NSC LM2577-12 Simple switcher step-up voltage regulator Datasheet

LM1577/LM2577 Series
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.
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.
n
n
n
n
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
Typical Applications
n Simple boost regulator
n Flyback and forward regulators
n Multiple-output regulator
Typical Application
DS011468-1
Note: Pin numbers shown are for TO-220 (T) package.
Ordering Information
Temperature
Range
Package
Type
Output Voltage
NSC
12V
15V
ADJ
Package Package
24-Pin Surface Mount
LM2577M-12
LM2577M-15
LM2577M-ADJ
M24B
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
Drawing
−40˚C ≤ TA ≤ +125˚C
Leads
−55˚C ≤ TA ≤ +150˚C
4-Pin TO-3
LM1577K-12/883 LM1577K-15/883
LM1577KADJ/883
SO
SIMPLE SWITCHER ® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS011468
www.national.com
LM1577/LM2577 Series SIMPLE SWITCHER Step-Up Voltage Regulator
June 1999
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.
Supply Voltage
Output Switch Voltage
Output Switch Current (Note 2)
Power Dissipation
Storage Temperature Range
Lead Temperature
(Soldering, 10 sec.)
Maximum Junction Temperature
2 kV
Operating Ratings
45V
65V
6.0A
Internally Limited
−65˚C to +150˚C
Supply Voltage
Output Switch Voltage
Output Switch Current
Junction Temperature Range
LM1577
LM2577
3.5V ≤ VIN ≤ 40V
0V ≤ VSWITCH ≤ 60V
ISWITCH ≤ 3.0A
−55˚C ≤ TJ ≤ +150˚C
−40˚C ≤ TJ ≤ +125˚C
260˚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
SYSTEM PARAMETERS Circuit of Figure 1 (Note 6)
VOUT
Output Voltage
VIN = 5V to 10V
ILOAD = 100 mA to 800 mA
Line Regulation
(Note 3)
VIN = 3.5V to 10V
Efficiency
Units
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)
50/100
50/100
mV(max)
50/100
50/100
mV(max)
V
20
VIN = 5V
mV
20
ILOAD = 100 mA to 800 mA
η
LM2577-12
Limit
12.0
ILOAD = 300 mA
Load Regulation
LM1577-12
VIN = 5V, ILOAD = 800 mA
80
VFEEDBACK = 14V (Switch Off)
7.5
mV
%
DEVICE PARAMETERS
IS
VUV
Input Supply Current
Input Supply
ISWITCH = 2.0A
VCOMP = 2.0V (Max Duty Cycle)
ISWITCH = 100 mA
VREF
Oscillator Frequency
Output Reference
Measured at Switch Pin
ISWITCH = 100 mA
10.0/14.0
mA(max)
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)
48/42
48/42
kHz(min)
56/62
56/62
kHz(max)
11.76/11.64
11.76/11.64
V(min)
12.24/12.36
12.24/12.36
V(max)
25
mA
2.90
Undervoltage Lockout
fO
mA
10.0/14.0
V
52
kHz
Voltage
Measured at Feedback Pin
VIN = 3.5V to 40V
12
V
Output Reference
VCOMP = 1.0V
VIN = 3.5V to 40V
7
mV
9.7
kΩ
Voltage Line Regulator
RFB
Feedback Pin Input
Resistance
GM
Error Amp
Transconductance
AVOL
Error Amp
Voltage Gain
ICOMP = −30 µA to +30 µA
VCOMP = 1.0V
370
VCOMP = 1.1V to 1.9V
RCOMP = 1.0 MΩ
80
(Note 7)
www.national.com
2
µmho
225/145
225/145
µmho(min)
515/615
515/615
µmho(max)
50/25
50/25
V/V(min)
V/V
Electrical Characteristics — LM1577-12, LM2577-12
(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)
2.2/2.0
2.2/2.0
V(min)
0.40/0.55
0.40/0.55
V(max)
± 130/ ± 90
± 300/ ± 400
± 130/ ± 90
± 300/ ± 400
µA(min)
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)
DEVICE PARAMETERS
Error Amplifier
Output Swing
Error Amplifier
Output Current
ISS
Soft Start Current
D
Maximum Duty Cycle
Upper Limit
VFEEDBACK = 10.0V
2.4
Lower Limit
0.3
VFEEDBACK = 15.0V
VFEEDBACK = 10.0V to 15.0V
VCOMP = 1.0V
IL
5.0
VCOMP = 1.5V
ISWITCH = 100 mA
95
VSAT
µA
µA
%
12.5
Switch Saturation
VSWITCH = 65V
VFEEDBACK = 15V (Switch Off)
ISWITCH = 2.0A
Voltage
VCOMP = 2.0V (Max Duty Cycle)
Switch Leakage
Current
V
± 200
VFEEDBACK = 10.0V
VCOMP = 0V
Switch
Transconductance
V
NPN Switch
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
4.5
Current Limit
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
SYSTEM PARAMETERS Circuit of Figure 2 (Note 6)
VOUT
Output Voltage
VIN = 5V to 12V
ILOAD = 100 mA to 600 mA
Line Regulation
(Note 3)
VIN = 3.5V to 12V
Typical
Efficiency
Units
Limit
(Limits)
(Notes 3, 4)
(Note 5)
14.50/14.25
14.50/14.25
V(min)
15.50/15.75
15.50/15.75
V(max)
50/100
50/100
50/100
50/100
V
20
VIN = 5V
mV
20
ILOAD = 100 mA to 600 mA
η
LM2577-15
Limit
15.0
ILOAD = 300 mA
Load Regulation
LM1577-15
VIN = 5V, ILOAD = 600 mA
80
VFEEDBACK = 18.0V
7.5
mV(max)
mV
mV(max)
%
DEVICE PARAMETERS
IS
Input Supply Current
(Switch Off)
ISWITCH = 2.0A
Input Supply
10.0/14.0
mA(max)
50/85
50/85
mA(max)
25
VCOMP = 2.0V
VUV
mA
10.0/14.0
(Max Duty Cycle)
ISWITCH = 100 mA
2.90
3
mA
V
www.national.com
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.
LM1577-15
LM2577-15
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
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)
Symbol
Parameter
Conditions
Typical
DEVICE PARAMETERS
fO
VREF
Oscillator Frequency
Output Reference
Measured at Switch Pin
ISWITCH = 100 mA
52
kHz
Voltage
Measured at Feedback Pin
VIN = 3.5V to 40V
15
V
Output Reference
VCOMP = 1.0V
VIN = 3.5V to 40V
10
mV
12.2
kΩ
Voltage Line Regulation
RFB
Feedback Pin Input
Voltage Line Regulator
GM
Error Amp
Transconductance
AVOL
Error Amp
Voltage Gain
ICOMP = −30 µA to +30 µA
VCOMP = 1.0V
300
VCOMP = 1.1V to 1.9V
RCOMP = 1.0 MΩ
65
µmho
170/110
170/110
µmho(min)
420/500
420/500
µmho(max)
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(min)
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)
V/V
(Note 7)
Error Amplifier
Output Swing
Error Amp
Output Current
ISS
D
Soft Start Current
Maximum Duty
Cycle
Upper Limit
VFEEDBACK = 12.0V
2.4
Lower Limit
0.3
VFEEDBACK = 18.0V
VFEEDBACK = 12.0V to 18.0V
VCOMP = 1.0V
IL
Switch Leakage
Current
VSAT
5.0
VCOMP = 1.5V
ISWITCH = 100 mA
95
VSWITCH = 65V
VFEEDBACK = 18.0V
Voltage
µA
%
NPN Switch
(Max Duty Cycle)
VCOMP = 2.0V
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
www.national.com
µA
12.5
(Switch Off)
ISWITCH = 2.0A
VCOMP = 2.0V
Switch Saturation
V
± 200
VFEEDBACK = 12.0V
VCOMP = 0V
Switch
Transconductance
V
4
A
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
SYSTEM PARAMETERS Circuit of Figure 3 (Note 6)
VOUT
Output Voltage
VIN = 5V to 10V
∆VOUT/
Line Regulation
∆VIN
∆VOUT/
Load Regulation
∆ILOAD
η
Efficiency
Limit
(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)
50/100
50/100
mV(max)
50/100
50/100
mV(max)
12.0
ILOAD = 100 mA to 800 mA
(Note 3)
VIN = 3.5V to 10V
ILOAD = 300 mA
80
VFEEDBACK = 1.5V (Switch Off)
7.5
(Limits)
V
20
VIN = 5V
ILOAD = 100 mA to 800 mA
VIN = 5V, ILOAD = 800 mA
Units
Limit
mV
20
mV
%
DEVICE PARAMETERS
IS
VUV
Input Supply Current
Input Supply
ISWITCH = 2.0A
VCOMP = 2.0V (Max Duty Cycle)
ISWITCH = 100 mA
VREF
Oscillator Frequency
∆VREF/
Reference Voltage
VCOMP = 1.0V
VIN = 3.5V to 40V
0.5
∆VIN
Line Regulation
VCOMP = 1.0V
100
Error Amp
Transconductance
AVOL
Error Amp
Voltage Gain
Error Amplifier
Output Swing
Error Amp
Output Current
ISS
D
Soft Start Current
Maximum Duty Cycle
∆ISWITCH/
Switch
∆VCOMP
Transconductance
50/85
mA(max)
2.70/2.65
2.70/2.65
V(min)
3.10/3.15
3.10/3.15
V(max)
48/42
48/42
kHz(min)
56/62
56/62
kHz(max)
1.214/1.206
1.214/1.206
V(min)
1.246/1.254
1.246/1.254
V(max)
mA
V
ICOMP = −30 µA to +30 µA
VCOMP = 1.0V
3700
VCOMP = 1.1V to 1.9V
RCOMP = 1.0 MΩ (Note 7)
800
Upper Limit
VFEEDBACK = 1.0V
2.4
Lower Limit
0.3
VFEEDBACK = 1.5V
VFEEDBACK = 1.0V to 1.5V
VCOMP = 1.0V
mV
nA
300/800
300/800
nA(max)
2400/1600
2400/1600
µmho(min)
4800/5800
4800/5800
µmho(max)
500/250
500/250
V/V(min)
2.2/2.0
2.2/2.0
V(min)
0.40/0.55
0.40/0.55
V(max)
± 130/ ± 90
± 300/ ± 400
± 130/ ± 90
± 300/ ± 400
µA(min)
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)
µmho
V/V
V
V
± 200
VFEEDBACK = 1.0V
VCOMP = 0V
5.0
VCOMP = 1.5V
ISWITCH = 100 mA
95
12.5
5
kHz
V
1.230
Input Bias Current
GM
50/85
52
Voltage
Error Amp
mA(max)
2.90
Measured at Feedback Pin
VIN = 3.5V to 40V
IB
Reference
Measured at Switch Pin
ISWITCH = 100 mA
10.0/14.0
25
Undervoltage Lockout
fO
mA
10.0/14.0
µA
µA
%
A/V
www.national.com
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
Units
Limit
Limit
(Limits)
(Notes 3, 4)
(Note 5)
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)
DEVICE PARAMETERS
Switch Leakage
IL
Current
VSAT
Switch Saturation
Voltage
NPN Switch
VSWITCH = 65V
VFEEDBACK = 1.5V (Switch Off)
ISWITCH = 2.0A
VCOMP = 2.0V (Max Duty Cycle)
VCOMP = 2.0V
10
µA
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.
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.
www.national.com
6
Typical Performance Characteristics
Reference Voltage
vs Temperature
Reference Voltage
vs Temperature
DS011468-34
∆ Reference Voltage
vs Supply Voltage
Reference Voltage
vs Temperature
DS011468-35
∆ Reference Voltage
vs Supply Voltage
DS011468-37
Error Amp Transconductance
vs Temperature
∆ Reference Voltage
vs Supply Voltage
DS011468-38
Error Amp Transconductance
vs Temperature
DS011468-40
DS011468-41
7
DS011468-36
DS011468-39
Error Amp Transconductance
vs Temperature
DS011468-42
www.national.com
Typical Performance Characteristics
Error Amp Voltage
Gain vs Temperature
(Continued)
Error Amp Voltage
Gain vs Temperature
DS011468-43
Quiescent Current
vs Temperature
DS011468-44
Quiescent Current
vs Switch Current
DS011468-46
Current Limit Response
Time vs Overdrive
DS011468-45
Current Limit
vs Temperature
DS011468-47
Switch Saturation Voltage
vs Switch Current
DS011468-49
www.national.com
Error Amp Voltage
Gain vs Temperature
Switch Transconductance
vs Temperature
DS011468-50
8
DS011468-48
DS011468-51
Typical Performance Characteristics
(Continued)
Feedback Pin Bias
Current vs Temperature
Oscillator Frequency
vs Temperature
DS011468-52
DS011468-53
Maximum Power Dissipation
(TO-263) (Note 9)
DS011468-31
Connection Diagrams
Straight Leads
5-Lead TO-220 (T)
Bent, Staggered Leads
5-Lead TO-220 (T)
DS011468-4
DS011468-5
Top View
Order Number LM2577T-12, LM2577T-15,
or LM2577T-ADJ
See NS Package Number T05A
Top View
Order Number LM2577T-12 Flow LB03, LM2577T-15
Flow LB03, or LM2577T-ADJ Flow LB03
See NS Package Number T05D
9
www.national.com
Connection Diagrams
(Continued)
16-Lead DIP (N)
24-Lead Surface Mount (M)
DS011468-6
*No internal Connection
Top View
Order Number LM2577N-12, LM2577N-15,
or LM2577N-ADJ
See NS Package Number N16A
DS011468-7
*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
4-Lead TO-3 (K)
DS011468-32
Top View
DS011468-8
Bottom View
Order Number LM1577K-12/883, LM1577K-15/883,
or LM1577K-ADJ/883
See NS Package Number K04A
DS011468-33
Side View
Order Number LM2577S-12, LM2577S-15,
or LM2577S-ADJ
See NS Package Number TS5B
www.national.com
10
LM1577-12, LM2577-12 Test Circuit
DS011468-30
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
DS011468-26
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-ADJ, LM2577-ADJ Test Circuit
DS011468-9
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
11
www.national.com
Application Hints
DS011468-10
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
www.national.com
12
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.
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).
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.
Voltage and current waveforms for this circuit are shown in
Figure 5, and formulas for calculating them are given in Figure 6.
D
Average
Inductor
Current
IIND(AVE)
Inductor
Current
Ripple
∆IIND
Peak
Inductor
Current
IIND(PK)
Peak Switch
Current
ISW(PK)
Switch
Voltage
When Off
VSW(OFF)
VOUT + VF
Diode
Reverse
Voltage
VR
VOUT − VSAT
Average
Diode
Current
ID(AVE)
ILOAD
Peak Diode
Current
ID(PK)
Power
Dissipation
of
LM1577/2577
PD
VF = Forward Biased Diode Voltage
ILOAD = Output Load Current
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
DS011468-11
FIGURE 5. Step-Up Regulator Waveforms
and
VOUT ≤ 10 x VIN(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
13
www.national.com
Application Hints
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:
1. Find the lowest value inductor that is greater than LMIN.
(Continued)
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
conditions 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. 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.
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:
DS011468-27
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:
DS011468-28
FIGURE 8. LM2577-15 Inductor Selection Guide
www.national.com
14
Application Hints
(Continued)
DS011468-12
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.
15
www.national.com
Application Hints
Inductor
(Continued)
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
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.
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.
FIGURE 10. Table of Standardized Inductors and
Manufacturer’s Part Numbers
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.
C. Calculate the minimum value of CC .
www.national.com
16
Application Hints
(Continued)
3. Output Voltage Selection (R1 and R2)
VOUT
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.
(max)
1A
3A
20V
1N5817
1N5820
MBR120P
MBR320P
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
VOUT = 1.23V (1 + R1/R2)
30V
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
40V
50V
Schottky
Fast Recovery
1N5818
1N5821
MBR130P
MBR330P
11DQ03
31DQ03
1N5819
1N5822
MBR140P
MBR340P
1A
11DQ04
31DQ04
MBR150
MBR350
1N4933
11DQ05
31DQ05
MUR105
1N4934
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.
100V
3A
MR851
HER102
30DL1
MUR110
MR831
10DL1
HER302
FIGURE 12. Diode Selection Chart
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
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 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.
17
www.national.com
Application Hints
(Continued)
DS011468-13
Note: Pin numbers shown are for TO-220 (T) package.
FIGURE 13. Step-up Regulator Delivers 12V from a 5V Input
DS011468-14
FIGURE 14. Line Regulation (Typical) of Step-Up Regulator of Figure 13
DS011468-16
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
DS011468-15
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
www.national.com
FIGURE 16. Switching Waveforms of Step-Up
Regulator of Figure 13
18
Application Hints
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.
The larger of these two values must be used to ensure regulator stability.
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 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.
DS011468-17
FIGURE 17. Flyback Regulator Waveforms
DS011468-18
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 18. LM1577-ADJ/LM2577-ADJ Flyback Regulator with ± Outputs
19
www.national.com
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
DS011468-78
FIGURE 19. Flyback Regulator Formulas
C. Calculate the minimum value of CC
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
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.
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
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.
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
VOUT = 1.23V (1 + R1/R2)
www.national.com
20
Application Hints
1
Transformer
Input
Type
Voltage
LP = 100 µH
N=1
5V
5V
5V
10V
10V
2
LP = 200 µH
N = 0.5
10V
12V
12V
12V
3
LP = 250 µH
N = 0.5
15V
15V
15V
Transformer
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)
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.
6. Snubber Circuit
DS011468-19
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.
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 snubber consists of a fast recovery diode, and a parallel RC. The
21
www.national.com
Application Hints
(Continued)
DS011468-20
T1 = Pulse Engineering, PE-65300
D1, D2 = 1N5821
FIGURE 22. Flyback Regulator Easily Provides Dual Outputs
DS011468-21
DS011468-22
FIGURE 23. Line Regulation (Typical) of Flyback
Regulator of Figure 22, +15V Output
FIGURE 25. Line Regulation (Typical) of Flyback
Regulator of Figure 22, −15V Output
DS011468-24
A: Output Voltage Change, 100 mV/div
B: Output Current, 100 mA/div
Horizontal: 10 ms/div
DS011468-23
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
FIGURE 24. Load Transient Response of Flyback
Regulator of Figure 22, +15V Output
www.national.com
22
Application Hints
(Continued)
DS011468-25
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
23
www.national.com
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
www.national.com
24
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
25
www.national.com
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
www.national.com
26
LM1577/LM2577 Series 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
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: [email protected]
www.national.com
National Semiconductor
Europe
Fax: +49 (0) 1 80-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
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.
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: [email protected]
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
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.
Similar pages