LM2577S-12/NOPB National Semiconductor, LM2577S-12/NOPB Datasheet - Page 18

• 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

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

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., [phone]
1000 Parkers Lake Rd., Wayzata, MN 55391
Pulse Engineering, [phone]
P.O. Box 12235, San Diego, CA 92112
Renco Electronics Inc., [phone]
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