LM2577S-12/NOPB National Semiconductor, LM2577S-12/NOPB Datasheet - Page 18
![IC REG SIMPLE SWITCHER TO-263-5](/photos/7/0/70012/ts5b_sml.jpg)
LM2577S-12/NOPB
Manufacturer Part Number
LM2577S-12/NOPB
Description
IC REG SIMPLE SWITCHER TO-263-5
Manufacturer
National Semiconductor
Series
SIMPLE SWITCHER®r
Type
Step-Up (Boost), Flyback, Forward Converterr
Datasheet
1.LM2577T-15NOPB.pdf
(31 pages)
Specifications of LM2577S-12/NOPB
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
12V
Current - Output
3A
Frequency - Switching
52kHz
Voltage - Input
3.5 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (5 leads + tab)
Input Voltage
40V
Output Voltage
15V
No. Of Pins
5
Operating Temperature Range
-40°C To +125°C
Msl
MSL 3 - 168 Hours
Switching Frequency Max
52kHz
Termination Type
SMD
Voltage Regulator Type
Boost Switching
Rohs Compliant
Yes
Filter Terminals
SMD
Input Voltage Primary Max
40V
Output Current Max
3A
For Use With
551011367-061 - BOARD WEBENCH LM2577,LM2585/87
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Other names
*LM2577S-12
*LM2577S-12/NOPB
LM2577S-12
*LM2577S-12/NOPB
LM2577S-12
www.national.com
Application Hints
2. Compensation Network (R
(C
R
stabilizes the regulator. The values of R
dependant on the regulator voltage gain, I
C
and C
procedure doesn’t necessarily result in R
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
sient response when pulsing I
A. First, calculate the maximum value for R
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
two equations.
The larger of these two values is the minimum value that
ensures stability.
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
C
OUT
OUT
Inductor
FIGURE 10. Table of Standardized Inductors and
and C
H1000
H1500
H2200
Code
H150
H220
H330
H470
H680
L100
L150
L220
L330
L470
L680
. The following procedure calculates values for R
L47
L68
) Selection
OUT
C
that ensure regulator stability. Be aware that this
form a pole-zero compensation network that
Manufacturer’s Part Numbers
67126980
67126990
67127000
67127010
67127020
67127030
67127040
67127050
67127060
67127070
67127080
67127090
67127100
67127120
67127130
67127110
Schott
Manufacturer’s Part Number
LOAD
C
(Continued)
, C
PE - 53112
PE - 92114
PE - 92108
PE - 53113
PE - 52626
PE - 52627
PE - 53114
PE - 52629
PE - 53115
PE - 53116
PE - 53117
PE - 53118
PE - 53119
PE - 53120
PE - 53121
PE - 53122
C
Pulse
) and Output Capacitor
(see Figure 15).
OUT
C
C
using the following
and C
LOAD(max)
and C
C
.
C
RL2442
RL2443
RL2444
RL1954
RL1953
RL1952
RL1951
RL1950
RL2445
RL2446
RL2447
RL1961
RL1960
RL1959
RL1958
RL2448
C
are mainly
Renco
OUT
that pro-
, L and
C
, C
tran-
C
,
18
C. Calculate the minimum value of 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
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
the preceding calculations for C
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.
C
and C
C
needed to stabilize the regulator. As a result,
C
≥ 0.22 µF.
C
and R
C
.
C
are only valid if