJ
M24B
SO
16-Pin Molded DIP
LM2577N-12
LM2577N-15
LM2577N-ADJ
N16A
N
5-Lead Surface
Mount
LM2577S-12
LM2577S-15
LM2577S-ADJ
TS5B
TO-263
5-Straight Leads
LM2577T-12
LM2577T-15
LM2577T-ADJ
T05A
TO-220
5-Bent Staggered
LM2577T-12
LM2577T-15
LM2577T-ADJ
T05D
TO-220
Flow LB03
Flow LB03
Flow LB03
K04A
TO-3
Leads
−55˚C ≤ TA ≤ +150˚C
4-Pin TO-3
LM1577K-12/883LM1577K-15/883
LM1577KADJ/883
Typical Application
01146801
Note: Pin numbers shown are for TO-220 (T) package.
3
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LM1577/LM2577
Ordering Information
LM1577/LM2577
Absolute Maximum Ratings (Note 1)
Minimum ESD Rating
(C = 100 pF, R = 1.5 kΩ)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
2 kV
Operating Ratings
Supply Voltage
45V
Output Switch Voltage
65V
Supply Voltage
6.0A
Output Switch Voltage
0V ≤ VSWITCH ≤ 60V
Internally Limited
Output Switch Current
ISWITCH ≤ 3.0A
−65˚C to +150˚C
Junction Temperature Range
Output Switch Current (Note 2)
Power Dissipation
Storage Temperature Range
Lead Temperature
(Soldering, 10 sec.)
260˚C
Maximum Junction Temperature
3.5V ≤ VIN ≤ 40V
LM1577
−55˚C ≤ TJ ≤ +150˚C
LM2577
−40˚C ≤ TJ ≤ +125˚C
150˚C
Electrical Characteristics—LM1577-12, LM2577-12
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, and ISWITCH = 0.
Symbol
Parameter
Conditions
Typical
LM1577-12
LM2577-12
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
11.60/11.40
11.60/11.40
V(min)
12.40/12.60
12.40/12.60
V(max)
SYSTEM PARAMETERS Circuit of Figure 1 (Note 6)
VOUT
Output Voltage
VIN = 5V to 10V
12.0
ILOAD = 100 mA to 800 mA
(Note 3)
Line Regulation
VIN = 3.5V to 10V
20
ILOAD = 300 mA
Load Regulation
Efficiency
mV
50/100
VIN = 5V
50/100
20
ILOAD = 100 mA to 800 mA
η
V
mV(max)
mV
50/100
50/100
mV(max)
VIN = 5V, ILOAD = 800 mA
80
%
VFEEDBACK = 14V (Switch Off)
7.5
mA
ISWITCH = 2.0A
25
DEVICE PARAMETERS
IS
Input Supply Current
VCOMP = 2.0V (Max Duty Cycle)
VUV
Input Supply
ISWITCH = 100 mA
Oscillator Frequency
Measured at Switch Pin
Output Reference
Measured at Feedback Pin
Voltage
VIN = 3.5V to 40V
50/85
50/85
mA(max)
2.70/2.65
2.70/2.65
V(min)
3.10/3.15
3.10/3.15
V(max)
mA
12
VIN = 3.5V to 40V
V
kHz
48/42
48/42
kHz(min)
56/62
56/62
kHz(max)
V
VCOMP = 1.0V
Output Reference
mA(max)
52
ISWITCH = 100 mA
VREF
10.0/14.0
2.90
Undervoltage Lockout
fO
10.0/14.0
11.76/11.64
11.76/11.64
V(min)
12.24/12.36
12.24/12.36
V(max)
7
mV
9.7
kΩ
Voltage Line Regulator
RFB
Feedback Pin Input
Resistance
GM
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Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
4
370
µmho
225/145
225/145
µmho(min)
515/615
515/615
µmho(max)
(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, and ISWITCH = 0.
Symbol
Parameter
Conditions
Typical
LM1577-12
LM2577-12
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
DEVICE PARAMETERS
AVOL
Error Amp
Voltage Gain
VCOMP = 1.1V to 1.9V
80
RCOMP = 1.0 MΩ
V/V
50/25
50/25
V/V(min)
2.2/2.0
2.2/2.0
V(min)
0.40/0.55
0.40/0.55
V(max)
(Note 7)
Error Amplifier
Upper Limit
Output Swing
VFEEDBACK = 10.0V
2.4
Lower Limit
0.3
VFEEDBACK = 15.0V
ISS
Error Amplifier
VFEEDBACK = 10.0V to 15.0V
Output Current
VCOMP = 1.0V
Soft Start Current
Maximum Duty Cycle
VFEEDBACK = 10.0V
± 130/ ± 90
± 300/ ± 400
5.0
VCOMP = 1.5V
2.5/1.5
2.5/1.5
µA(min)
7.5/9.5
7.5/9.5
µA(max)
93/90
93/90
%(min)
%
12.5
Switch Leakage
VSWITCH = 65V
Current
VFEEDBACK = 15V (Switch Off)
Switch Saturation
ISWITCH = 2.0A
Voltage
VCOMP = 2.0V (Max Duty Cycle)
A/V
10
µA
300/600
300/600
0.5
NPN Switch
µA(max)
V
0.7/0.9
0.7/0.9
V(max)
3.7/3.0
3.7/3.0
A(min)
5.3/6.0
5.3/6.0
A(max)
4.5
Current Limit
µA(min)
µA(max)
µA
95
Switch
Transconductance
VSAT
µA
± 130/ ± 90
± 300/ ± 400
ISWITCH = 100 mA
IL
V
± 200
VCOMP = 0V
D
V
A
Electrical Characteristics—LM1577-15, LM2577-15
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, and ISWITCH = 0.
Symbol
Parameter
Conditions
Typical
LM1577-15
LM2577-15
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
SYSTEM PARAMETERS Circuit of Figure 2 (Note 6)
VOUT
Output Voltage
Line Regulation
VIN = 5V to 12V
15.0
ILOAD = 100 mA to 600 mA
14.50/14.25
14.50/14.25
V(min)
(Note 3)
15.50/15.75
15.50/15.75
V(max)
50/100
50/100
50/100
50/100
VIN = 3.5V to 12V
20
ILOAD = 300 mA
Load Regulation
VIN = 5V
Efficiency
mV
20
ILOAD = 100 mA to 600 mA
η
V
VIN = 5V, ILOAD = 600 mA
5
80
mV(max)
mV
mV(max)
%
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LM1577/LM2577
Electrical Characteristics—LM1577-12, LM2577-12
LM1577/LM2577
Electrical Characteristics—LM1577-15, LM2577-15
(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, and ISWITCH = 0.
Symbol
Parameter
Conditions
Typical
LM1577-15
LM2577-15
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
DEVICE PARAMETERS
IS
Input Supply Current
VFEEDBACK = 18.0V
7.5
(Switch Off)
mA
10.0/14.0
10.0/14.0
mA(max)
50/85
50/85
mA(max)
Undervoltage
2.70/2.65
2.70/2.65
V(min)
Lockout
3.10/3.15
3.10/3.15
V(max)
48/42
48/42
kHz(min)
56/62
56/62
kHz(max)
14.70/14.55
14.70/14.55
V(min)
15.30/15.45
15.30/15.45
V(max)
ISWITCH = 2.0A
25
VCOMP = 2.0V
mA
(Max Duty Cycle)
VUV
fO
Input Supply
Oscillator Frequency
ISWITCH = 100 mA
2.90
Measured at Switch Pin
52
ISWITCH = 100 mA
VREF
Output Reference
Measured at Feedback Pin
Voltage
VIN = 3.5V to 40V
Output Reference
VIN = 3.5V to 40V
V
kHz
V
15
VCOMP = 1.0V
10
mV
12.2
kΩ
300
µmho
Voltage Line Regulation
RFB
Feedback Pin Input
Voltage Line Regulator
GM
AVOL
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 1.1V to 1.9V
Voltage Gain
RCOMP = 1.0 MΩ
170/110
170/110
µmho(min)
420/500
420/500
µmho(max)
65
V/V
40/20
40/20
V/V(min)
2.2/2.0
2.2/2.0
V(min)
0.4/0.55
0.40/0.55
V(max)
± 130/ ± 90
± 300/ ± 400
± 130/ ± 90
± 300/ ± 400
µA(max)
2.5/1.5
2.5/1.5
µA(min)
7.5/9.5
7.5/9.5
µA(max)
93/90
93/90
%(min)
(Note 7)
Error Amplifier
Upper Limit
Output Swing
VFEEDBACK = 12.0V
2.4
Lower Limit
0.3
VFEEDBACK = 18.0V
Error Amp
Output Current
ISS
Soft Start Current
VFEEDBACK = 12.0V to 18.0V
VCOMP = 1.0V
VFEEDBACK = 12.0V
Maximum Duty
VCOMP = 1.5V
Cycle
ISWITCH = 100 mA
µA
5.0
%
12.5
Switch Leakage
VSWITCH = 65V
Current
VFEEDBACK = 18.0V
µA(min)
µA
95
Switch
Transconductance
IL
V
± 200
VCOMP = 0V
D
V
A/V
10
µA
300/600
300/600
µA(max)
0.7/0.9
0.7/0.9
V(max)
(Switch Off)
VSAT
Switch Saturation
ISWITCH = 2.0A
Voltage
VCOMP = 2.0V
0.5
(Max Duty Cycle)
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6
V
(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, and ISWITCH = 0.
Symbol
Parameter
Conditions
Typical
LM1577-15
LM2577-15
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
DEVICE PARAMETERS
NPN Switch
VCOMP = 2.0V
4.3
Current Limit
A
3.7/3.0
3.7/3.0
A(min)
5.3/6.0
5.3/6.0
A(max)
Electrical Characteristics—LM1577-ADJ, LM2577-ADJ
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, VFEEDBACK = VREF, and ISWITCH = 0.
LM1577-ADJ LM2577-ADJ
Symbol
Parameter
Conditions
Typical
Units
Limit
Limit
(Notes 3, 4)
(Note 5)
(Limits)
ILOAD = 100 mA to 800 mA
11.60/11.40
11.60/11.40
V(min)
(Note 3)
12.40/12.60
12.40/12.60
V(max)
50/100
50/100
mV(max)
50/100
50/100
mV(max)
SYSTEM PARAMETERS Circuit of Figure 3 (Note 6)
VOUT
∆VOUT/
Output Voltage
Line Regulation
∆VIN
∆VOUT/
12.0
VIN = 3.5V to 10V
Load Regulation
VIN = 5V
mV
20
ILOAD = 100 mA to 800 mA
Efficiency
V
20
ILOAD = 300 mA
∆ILOAD
η
VIN = 5V to 10V
mV
VIN = 5V, ILOAD = 800 mA
80
%
VFEEDBACK = 1.5V (Switch Off)
7.5
mA
ISWITCH = 2.0A
25
DEVICE PARAMETERS
IS
Input Supply Current
VCOMP = 2.0V (Max Duty Cycle)
VUV
Input Supply
ISWITCH = 100 mA
Oscillator Frequency
Measured at Switch Pin
Reference
Measured at Feedback Pin
Voltage
VIN = 3.5V to 40V
∆VREF/
Reference Voltage
Line Regulation
IB
Error Amp
1.230
VIN = 3.5V to 40V
0.5
VCOMP = 1.0V
100
Input Bias Current
GM
AVOL
50/85
50/85
mA(max)
mA
V
2.70/2.65
2.70/2.65
V(min)
3.10/3.15
3.10/3.15
V(max)
kHz
48/42
48/42
kHz(min)
56/62
56/62
kHz(max)
V
VCOMP = 1.0V
∆VIN
mA(max)
52
ISWITCH = 100 mA
VREF
10.0/14.0
2.90
Undervoltage Lockout
fO
10.0/14.0
1.214/1.206
1.214/1.206
V(min)
1.246/1.254
1.246/1.254
V(max)
mV
nA
300/800
Error Amp
ICOMP = −30 µA to +30 µA
Transconductance
VCOMP = 1.0V
Error Amp
VCOMP = 1.1V to 1.9V
Voltage Gain
RCOMP = 1.0 MΩ (Note 7)
300/800
3700
µmho
2400/1600
2400/1600
µmho(min)
4800/5800
4800/5800
µmho(max)
500/250
500/250
V/V(min)
800
7
nA(max)
V/V
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LM1577/LM2577
Electrical Characteristics—LM1577-15, LM2577-15
LM1577/LM2577
Electrical Characteristics—LM1577-ADJ, LM2577-ADJ
(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, VFEEDBACK = VREF, and ISWITCH = 0.
LM1577-ADJ LM2577-ADJ
Symbol
Parameter
Conditions
Typical
Limit
Limit
(Notes 3, 4)
(Note 5)
Units
(Limits)
DEVICE PARAMETERS
Error Amplifier
Upper Limit
Output Swing
VFEEDBACK = 1.0V
2.4
Lower Limit
Error Amp
VFEEDBACK = 1.0V to 1.5V
Output Current
VCOMP = 1.0V
Soft Start Current
Maximum Duty Cycle
∆ISWITCH/
Switch
∆VCOMP
Transconductance
IL
Switch Leakage
V(min)
0.40/0.55
0.40/0.55
V(max)
V
µA
± 130/ ± 90
± 300/ ± 400
VFEEDBACK = 1.0V
± 130/ ± 90
± 300/ ± 400
5.0
VCOMP = 1.5V
2.5/1.5
2.5/1.5
µA(min)
7.5/9.5
7.5/9.5
µA(max)
%
93/90
VSWITCH = 65V
Current
VFEEDBACK = 1.5V (Switch Off)
Switch Saturation
ISWITCH = 2.0A
Voltage
VCOMP = 2.0V (Max Duty Cycle)
NPN Switch
VCOMP = 2.0V
µA(min)
µA(max)
µA
95
ISWITCH = 100 mA
VSAT
2.2/2.0
± 200
VCOMP = 0V
D
2.2/2.0
0.3
VFEEDBACK = 1.5V
ISS
V
93/90
%(min)
12.5
A/V
10
µA
300/600
300/600
µA(max)
0.7/0.9
0.7/0.9
V(max)
3.7/3.0
3.7/3.0
A(min)
5.3/6.0
5.3/6.0
A(max)
0.5
V
4.3
Current Limit
A
THERMAL PARAMETERS (All Versions)
θJA
K Package, Junction to Ambient
35
θJC
Thermal Resistance
K Package, Junction to Case
1.5
θJA
T Package, Junction to Ambient
65
θJC
T Package, Junction to Case
2
θJA
N Package, Junction to
85
Ambient (Note 8)
θJA
M Package, Junction
˚C/W
100
to Ambient (Note 8)
θJA
S Package, Junction to
37
Ambient (Note 9)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions the device is intended to
be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the
Electrical Characteristics.
Note 2: Due to timing considerations of the LM1577/LM2577 current limit circuit, output current cannot be internally limited when the LM1577/LM2577 is used as
a step-up regulator. To prevent damage to the switch, its current must be externally limited to 6.0A. However, output current is internally limited when the
LM1577/LM2577 is used as a flyback or forward converter regulator in accordance to the Application Hints.
Note 3: All limits guaranteed at room temperature (standard type face) and at temperature extremes (boldface type). All limits are used to calculate Outgoing Quality
Level, and are 100% production tested.
Note 4: A military RETS electrical test specification is available on request. At the time of printing, the LM1577K-12/883, LM1577K-15/883, and LM1577K-ADJ/883
RETS specifications complied fully with the boldface limits in these columns. The LM1577K-12/883, LM1577K-15/883, and LM1577K-ADJ/883 may also be procured
to Standard Military Drawing specifications.
Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (boldface type). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods.
Note 6: External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the LM1577/LM2577 is
used as shown in the Test Circuit, system performance will be as specified by the system parameters.
Note 7: A 1.0 MΩ resistor is connected to the compensation pin (which is the error amplifier’s output) to ensure accuracy in measuring AVOL. In actual applications,
this pin’s load resistance should be ≥10 MΩ, resulting in AVOL that is typically twice the guaranteed minimum limit.
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8
(Continued)
Note 8: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper area will lower thermal
resistance further. See thermal model in “Switchers Made Simple” software.
Note 9: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using
0.5 square inches of copper area, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W.
Typical Performance Characteristics
Reference Voltage
vs Temperature
Reference Voltage
vs Temperature
01146834
01146835
∆ Reference Voltage
vs Supply Voltage
Reference Voltage
vs Temperature
01146836
01146837
∆ Reference Voltage
vs Supply Voltage
∆ Reference Voltage
vs Supply Voltage
01146838
01146839
9
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LM1577/LM2577
Electrical Characteristics—LM1577-ADJ, LM2577-ADJ
LM1577/LM2577
Typical Performance Characteristics
(Continued)
Error Amp Transconductance
vs Temperature
Error Amp Transconductance
vs Temperature
01146841
01146840
Error Amp Transconductance
vs Temperature
Error Amp Voltage
Gain vs Temperature
01146843
01146842
Error Amp Voltage
Gain vs Temperature
Error Amp Voltage
Gain vs Temperature
01146844
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01146845
10
LM1577/LM2577
Typical Performance Characteristics
(Continued)
Quiescent Current
vs Temperature
Quiescent Current
vs Switch Current
01146846
01146847
Current Limit
vs Temperature
Current Limit Response
Time vs Overdrive
01146849
01146848
Switch Saturation Voltage
vs Switch Current
Switch Transconductance
vs Temperature
01146851
01146850
11
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LM1577/LM2577
Typical Performance Characteristics
(Continued)
Feedback Pin Bias
Current vs Temperature
Oscillator Frequency
vs Temperature
01146853
01146852
Maximum Power Dissipation
(TO-263) (Note 9)
01146831
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12
LM1577/LM2577
LM1577-12, LM2577-12 Test Circuit
01146830
L = 415-0930 (AIE)
D = any manufacturer
COUT = Sprague Type 673D
Electrolytic 680 µF, 20V
Note: Pin numbers shown are for TO-220 (T) package
FIGURE 1. Circuit Used to Specify System Parameters for 12V Versions
LM1577-15, LM2577-15 Test Circuit
01146826
L = 415-0930 (AIE)
D = any manufacturer
COUT = Sprague Type 673D
Electrolytic 680 µF, 20V
Note: Pin numbers shown are for TO-220 (T) package
FIGURE 2. Circuit Used to Specify System Parameters for 15V Versions
13
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LM1577/LM2577
LM1577-ADJ, LM2577-ADJ Test Circuit
01146809
L = 415-0930 (AIE)
D = any manufacturer
COUT = Sprague Type 673D
Electrolytic 680 µF, 20V
R1 = 48.7k in series with 511Ω (1%)
R2 = 5.62k (1%)
Note: Pin numbers shown are for TO-220 (T) package
FIGURE 3. Circuit Used to Specify System Parameters for ADJ Versions
Application Hints
01146810
Note: Pin numbers shown are for TO-220 (T) package
*Resistors are internal to LM1577/LM2577 for 12V and 15V versions.
FIGURE 4. LM1577/LM2577 Block Diagram and Boost Regulator Application
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14
LM1577/LM2577
Application Hints
(Continued)
Duty Cycle
STEP-UP (BOOST) REGULATOR
Figure 4 shows the LM1577-ADJ/LM2577-ADJ used as a
Step-Up Regulator. This is a switching regulator used for
producing an output voltage greater than the input supply
voltage. The LM1577-12/LM2577-12 and LM1577-15/
LM2577-15 can also be used for step-up regulators with 12V
or 15V outputs (respectively), by tying the feedback pin
directly to the regulator output.
Average
Inductor
Current
A basic explanation of how it works is as follows. The
LM1577/LM2577 turns its output switch on and off at a
frequency of 52 kHz, and this creates energy in the inductor
(L). When the NPN switch turns on, the inductor current
charges up at a rate of VIN/L, storing current 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 the amount of energy transferred which, in turn, is controlled by modulating the peak
inductor 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
voltage proportional to the switch current (i.e., inductor current during the switch on time).
IIND(AVE)
Inductor
Current Ripple
∆IIND
Peak Inductor
Current
IIND(PK)
Peak Switch
Current
ISW(PK)
Switch
Voltage When
Off
VSW(OFF)
VOUT + VF
VR
VOUT − VSAT
Average
Diode Current
ID(AVE)
ILOAD
Peak Diode
Current
ID(PK)
Diode
Reverse
Voltage
Power
Dissipation of
LM1577/2577
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.
D
PD
VF = Forward Biased Diode Voltage
ILOAD = Output Load Current
Voltage and current waveforms for this circuit are shown in
Figure 5, and formulas for calculating them are given in
Figure 6.
FIGURE 6. Step-Up Regulator Formulas
STEP-UP REGULATOR DESIGN PROCEDURE
The following design procedure can be used to select the
appropriate external components for the circuit in Figure 4,
based on these system requirements.
Given:
VIN (min) = Minimum input supply voltage
VOUT = Regulated output voltage
ILOAD(max) = Maximum output load current
Before proceeding any further, determine if the LM1577/
LM2577 can provide these values of VOUT and ILOAD(max)
when operating with the minimum value of VIN. The upper
limits for VOUT and ILOAD(max) are given by the following
equations.
VOUT ≤ 60V
and VOUT ≤ 10 x VIN(min)
01146811
FIGURE 5. Step-Up Regulator Waveforms
These limits must be greater than or equal to the values
specified in this application.
1. Inductor Selection (L)
A. Voltage Options:
1. For 12V or 15V output
From Figure 7 (for 12V output) or Figure 8 (for 15V
output), identify inductor code for region indicated by
VIN (min) and ILOAD (max). The shaded region indicates con15
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LM1577/LM2577
Application Hints
1. Find the lowest value inductor that is greater than LMIN.
2. Find where E • T intersects this inductor value to determine
if it has an L or H prefix. If E • T intersects both the L and H
regions, select the inductor with an H prefix.
(Continued)
ditions for which the LM1577/LM2577 output switch
would be operating beyond its switch current rating. The
minimum operating voltage for the LM1577/LM2577 is
3.5V.
From here, proceed to step C.
2. For Adjustable version
Preliminary calculations:
The inductor selection is based on the calculation of the
following three parameters:
D(max), the maximum switch duty cycle (0 ≤ D ≤ 0.9):
where VF = 0.5V for Schottky diodes and 0.8V for fast
recovery diodes (typically);
E • T, the product of volts x time that charges the inductor:
01146827
FIGURE 7. LM2577-12 Inductor Selection Guide
IIND,DC, the average inductor current under full load;
B. Identify Inductor Value:
1. From Figure 9, identify the inductor code for the
region indicated by the intersection of E • T and IIND,DC.
This code gives the inductor value in microhenries. The
L or H prefix signifies whether the inductor is rated for a
maximum E • T of 90 V • µs (L) or 250 V • µs (H).
2. If D < 0.85, go on to step C. If D ≥ 0.85, then calculate
the minimum inductance needed to ensure the switching
regulator’s stability:
01146828
FIGURE 8. LM2577-15 Inductor Selection Guide
If LMIN is smaller than the inductor value found in step B1, go
on to step C. Otherwise, the inductor value found in step B1
is too low; an appropriate inductor code should be obtained
from the graph as follows:
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16
LM1577/LM2577
Application Hints
(Continued)
01146812
Note: These charts assume that the inductor ripple current inductor is approximately 20% to 30% of the average inductor current (when the regulator is under
full load). Greater ripple current causes higher peak switch currents and greater output ripple voltage; lower ripple current is achieved with larger-value
inductors. The factor of 20 to 30% is chosen as a convenient balance between the two extremes.
FIGURE 9. LM1577-ADJ/LM2577-ADJ Inductor Selection Graph
C. Select an inductor from the table of Figure 10 which
cross-references the inductor codes to the part numbers
of three different manufacturers. Complete specifications
for these inductors are available from the respective
manufacturers. The inductors listed in this table have the
following characteristics:
AIE: ferrite, pot-core inductors; Benefits of this type are
low electro-magnetic interference (EMI), small physical
size, and very low power dissipation (core loss). Be
careful not to operate these inductors too far beyond their
maximum ratings for E • T and peak current, as this will
saturate the core.
Pulse: powdered iron, toroid core inductors; Benefits are
low EMI and ability to withstand E • T and peak current
above rated value better than ferrite cores.
Renco: ferrite, bobbin-core inductors; Benefits are low
cost and best ability to withstand E • T and peak current
above rated value. Be aware that these inductors generate more EMI than the other types, and this may interfere
with signals sensitive to noise.
17
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LM1577/LM2577
Application Hints
Inductor
C. Calculate the minimum value of CC .
(Continued)
Manufacturer’s Part Number
Code
Schott
Pulse
Renco
L47
67126980
PE - 53112
RL2442
RL2443
L68
67126990
PE - 92114
L100
67127000
PE - 92108
RL2444
L150
67127010
PE - 53113
RL1954
L220
67127020
PE - 52626
RL1953
L330
67127030
PE - 52627
RL1952
L470
67127040
PE - 53114
RL1951
L680
67127050
PE - 52629
RL1950
H150
67127060
PE - 53115
RL2445
H220
67127070
PE - 53116
RL2446
H330
67127080
PE - 53117
RL2447
H470
67127090
PE - 53118
RL1961
H680
67127100
PE - 53119
RL1960
H1000
67127110
PE - 53120
RL1959
H1500
67127120
PE - 53121
RL1958
H2200
67127130
PE - 53122
RL2448
The compensation capacitor is also part of the soft start
circuitry. When power to the regulator is turned on, the
switch duty cycle is allowed to rise at a rate controlled by this
capacitor (with no control on the duty cycle, it would immediately rise to 90%, drawing huge currents from the input
power supply). In order to operate properly, the soft start
circuit requires CC ≥ 0.22 µF.
The value of the output filter capacitor is normally large
enough to require the use of aluminum electrolytic capacitors. Figure 11 lists several different types that are recommended for switching regulators, and the following parameters are used to select the proper capacitor.
Working Voltage (WVDC): Choose a capacitor with a working voltage at least 20% higher than the regulator output
voltage.
Ripple Current: This is the maximum RMS value of current
that charges the capacitor during each switching cycle. For
step-up and flyback regulators, the formula for ripple current
is
Schott Corp., (612) 475-1173
1000 Parkers Lake Rd., Wayzata, MN 55391
Pulse Engineering, (619) 268-2400
P.O. Box 12235, San Diego, CA 92112
Renco Electronics Inc., (516) 586-5566
60 Jeffryn Blvd. East, Deer Park, NY 11729
Choose a capacitor that is rated at least 50% higher than this
value at 52 kHz.
FIGURE 10. Table of Standardized Inductors and
Manufacturer’s Part Numbers
Equivalent Series Resistance (ESR) : This is the primary
cause of output ripple voltage, and it also affects the values
of RC and CC needed to stabilize the regulator. As a result,
the preceding calculations for CC and RC are only valid if
ESR doesn’t exceed the maximum value specified by the
following equations.
2. Compensation Network (RC, CC) and Output Capacitor
(COUT) Selection
RC and CC form a pole-zero compensation network that
stabilizes the regulator. The values of RC and CC are mainly
dependant on the regulator voltage gain, ILOAD(max), L and
COUT. The following procedure calculates values for RC, CC,
and COUT that ensure regulator stability. Be aware that this
procedure doesn’t necessarily result in RC and CC that provide optimum compensation. In order to guarantee optimum
compensation, one of the standard procedures for testing
loop stability must be used, such as measuring VOUT transient response when pulsing ILOAD (see Figure 15).
A. First, calculate the maximum value for RC.
Select a capacitor with ESR, at 52 kHz, that is less than or
equal to the lower value calculated. Most electrolytic capacitors specify ESR at 120 Hz which is 15% to 30% higher than
at 52 kHz. Also, be aware that ESR increases by a factor of
2 when operating at −20˚C.
In general, low values of ESR are achieved by using large
value capacitors (C ≥ 470 µF), and capacitors with high
WVDC, or by paralleling smaller-value capacitors.
Select a resistor less than or equal to this value, and it
should also be no greater than 3 kΩ.
B. Calculate the minimum value for COUT using the following
two equations.
The larger of these two values is the minimum value that
ensures stability.
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18
(Continued)
If the LM1577 is located far from the supply source filter
capacitors, an additional large electrolytic capacitor (e.g.
47 µF) is often required.
3. Output Voltage Selection (R1 and R2)
This section is for applications using the LM1577-ADJ/
LM2577-ADJ. Skip this section if the LM1577-12/LM2577-12
or LM1577-15/LM2577-15 is being used.
5. Diode Selection (D)
The switching diode used in the boost regulator must withstand a reverse voltage equal to the circuit output voltage,
and must conduct the peak output current of the LM2577. A
suitable diode must have a minimum reverse breakdown
voltage greater than the circuit output voltage, and should be
rated for average and peak current greater than ILOAD(max)
and ID(PK). Schottky barrier diodes are often favored for use
in switching regulators. Their low forward voltage drop allows
higher regulator efficiency than if a (less expensive) fast
recovery diode was used. See Figure 12 for recommended
part numbers and voltage ratings of 1A and 3A diodes.
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
VOUT = 1.23V (1 + R1/R2)
Resistors R1 and R2 divide the output down so it can be
compared with the LM1577-ADJ/LM2577-ADJ internal
1.23V reference. For a given desired output voltage VOUT,
select R1 and R2 so that
VOUT
4. Input Capacitor Selection (CIN)
The switching action in the step-up regulator causes a triangular ripple current to be drawn from the supply source. This
in turn causes noise to appear on the supply voltage. For
proper operation of the LM1577, the input voltage should be
decoupled. Bypassing the Input Voltage pin directly to
ground with a good quality, low ESR, 0.1 µF capacitor (leads
as short as possible) is normally sufficient.
1A
3A
20V
1N5817
1N5820
MBR120P
MBR320P
40V
P.O. Box 128, Pickens, SC 29671
(803) 878-6311
Fast Recovery
(max)
30V
Cornell Dublier — Types 239, 250, 251, UFT,
300, or 350
Schottky
50V
Nichicon — Types PF, PX, or PZ
1N5818
1N5821
MBR130P
MBR330P
11DQ03
31DQ03
1N5819
1N5822
MBR140P
MBR340P
1A
11DQ04
31DQ04
MBR150
MBR350
1N4933
11DQ05
31DQ05
MUR105
1N4934
927 East Parkway,
Schaumburg, IL 60173
(708) 843-7500
100V
Sprague — Types 672D, 673D, or 674D
3A
MR851
HER102
30DL1
MUR110
MR831
10DL1
HER302
FIGURE 12. Diode Selection Chart
Box 1, Sprague Road,
Lansing, NC 28643
(919) 384-2551
BOOST REGULATOR CIRCUIT EXAMPLE
By adding a few external components (as shown in Figure
13), the LM2577 can be used to produce a regulated output
voltage that is greater than the applied input voltage. Typical
performance of this regulator is shown in Figure 14 and
Figure 15. The switching waveforms observed during the
operation of this circuit are shown in Figure 16.
United Chemi-Con — Types LX, SXF, or SXJ
9801 West Higgins Road,
Rosemont, IL 60018
(708) 696-2000
FIGURE 11. Aluminum Electrolytic Capacitors
Recommended for Switching Regulators
19
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LM1577/LM2577
Application Hints
LM1577/LM2577
Application Hints
(Continued)
01146813
Note: Pin numbers shown are for TO-220 (T) package.
FIGURE 13. Step-up Regulator Delivers 12V from a 5V Input
01146814
FIGURE 14. Line Regulation (Typical) of Step-Up Regulator of Figure 13
01146816
A: Switch pin voltage, 10 V/div
01146815
A: Output Voltage Change, 100 mV/div. (AC-coupled)
B: Switch pin current, 2 A/div
B: Load current, 0.2 A/div
C: Inductor current, 2 A/div
Horizontal: 5 ms/div
D: Output ripple voltage, 100 mV/div (AC-coupled)
Horizontal: 5 µs/div
FIGURE 15. Load Transient Response of Step-Up
Regulator of Figure 13
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FIGURE 16. Switching Waveforms of Step-Up
Regulator of Figure 13
20
A. First, calculate the maximum value for RC.
(Continued)
FLYBACK REGULATOR
A Flyback regulator can produce single or multiple output
voltages that are lower or greater than the input supply
voltage. Figure 18 shows the LM1577/LM2577 used as a
flyback regulator with positive and negative regulated outputs. Its operation is similar to a step-up regulator, except the
output switch contols the primary current of a flyback transformer. Note that the primary and secondary windings are
out of phase, so no current flows through secondary when
current flows through the primary. This allows the primary to
charge up the transformer core when the switch is on. When
the switch turns off, the core discharges by sending current
through the secondary, and this produces voltage at the
outputs. The output voltages are controlled by adjusting the
peak primary current, as described in the step-up regulator
section.
Where ∑ILOAD(max) is the sum of the load current (magnitude) required from both outputs. Select a resistor less than
or equal to this value, and no greater than 3 kΩ.
B. Calculate the minimum value for ∑COUT (sum of COUT
at both outputs) using the following two equations.
Voltage and current waveforms for this circuit are shown in
Figure 17, and formulas for calculating them are given in
Figure 19.
The larger of these two values must be used to ensure
regulator stability.
FLYBACK REGULATOR DESIGN PROCEDURE
1. Transformer Selection
A family of standardized flyback transformers is available for
creating flyback regulators that produce dual output voltages, from ± 10V to ± 15V, as shown in Figure 18. Figure
20lists these transformers with the input voltage, output
voltages and maximum load current they are designed for.
2. Compensation Network (CC, RC) and
Output Capacitor (COUT) Selection
As explained in the Step-Up Regulator Design Procedure,
CC, RC and COUT must be selected as a group. The following
procedure is for a dual output flyback regulator with equal
turns ratios for each secondary (i.e., both output voltages
have the same magnitude). The equations can be used for a
single output regulator by changing ∑ILOAD(max) to ILOAD(max)
in the following equations.
01146817
FIGURE 17. Flyback Regulator Waveforms
21
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LM1577/LM2577
Application Hints
LM1577/LM2577
Application Hints
(Continued)
01146818
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 18. LM1577-ADJ/LM2577-ADJ Flyback Regulator with ± Outputs
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22
LM1577/LM2577
Application Hints
(Continued)
Duty Cycle
D
Primary Current Variation
∆IP
Peak Primary Current
IP(PK)
Switch Voltage when Off
VSW(OFF)
Diode Reverse Voltage
VR
VOUT+ N (VIN− VSAT)
Average Diode Current
ID(AVE)
ILOAD
Peak Diode Current
ID(PK)
Short Circuit Diode Current
Power Dissipation of
LM1577/LM2577
PD
01146878
FIGURE 19. Flyback Regulator Formulas
VOUT = 1.23V (1 + R1/R2)
Resistors R1 and R2 divide the output voltage down so it can
be compared with the LM1577-ADJ/LM2577-ADJ internal
1.23V reference. For a desired output voltage VOUT, select
R1 and R2 so that
C. Calculate the minimum value of CC
D. Calculate the maximum ESR of the +VOUT and −VOUT
output capacitors in parallel.
4. Diode Selection
The switching diode in a flyback converter must withstand
the reverse voltage specified by the following equation.
This formula can also be used to calculate the maximum
ESR of a single output regulator.
At this point, refer to this same section in the Step-Up
Regulator Design Procedurefor more information regarding the selection of COUT.
3. Output Voltage Selection
This section is for applications using the LM1577-ADJ/
LM2577-ADJ. Skip this section if the LM1577-12/LM2577-12
or LM1577-15/LM2577-15 is being used.
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
A suitable diode must have a reverse voltage rating greater
than this. In addition it must be rated for more than the
average and peak diode currents listed in Figure 19.
5. Input Capacitor Selection
The primary of a flyback transformer draws discontinuous
pulses of current from the input supply. As a result, a flyback
regulator generates more noise at the input supply than a
23
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LM1577/LM2577
Application Hints
ber consists of a fast recovery diode, and a parallel RC. The
RC values are selected for switch clamp voltage (VCLAMP)
that is 5V to 10V greater than VSW(OFF). Use the following
equations to calculate R and C;
(Continued)
step-up regulator, and this requires a larger bypass capacitor
to decouple the LM1577/LM2577 VIN pin from this noise. For
most applications, a low ESR, 1.0 µF cap will be sufficient, if
it is connected very close to the VIN and Ground pins.
Transformer
Input
Type
Voltage
LP = 100 µH
5V
N=1
5V
1
5V
10V
10V
2
LP = 200 µH
10V
N = 0.5
12V
12V
12V
3
LP = 250 µH
15V
N = 0.5
15V
15V
Transformer
Dual
Maximum
Output
Output
Voltage
Current
± 10V
± 12V
± 15V
± 10V
± 12V
± 15V
± 10V
± 12V
± 15V
± 10V
± 12V
± 15V
325 mA
275 mA
Power dissipation (and power rating) of the resistor is;
225 mA
700 mA
575 mA
500 mA
The fast recovery diode must have a reverse voltage rating
greater than VCLAMP.
800 mA
700 mA
575 mA
900 mA
825 mA
700 mA
Manufacturers’ Part Numbers
Type
AIE
Pulse
Renco
1
326-0637
PE-65300
RL-2580
2
330-0202
PE-65301
RL-2581
3
330-0203
PE-65302
RL-2582
FIGURE 20. Flyback Transformer Selection Guide
In addition to this bypass cap, a larger capacitor (≥ 47 µF)
should be used where the flyback transformer connects to
the input supply. This will attenuate noise which may interfere with other circuits connected to the same input supply
voltage.
01146819
FIGURE 21. Snubber Circuit
FLYBACK REGULATOR CIRCUIT EXAMPLE
The circuit of Figure 22 produces ± 15V (at 225 mA each)
from a single 5V input. The output regulation of this circuit is
shown in Figure 23 and Figure 25, while the load transient
response is shown in Figure 24 and Figure 26. Switching
waveforms seen in this circuit are shown in Figure 27.
6. Snubber Circuit
A “snubber” circuit is required when operating from input
voltages greater than 10V, or when using a transformer with
LP ≥ 200 µH. This circuit clamps a voltage spike from the
transformer primary that occurs immediately after the output
switch turns off. Without it, the switch voltage may exceed
the 65V maximum rating. As shown in Figure 21, the snub-
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24
LM1577/LM2577
Application Hints
(Continued)
01146820
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 22. Flyback Regulator Easily Provides Dual Outputs
01146823
A: Output Voltage Change, 100 mV/div
B: Output Current, 100 mA/div
01146821
Horizontal: 10 ms/div
FIGURE 23. Line Regulation (Typical) of Flyback
Regulator of Figure 22, +15V Output
FIGURE 24. Load Transient Response of Flyback
Regulator of Figure 22, +15V Output
25
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LM1577/LM2577
Application Hints
(Continued)
01146824
A: Output Voltage Change, 100 mV/div
B: Output Current, 100 mA/div
Horizontal: 10 ms/div
FIGURE 26. Load Transient Response of Flyback
Regulator of Figure 22, −15V Output
01146822
FIGURE 25. Line Regulation (Typical) of Flyback
Regulator of Figure 22, −15V Output
01146825
A: Switch pin voltage, 20 V/div
B: Primary current, 2 A/div
C: +15V Secondary current, 1 A/div
D: +15V Output ripple voltage, 100 mV/div
Horizontal: 5 µs/div
FIGURE 27. Switching Waveforms of Flyback Regulator of Figure 22, Each Output Loaded with 60Ω
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26
LM1577/LM2577
Physical Dimensions
inches (millimeters)
unless otherwise noted
TO-3 Metal Can Package (K)
Order Number LM1577K-12/883, LM1577K-15/883, or LM1577K-ADJ/883
NS Package Number K04A
0.300 Wide SO Package (M)
Order Number LM2577M-12, LM2577M-15 or LM2577M-ADJ
NS Package Number M24B
27
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LM1577/LM2577
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
Order Number LM2577N-12, LM2577N-15, or LM2577N-ADJ
NS Package Number N16A
TO-220, Straight Leads (T)
Order Number LM2577T-12, LM2577T-15, or LM2577T-ADJ
NS Package Number TO5A
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28
LM1577/LM2577
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
TO-220, Bent Staggered Leads (T)
Order Number LM2577T-12 Flow LB03, LM2577T-15 Flow LB03, or LM2577T-ADJ Flow LB03
NS Package Number T05D
29
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LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
5-Lead TO-263 (S)
Order Number LM2577S-12, LM2577S-15 or LM2577S-ADJ
NS Package Number TS5B
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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LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
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