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PDF LM2576 Data sheet ( Hoja de datos )
| Número de pieza | LM2576 | |
| Descripción | SIMPLE SWITCHER 3A Step-Down Voltage Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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August 2004
LM2576/LM2576HV Series
SIMPLE SWITCHER® 3A Step-Down Voltage Regulator
General Description
The LM2576 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving 3A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5V, 12V, 15V, and an
adjustable output version.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation and a fixed-frequency oscillator.
The LM2576 series offers a high-efficiency replacement for
popular three-terminal linear regulators. It substantially re-
duces the size of the heat sink, and in some cases no heat
sink is required.
A standard series of inductors optimized for use with the
LM2576 are available from several different manufacturers.
This feature greatly simplifies the design of switch-mode
power supplies.
Other features include a guaranteed ±4% tolerance on out-
put voltage within specified input voltages and output load
conditions, and ±10% on the oscillator frequency. External
shutdown is included, featuring 50 µA (typical) standby cur-
rent. The output switch includes cycle-by-cycle current limit-
ing, as well as thermal shutdown for full protection under
fault conditions.
Features
n 3.3V, 5V, 12V, 15V, and adjustable output versions
n Adjustable version output voltage range,
1.23V to 37V (57V for HV version) ±4% max over
line and load conditions
n Guaranteed 3A output current
n Wide input voltage range, 40V up to 60V for
HV version
n Requires only 4 external components
n 52 kHz fixed frequency internal oscillator
n TTL shutdown capability, low power standby mode
n High efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
n P+ Product Enhancement tested
Applications
n Simple high-efficiency step-down (buck) regulator
n Efficient pre-regulator for linear regulators
n On-card switching regulators
n Positive to negative converter (Buck-Boost)
Typical Application (Fixed Output Voltage
Versions)
FIGURE 1.
01147601
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation DS011476
www.national.com
1 page  
LM2576-ADJ, LM2576HV-ADJ
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature
Range.
Symbol
Parameter
Conditions
LM2576-ADJ
LM2576HV-ADJ
Units
(Limits)
Typ Limit
(Note 2)
SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2
VOUT
Feedback Voltage
VIN = 12V, ILOAD = 0.5A
VOUT = 5V,
Circuit of Figure 2
1.230
1.217
1.243
V
V(Min)
V(Max)
VOUT
VOUT
η
Feedback Voltage
LM2576
Feedback Voltage
LM2576HV
Efficiency
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 40V
VOUT = 5V, Circuit of Figure 2
0.5A ≤ ILOAD ≤ 3A,
8V ≤ VIN ≤ 60V
VOUT = 5V, Circuit of Figure 2
VIN = 12V, ILOAD = 3A, VOUT = 5V
1.230
1.230
77
1.193/1.180
1.267/1.280
1.193/1.180
1.273/1.286
V
V(Min)
V(Max)
V
V(Min)
V(Max)
%
All Output Voltage Versions
Electrical Characteristics
Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature
Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version, VIN = 25V for the 12V version, and VIN
= 30V for the 15V version. ILOAD = 500 mA.
Symbol
Parameter
Conditions
LM2576-XX
Units
LM2576HV-XX
(Limits)
Typ Limit
(Note 2)
DEVICE PARAMETERS
Ib
Feedback Bias Current
VOUT = 5V (Adjustable Version Only)
fO Oscillator Frequency (Note 11)
50 100/500 nA
52 kHz
47/42
kHz
(Min)
58/63
kHz
(Max)
VSAT
Saturation Voltage
IOUT = 3A (Note 4)
1.4 V
1.8/2.0
V(Max)
DC Max Duty Cycle (ON)
(Note 5)
98 %
93 %(Min)
ICL Current Limit
(Notes 4, 11)
5.8 A
4.2/3.5
A(Min)
6.9/7.5
A(Max)
IL
Output Leakage Current
(Notes 6, 7): Output = 0V
2 mA(Max)
Output = −1V 7.5
mA
Output = −1V
30 mA(Max)
IQ Quiescent Current
(Note 6)
5 mA
10 mA(Max)
ISTBY
Standby Quiescent
Current
ON /OFF Pin = 5V (OFF)
50 µA
200 µA(Max)
5 www.national.com
5 Page 
LM2576 Series Buck Regulator
Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
Given: VOUT = Regulated Output Voltage (3.3V, 5V, 12V,
or 15V) VIN(Max) = Maximum Input Voltage ILOAD(Max) =
Maximum Load Current
1. Inductor Selection (L1) A. Select the correct Inductor
value selection guide from Figures 3, 4, 5 or Figure 6.
(Output voltages of 3.3V, 5V, 12V or 15V respectively).
For other output voltages, see the design procedure for
the adjustable version. B. From the inductor value
selection guide, identify the inductance region intersected
by VIN(Max) and ILOAD(Max), and note the inductor code
for that region. C. Identify the inductor value from the
inductor code, and select an appropriate inductor from
the table shown in Figure 3. Part numbers are listed for
three inductor manufacturers. The inductor chosen must
be rated for operation at the LM2576 switching frequency
(52 kHz) and for a current rating of 1.15 x ILOAD. For
additional inductor information, see the inductor section
in the Application Hints section of this data sheet.
2. Output Capacitor Selection (COUT) A. The value of
the output capacitor together with the inductor defines
the dominate pole-pair of the switching regulator loop.
For stable operation and an acceptable output ripple
voltage, (approximately 1% of the output voltage) a value
between 100 µF and 470 µF is recommended. B. The
capacitor’s voltage rating should be at least 1.5 times
greater than the output voltage. For a 5V regulator, a
rating of at least 8V is appropriate, and a 10V or 15V
rating is recommended. Higher voltage electrolytic
capacitors generally have lower ESR numbers, and for
this reason it may be necessary to select a capacitor
rated for a higher voltage than would normally be
needed.
3. Catch Diode Selection (D1) A.The catch-diode
current rating must be at least 1.2 times greater than the
maximum load current. Also, if the power supply design
must withstand a continuous output short, the diode
should have a current rating equal to the maximum
current limit of the LM2576. The most stressful condition
for this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at
least 1.25 times the maximum input voltage.
4. Input Capacitor (CIN) An aluminum or tantalum
electrolytic bypass capacitor located close to the
regulator is needed for stable operation.
EXAMPLE (Fixed Output Voltage Versions)
Given: VOUT = 5V VIN(Max) = 15V ILOAD(Max) = 3A
1. Inductor Selection (L1) A. Use the selection guide
shown in Figure 4. B. From the selection guide, the
inductance area intersected by the 15V line and 3A line
is L100. C. Inductor value required is 100 µH. From the
table in Figure 3. Choose AIE 415-0930, Pulse
Engineering PE92108, or Renco RL2444.
2. Output Capacitor Selection (COUT) A. COUT = 680
µF to 2000 µF standard aluminum electrolytic.
B.Capacitor voltage rating = 20V.
3. Catch Diode Selection (D1) A.For this example, a 3A
current rating is adequate. B. Use a 20V 1N5823 or
SR302 Schottky diode, or any of the suggested
fast-recovery diodes shown in Figure 8.
4. Input Capacitor (CIN) A 100 µF, 25V aluminum
electrolytic capacitor located near the input and ground
pins provides sufficient bypassing.
11 www.national.com
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LM2576.PDF ] | |
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