LM1577,LM2577
LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
Literature Number: SNOS658C
LM1577/LM2577
SIMPLE SWITCHER®Step-Up Voltage Regulator
General Description
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 regula-
tors.
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 compo-
nents, 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.
Features
nRequires few external components
nNPN output switches 3.0A, can stand off 65V
nWide input voltage range: 3.5V to 40V
nCurrent-mode operation for improved transient
response, line regulation, and current limit
n52 kHz internal oscillator
nSoft-start function reduces in-rush current during start-up
nOutput switch protected by current limit, under-voltage
lockout, and thermal shutdown
Typical Applications
nSimple boost regulator
nFlyback and forward regulators
nMultiple-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.
April 2005
LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
© 2005 National Semiconductor Corporation DS011468 www.national.com
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
01146832
Top View
01146833
Side View
Order Number LM2577S-12, LM2577S-15,
or LM2577S-ADJ
See NS Package Number TS5B
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
LM1577/LM2577
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Ordering Information
Temperature
Range
Package
Type
Output Voltage NSC
12V 15V ADJ Package Package
Drawing
−40˚C ≤T
A
≤+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
Leads Flow LB03 Flow LB03 Flow LB03
−55˚C ≤T
A
≤+150˚C 4-Pin TO-3 LM1577K-12/883LM1577K-15/883 LM1577K-
ADJ/883
K04A TO-3
Typical Application
01146801
Note: Pin numbers shown are for TO-220 (T) package.
LM1577/LM2577
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage 45V
Output Switch Voltage 65V
Output Switch Current (Note 2) 6.0A
Power Dissipation Internally Limited
Storage Temperature Range −65˚C to +150˚C
Lead Temperature
(Soldering, 10 sec.) 260˚C
Maximum Junction Temperature 150˚C
Minimum ESD Rating
(C = 100 pF, R = 1.5 kΩ)2kV
Operating Ratings
Supply Voltage 3.5V ≤V
IN
≤40V
Output Switch Voltage 0V ≤V
SWITCH
≤60V
Output Switch Current I
SWITCH
≤3.0A
Junction Temperature Range
LM1577 −55˚C ≤T
J
≤+150˚C
LM2577 −40˚C ≤T
J
≤+125˚C
Electrical Characteristics—LM1577-12, LM2577-12
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, and I
SWITCH
=0.
LM1577-12 LM2577-12 Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
SYSTEM PARAMETERS Circuit of Figure 1 (Note 6)
V
OUT
Output Voltage V
IN
= 5V to 10V 12.0 V
I
LOAD
= 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)
Line Regulation V
IN
= 3.5V to 10V 20 mV
I
LOAD
= 300 mA 50/100 50/100 mV(max)
Load Regulation V
IN
=5V 20 mV
I
LOAD
= 100 mA to 800 mA 50/100 50/100 mV(max)
ηEfficiency V
IN
= 5V, I
LOAD
= 800 mA 80 %
DEVICE PARAMETERS
I
S
Input Supply Current V
FEEDBACK
= 14V (Switch Off) 7.5 mA
10.0/14.0 10.0/14.0 mA(max)
I
SWITCH
= 2.0A 25 mA
V
COMP
= 2.0V (Max Duty Cycle) 50/85 50/85 mA(max)
V
UV
Input Supply I
SWITCH
= 100 mA 2.90 V
Undervoltage Lockout 2.70/2.65 2.70/2.65 V(min)
3.10/3.15 3.10/3.15 V(max)
f
O
Oscillator Frequency Measured at Switch Pin 52 kHz
I
SWITCH
= 100 mA 48/42 48/42 kHz(min)
56/62 56/62 kHz(max)
V
REF
Output Reference Measured at Feedback Pin V
Voltage V
IN
= 3.5V to 40V 12 11.76/11.64 11.76/11.64 V(min)
V
COMP
= 1.0V 12.24/12.36 12.24/12.36 V(max)
Output Reference V
IN
= 3.5V to 40V 7mV
Voltage Line Regulator
R
FB
Feedback Pin Input 9.7 kΩ
Resistance
G
M
Error Amp I
COMP
= −30 µA to +30 µA 370 µmho
Transconductance V
COMP
= 1.0V 225/145 225/145 µmho(min)
515/615 515/615 µmho(max)
LM1577/LM2577
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Electrical Characteristics—LM1577-12, LM2577-12 (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, and I
SWITCH
=0.
LM1577-12 LM2577-12 Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
DEVICE PARAMETERS
A
VOL
Error Amp V
COMP
= 1.1V to 1.9V 80 V/V
Voltage Gain R
COMP
= 1.0 MΩ50/25 50/25 V/V(min)
(Note 7)
Error Amplifier Upper Limit 2.4 V
Output Swing V
FEEDBACK
= 10.0V 2.2/2.0 2.2/2.0 V(min)
Lower Limit 0.3 V
V
FEEDBACK
= 15.0V 0.40/0.55 0.40/0.55 V(max)
Error Amplifier V
FEEDBACK
= 10.0V to 15.0V ±200 µA
Output Current V
COMP
= 1.0V ±130/±90 ±130/±90 µA(min)
±300/±400 ±300/±400 µA(max)
I
SS
Soft Start Current V
FEEDBACK
= 10.0V 5.0 µA
V
COMP
= 0V 2.5/1.5 2.5/1.5 µA(min)
7.5/9.5 7.5/9.5 µA(max)
D Maximum Duty Cycle V
COMP
= 1.5V 95 %
I
SWITCH
= 100 mA 93/90 93/90 %(min)
Switch
Transconductance
12.5 A/V
I
L
Switch Leakage V
SWITCH
= 65V 10 µA
Current V
FEEDBACK
= 15V (Switch Off) 300/600 300/600 µA(max)
V
SAT
Switch Saturation I
SWITCH
= 2.0A 0.5 V
Voltage V
COMP
= 2.0V (Max Duty Cycle) 0.7/0.9 0.7/0.9 V(max)
NPN Switch 4.5 A
Current Limit 3.7/3.0 3.7/3.0 A(min)
5.3/6.0 5.3/6.0 A(max)
Electrical Characteristics—LM1577-15, LM2577-15
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, and I
SWITCH
=0.
LM1577-15 LM2577-15 Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
SYSTEM PARAMETERS Circuit of Figure 2 (Note 6)
V
OUT
Output Voltage V
IN
= 5V to 12V 15.0 V
I
LOAD
= 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)
Line Regulation V
IN
= 3.5V to 12V 20
50/100 50/100
mV
I
LOAD
= 300 mA mV(max)
Load Regulation V
IN
=5V 20
50/100 50/100
mV
I
LOAD
= 100 mA to 600 mA mV(max)
ηEfficiency V
IN
= 5V, I
LOAD
= 600 mA 80 %
LM1577/LM2577
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Electrical Characteristics—LM1577-15, LM2577-15 (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, and I
SWITCH
=0.
LM1577-15 LM2577-15 Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
DEVICE PARAMETERS
I
S
Input Supply Current V
FEEDBACK
= 18.0V 7.5 mA
(Switch Off) 10.0/14.0 10.0/14.0 mA(max)
I
SWITCH
= 2.0A 25 mA
V
COMP
= 2.0V 50/85 50/85 mA(max)
(Max Duty Cycle)
V
UV
Input Supply I
SWITCH
= 100 mA 2.90 V
Undervoltage 2.70/2.65 2.70/2.65 V(min)
Lockout 3.10/3.15 3.10/3.15 V(max)
f
O
Oscillator Frequency Measured at Switch Pin 52 kHz
I
SWITCH
= 100 mA 48/42 48/42 kHz(min)
56/62 56/62 kHz(max)
V
REF
Output Reference Measured at Feedback Pin V
Voltage V
IN
= 3.5V to 40V 15 14.70/14.55 14.70/14.55 V(min)
V
COMP
= 1.0V 15.30/15.45 15.30/15.45 V(max)
Output Reference V
IN
= 3.5V to 40V 10 mV
Voltage Line Regulation
R
FB
Feedback Pin Input 12.2 kΩ
Voltage Line Regulator
G
M
Error Amp I
COMP
= −30 µA to +30 µA 300 µmho
Transconductance V
COMP
= 1.0V 170/110 170/110 µmho(min)
420/500 420/500 µmho(max)
A
VOL
Error Amp V
COMP
= 1.1V to 1.9V 65 V/V
Voltage Gain R
COMP
= 1.0 MΩ40/20 40/20 V/V(min)
(Note 7)
Error Amplifier Upper Limit 2.4 V
Output Swing V
FEEDBACK
= 12.0V 2.2/2.0 2.2/2.0 V(min)
Lower Limit 0.3 V
V
FEEDBACK
= 18.0V 0.4/0.55 0.40/0.55 V(max)
Error Amp V
FEEDBACK
= 12.0V to 18.0V ±200 µA
Output Current V
COMP
= 1.0V ±130/±90 ±130/±90 µA(min)
±300/±400 ±300/±400 µA(max)
I
SS
Soft Start Current V
FEEDBACK
= 12.0V 5.0 µA
V
COMP
= 0V 2.5/1.5 2.5/1.5 µA(min)
7.5/9.5 7.5/9.5 µA(max)
D Maximum Duty V
COMP
= 1.5V 95 %
Cycle I
SWITCH
= 100 mA 93/90 93/90 %(min)
Switch
Transconductance
12.5 A/V
I
L
Switch Leakage V
SWITCH
= 65V 10 µA
Current V
FEEDBACK
= 18.0V 300/600 300/600 µA(max)
(Switch Off)
V
SAT
Switch Saturation I
SWITCH
= 2.0A 0.5 V
Voltage V
COMP
= 2.0V 0.7/0.9 0.7/0.9 V(max)
(Max Duty Cycle)
LM1577/LM2577
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Electrical Characteristics—LM1577-15, LM2577-15 (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, and I
SWITCH
=0.
LM1577-15 LM2577-15 Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
DEVICE PARAMETERS
NPN Switch V
COMP
= 2.0V 4.3 A
Current Limit 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 T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, V
FEEDBACK
=V
REF
, and I
SWITCH
=0.
LM1577-ADJ LM2577-ADJ Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
SYSTEM PARAMETERS Circuit of Figure 3 (Note 6)
V
OUT
Output Voltage V
IN
= 5V to 10V 12.0 V
I
LOAD
= 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)
∆V
OUT
/ Line Regulation V
IN
= 3.5V to 10V 20 mV
∆V
IN
I
LOAD
= 300 mA 50/100 50/100 mV(max)
∆V
OUT
/ Load Regulation V
IN
=5V 20 mV
∆I
LOAD
I
LOAD
= 100 mA to 800 mA 50/100 50/100 mV(max)
ηEfficiency V
IN
= 5V, I
LOAD
= 800 mA 80 %
DEVICE PARAMETERS
I
S
Input Supply Current V
FEEDBACK
= 1.5V (Switch Off) 7.5 mA
10.0/14.0 10.0/14.0 mA(max)
I
SWITCH
= 2.0A 25 mA
V
COMP
= 2.0V (Max Duty Cycle) 50/85 50/85 mA(max)
V
UV
Input Supply I
SWITCH
= 100 mA 2.90 V
Undervoltage Lockout 2.70/2.65 2.70/2.65 V(min)
3.10/3.15 3.10/3.15 V(max)
f
O
Oscillator Frequency Measured at Switch Pin 52 kHz
I
SWITCH
= 100 mA 48/42 48/42 kHz(min)
56/62 56/62 kHz(max)
V
REF
Reference Measured at Feedback Pin V
Voltage V
IN
= 3.5V to 40V 1.230 1.214/1.206 1.214/1.206 V(min)
V
COMP
= 1.0V 1.246/1.254 1.246/1.254 V(max)
∆V
REF
/ Reference Voltage V
IN
= 3.5V to 40V 0.5 mV
∆V
IN
Line Regulation
I
B
Error Amp V
COMP
= 1.0V 100 nA
Input Bias Current 300/800 300/800 nA(max)
G
M
Error Amp I
COMP
= −30 µA to +30 µA 3700 µmho
Transconductance V
COMP
= 1.0V 2400/1600 2400/1600 µmho(min)
4800/5800 4800/5800 µmho(max)
A
VOL
Error Amp V
COMP
= 1.1V to 1.9V 800 V/V
Voltage Gain R
COMP
= 1.0 MΩ(Note 7) 500/250 500/250 V/V(min)
LM1577/LM2577
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Electrical Characteristics—LM1577-ADJ, LM2577-ADJ (Continued)
Specifications with standard type face are for T
J
= 25˚C, and those in bold type face apply over full Operating Temperature
Range. Unless otherwise specified, V
IN
= 5V, V
FEEDBACK
=V
REF
, and I
SWITCH
=0.
LM1577-ADJ LM2577-ADJ Units
Symbol Parameter Conditions Typical Limit Limit (Limits)
(Notes 3, 4) (Note 5)
DEVICE PARAMETERS
Error Amplifier Upper Limit 2.4 V
Output Swing V
FEEDBACK
= 1.0V 2.2/2.0 2.2/2.0 V(min)
Lower Limit 0.3 V
V
FEEDBACK
= 1.5V 0.40/0.55 0.40/0.55 V(max)
Error Amp V
FEEDBACK
= 1.0V to 1.5V ±200 µA
Output Current V
COMP
= 1.0V ±130/±90 ±130/±90 µA(min)
±300/±400 ±300/±400 µA(max)
I
SS
Soft Start Current V
FEEDBACK
= 1.0V 5.0 µA
V
COMP
= 0V 2.5/1.5 2.5/1.5 µA(min)
7.5/9.5 7.5/9.5 µA(max)
D Maximum Duty Cycle V
COMP
= 1.5V 95 %
I
SWITCH
= 100 mA 93/90 93/90 %(min)
∆I
SWITCH
/ Switch 12.5 A/V
∆V
COMP
Transconductance
I
L
Switch Leakage V
SWITCH
= 65V 10 µA
Current V
FEEDBACK
= 1.5V (Switch Off) 300/600 300/600 µA(max)
V
SAT
Switch Saturation I
SWITCH
= 2.0A 0.5 V
Voltage V
COMP
= 2.0V (Max Duty Cycle) 0.7/0.9 0.7/0.9 V(max)
NPN Switch V
COMP
= 2.0V 4.3 A
Current Limit 3.7/3.0 3.7/3.0 A(min)
5.3/6.0 5.3/6.0 A(max)
THERMAL PARAMETERS (All Versions)
θ
JA
Thermal Resistance K Package, Junction to Ambient 35
˚C/W
θ
JC
K Package, Junction to Case 1.5
θ
JA
T Package, Junction to Ambient 65
θ
JC
T Package, Junction to Case 2
θ
JA
N Package, Junction to 85
Ambient (Note 8)
θ
JA
M Package, Junction 100
to Ambient (Note 8)
θ
JA
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 MΩresistor 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.
LM1577/LM2577
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Electrical Characteristics—LM1577-ADJ, LM2577-ADJ (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 Temperature
∆Reference Voltage
vs Supply Voltage
01146836 01146837
∆Reference Voltage
vs Supply Voltage
∆Reference Voltage
vs Supply Voltage
01146838 01146839
LM1577/LM2577
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Typical Performance Characteristics (Continued)
Error Amp Transconductance
vs Temperature
Error Amp Transconductance
vs Temperature
01146840 01146841
Error Amp Transconductance
vs Temperature
Error Amp Voltage
Gain vs Temperature
01146842 01146843
Error Amp Voltage
Gain vs Temperature
Error Amp Voltage
Gain vs Temperature
01146844 01146845
LM1577/LM2577
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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
01146848 01146849
Switch Saturation Voltage
vs Switch Current
Switch Transconductance
vs Temperature
01146850 01146851
LM1577/LM2577
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LM1577-12, LM2577-12 Test Circuit
LM1577-15, LM2577-15 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
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
LM1577/LM2577
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LM1577-ADJ, LM2577-ADJ Test Circuit
Application Hints
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
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
LM1577/LM2577
www.national.com 14
Application Hints (Continued)
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.
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 V
IN
/L, storing current in the inductor.
When the switch turns off, the lower end of the inductor flies
above V
IN
, discharging its current through diode (D) into the
output capacitor (C
OUT
) at a rate of (V
OUT
−V
IN
)/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 trans-
ferred 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 ref-
erence. The error amp output voltage is compared to a
voltage proportional to the switch current (i.e., inductor cur-
rent during the switch on time).
The comparator terminates the switch on time when the two
voltages are equal, thereby controlling the peak switch cur-
rent to maintain a constant output voltage.
Voltage and current waveforms for this circuit are shown in
Figure 5, and formulas for calculating them are given in
Figure 6.
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:
V
IN (min)
= Minimum input supply voltage
V
OUT
= Regulated output voltage
I
LOAD(max)
= Maximum output load current
Before proceeding any further, determine if the LM1577/
LM2577 can provide these values of V
OUT
and I
LOAD(max)
when operating with the minimum value of V
IN
. The upper
limits for V
OUT
and I
LOAD(max)
are given by the following
equations.
V
OUT
≤60V
and V
OUT
≤10xV
IN(min)
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 I
LOAD (max)
. The shaded region indicates con-
01146811
FIGURE 5. Step-Up Regulator Waveforms
Duty Cycle D
Average
Inductor
Current
I
IND(AVE)
Inductor
Current Ripple ∆I
IND
Peak Inductor
Current I
IND(PK)
Peak Switch
Current I
SW(PK)
Switch
Voltage When
Off
V
SW(OFF)
V
OUT
+V
F
Diode
Reverse
Voltage
V
R
V
OUT
−V
SAT
Average
Diode Current I
D(AVE)
I
LOAD
Peak Diode
Current I
D(PK)
Power
Dissipation of
LM1577/2577
P
D
VF= Forward Biased Diode Voltage
ILOAD = Output Load Current
FIGURE 6. Step-Up Regulator Formulas
LM1577/LM2577
www.national.com15
Application Hints (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 V
F
= 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:
I
IND,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 I
IND,DC
.
This code gives the inductor value in microhenries. The
L or H prefix signifies whether the inductor is rated for a
maximum E•Tof90V
•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:
If L
MIN
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:
1. Find the lowest value inductor that is greater than L
MIN
.
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.
01146827
FIGURE 7. LM2577-12 Inductor Selection Guide
01146828
FIGURE 8. LM2577-15 Inductor Selection Guide
LM1577/LM2577
www.national.com 16
Application Hints (Continued)
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 gener-
ate more EMI than the other types, and this may interfere
with signals sensitive to noise.
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
LM1577/LM2577
www.national.com17
Application Hints (Continued)
2. Compensation Network (R
C
,C
C
) and Output Capacitor
(C
OUT
) Selection
R
C
and C
C
form a pole-zero compensation network that
stabilizes the regulator. The values of R
C
and C
C
are mainly
dependant on the regulator voltage gain, I
LOAD(max)
, L and
C
OUT
. The following procedure calculates values for R
C
,C
C
,
and C
OUT
that ensure regulator stability. Be aware that this
procedure doesn’t necessarily result in R
C
and C
C
that pro-
vide optimum compensation. In order to guarantee optimum
compensation, one of the standard procedures for testing
loop stability must be used, such as measuring V
OUT
tran-
sient response when pulsing I
LOAD
(see Figure 15).
A. First, calculate the maximum value for R
C
.
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 C
OUT
using the following
two equations.
The larger of these two values is the minimum value that
ensures stability.
C. Calculate the minimum value of C
C
.
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 imme-
diately rise to 90%, drawing huge currents from the input
power supply). In order to operate properly, the soft start
circuit requires C
C
≥0.22 µF.
The value of the output filter capacitor is normally large
enough to require the use of aluminum electrolytic capaci-
tors. Figure 11 lists several different types that are recom-
mended for switching regulators, and the following param-
eters are used to select the proper capacitor.
Working Voltage (WVDC): Choose a capacitor with a work-
ing 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
Choose a capacitor that is rated at least 50% higher than this
value at 52 kHz.
Equivalent Series Resistance (ESR) : This is the primary
cause of output ripple voltage, and it also affects the values
of R
C
and C
C
needed to stabilize the regulator. As a result,
the preceding calculations for C
C
and R
C
are only valid if
ESR doesn’t exceed the maximum value specified by the
following equations.
Select a capacitor with ESR, at 52 kHz, that is less than or
equal to the lower value calculated. Most electrolytic capaci-
tors 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.
Inductor Manufacturer’s Part Number
Code Schott Pulse Renco
L47 67126980 PE - 53112 RL2442
L68 67126990 PE - 92114 RL2443
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
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
FIGURE 10. Table of Standardized Inductors and
Manufacturer’s Part Numbers
LM1577/LM2577
www.national.com 18
Application Hints (Continued)
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.
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
V
OUT
= 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 V
OUT
,
select R1 and R2 so that
4. Input Capacitor Selection (C
IN
)
The switching action in the step-up regulator causes a trian-
gular 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.
If the LM1577 is located far from the supply source filter
capacitors, an additional large electrolytic capacitor (e.g.
47 µF) is often required.
5. Diode Selection (D)
The switching diode used in the boost regulator must with-
stand 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 I
LOAD(max)
and I
D(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.
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.
Cornell Dublier — Types 239, 250, 251, UFT,
300, or 350
P.O. Box 128, Pickens, SC 29671
(803) 878-6311
Nichicon — Types PF, PX, or PZ
927 East Parkway,
Schaumburg, IL 60173
(708) 843-7500
Sprague — Types 672D, 673D, or 674D
Box 1, Sprague Road,
Lansing, NC 28643
(919) 384-2551
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
V
OUT
Schottky Fast Recovery
(max) 1A 3A 1A 3A
20V 1N5817 1N5820
MBR120P MBR320P
1N5818 1N5821
30V MBR130P MBR330P
11DQ03 31DQ03
1N5819 1N5822
40V MBR140P MBR340P
11DQ04 31DQ04
MBR150 MBR350 1N4933
50V 11DQ05 31DQ05 MUR105
1N4934 MR851
100V HER102 30DL1
MUR110 MR831
10DL1 HER302
FIGURE 12. Diode Selection Chart
LM1577/LM2577
www.national.com19
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
01146815
A: Output Voltage Change, 100 mV/div. (AC-coupled)
B: Load current, 0.2 A/div
Horizontal: 5 ms/div
FIGURE 15. Load Transient Response of Step-Up
Regulator of Figure 13
01146816
A: Switch pin voltage, 10 V/div
B: Switch pin current, 2 A/div
C: Inductor current, 2 A/div
D: Output ripple voltage, 100 mV/div (AC-coupled)
Horizontal: 5 µs/div
FIGURE 16. Switching Waveforms of Step-Up
Regulator of Figure 13
LM1577/LM2577
www.national.com 20
Application Hints (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 out-
puts. Its operation is similar to a step-up regulator, except the
output switch contols the primary current of a flyback trans-
former. 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.
Voltage and current waveforms for this circuit are shown in
Figure 17, and formulas for calculating them are given in
Figure 19.
FLYBACK REGULATOR DESIGN PROCEDURE
1. Transformer Selection
A family of standardized flyback transformers is available for
creating flyback regulators that produce dual output volt-
ages, 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 (C
C
,R
C
) and
Output Capacitor (C
OUT
) Selection
As explained in the Step-Up Regulator Design Procedure,
C
C
,R
C
and C
OUT
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 ∑I
LOAD(max)
to I
LOAD(max)
in the following equations.
A. First, calculate the maximum value for R
C
.
Where ∑I
LOAD(max)
is the sum of the load current (magni-
tude) 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 ∑C
OUT
(sum of C
OUT
at both outputs) using the following two equations.
The larger of these two values must be used to ensure
regulator stability.
01146817
FIGURE 17. Flyback Regulator Waveforms
LM1577/LM2577
www.national.com21
Application Hints (Continued)
01146818
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 18. LM1577-ADJ/LM2577-ADJ Flyback Regulator with ±Outputs
LM1577/LM2577
www.national.com 22
Application Hints (Continued)
C. Calculate the minimum value of C
C
D. Calculate the maximum ESR of the +V
OUT
and −V
OUT
output capacitors in parallel.
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 regard-
ing the selection of C
OUT
.
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
V
OUT
= 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 V
OUT
, select
R1 and R2 so that
4. Diode Selection
The switching diode in a flyback converter must withstand
the reverse voltage specified by the following equation.
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
Duty Cycle D
Primary Current Variation
∆I
P
Peak Primary Current
I
P(PK)
Switch Voltage when Off
V
SW(OFF)
Diode Reverse Voltage V
R
V
OUT+
N(V
IN−
V
SAT
)
Average Diode Current I
D(AVE)
I
LOAD
Peak Diode Current
I
D(PK)
Short Circuit Diode Current
Power Dissipation of
LM1577/LM2577
P
D
01146878
FIGURE 19. Flyback Regulator Formulas
LM1577/LM2577
www.national.com23
Application Hints (Continued)
step-up regulator, and this requires a larger bypass capacitor
to decouple the LM1577/LM2577 V
IN
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 V
IN
and Ground pins.
Transformer Input Dual Maximum
Type Voltage Output Output
Voltage Current
L
P
= 100 µH 5V ±10V 325 mA
1 N=1 5V ±12V 275 mA
5V ±15V 225 mA
10V ±10V 700 mA
10V ±12V 575 mA
2L
P
= 200 µH 10V ±15V 500 mA
N = 0.5 12V ±10V 800 mA
12V ±12V 700 mA
12V ±15V 575 mA
3L
P
= 250 µH 15V ±10V 900 mA
N = 0.5 15V ±12V 825 mA
15V ±15V 700 mA
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 inter-
fere with other circuits connected to the same input supply
voltage.
6. Snubber Circuit
A “snubber” circuit is required when operating from input
voltages greater than 10V, or when using a transformer with
L
P
≥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-
ber consists of a fast recovery diode, and a parallel RC. The
RC values are selected for switch clamp voltage (V
CLAMP
)
that is 5V to 10V greater than V
SW(OFF)
. Use the following
equations to calculate R and C;
Power dissipation (and power rating) of the resistor is;
The fast recovery diode must have a reverse voltage rating
greater than V
CLAMP
.
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.
Transformer 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
01146819
FIGURE 21. Snubber Circuit
LM1577/LM2577
www.national.com 24
Application Hints (Continued)
01146820
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 22. Flyback Regulator Easily Provides Dual Outputs
01146821
FIGURE 23. Line Regulation (Typical) of Flyback
Regulator of Figure 22, +15V Output
01146823
A: Output Voltage Change, 100 mV/div
B: Output Current, 100 mA/div
Horizontal: 10 ms/div
FIGURE 24. Load Transient Response of Flyback
Regulator of Figure 22, +15V Output
LM1577/LM2577
www.national.com25
Application Hints (Continued)
01146822
FIGURE 25. Line Regulation (Typical) of Flyback
Regulator of Figure 22, −15V Output
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
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
LM1577/LM2577
www.national.com 26
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
LM1577/LM2577
www.national.com27
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
LM1577/LM2577
www.national.com 28
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
LM1577/LM2577
www.national.com29
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
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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
Tel: 81-3-5639-7560www.national.com
LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator
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