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PDF LM2576 Data sheet ( Hoja de datos )
| Número de pieza | LM2576 | |
| Descripción | Step-Down Switching Regulator | |
| Fabricantes | ON Semiconductor | |
| Logotipo |  |
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LM2576
3.0 A, 15 V, Step−Down
Switching Regulator
The LM2576 series of regulators are monolithic integrated circuits
ideally suited for easy and convenient design of a step−down
switching regulator (buck converter). All circuits of this series are
capable of driving a 3.0 A load with excellent line and load regulation.
These devices are available in fixed output voltages of 3.3 V, 5.0 V,
12 V, 15 V, and an adjustable output version.
These regulators were designed to minimize the number of external
components to simplify the power supply design. Standard series of
inductors optimized for use with the LM2576 are offered by several
different inductor manufacturers.
Since the LM2576 converter is a switch−mode power supply, its
efficiency is significantly higher in comparison with popular
three−terminal linear regulators, especially with higher input voltages.
In many cases, the power dissipated is so low that no heatsink is
required or its size could be reduced dramatically.
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.
The LM2576 features include a guaranteed ±4% tolerance on output
voltage within specified input voltages and output load conditions, and
±10% on the oscillator frequency (±2% over 0°C to 125°C). External
shutdown is included, featuring 80 mA (typical) standby current. The
output switch includes cycle−by−cycle current limiting, as well as
thermal shutdown for full protection under fault conditions.
Features
• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions
• Adjustable Version Output Voltage Range, 1.23 to 37 V ±4%
Maximum Over Line and Load Conditions
• Guaranteed 3.0 A Output Current
• Wide Input Voltage Range
• Requires Only 4 External Components
• 52 kHz Fixed Frequency Internal Oscillator
• TTL Shutdown Capability, Low Power Standby Mode
• High Efficiency
• Uses Readily Available Standard Inductors
• Thermal Shutdown and Current Limit Protection
• Moisture Sensitivity Level (MSL) Equals 1
• Pb−Free Packages are Available
Applications
• Simple High−Efficiency Step−Down (Buck) Regulator
• Efficient Pre−Regulator for Linear Regulators
• On−Card Switching Regulators
• Positive to Negative Converter (Buck−Boost)
• Negative Step−Up Converters
• Power Supply for Battery Chargers
© Semiconductor Components Industries, LLC, 2006
January, 2006 − Rev. 8
1
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1
5
TO−220
TV SUFFIX
CASE 314B
Heatsink surface connected to Pin 3
1
5
TO−220
T SUFFIX
CASE 314D
Pin 1. Vin
2. Output
3. Ground
4. Feedback
5. ON/OFF
1
5
D2PAK
D2T SUFFIX
CASE 936A
Heatsink surface (shown as terminal 6 in
case outline drawing) is connected to Pin 3
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 24 of this data sheet.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 25 of this data sheet.
Publication Order Number:
LM2576/D
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1 page  
LM2576
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
1.0
0.8 Vin = 20 V
0.6
ILoad = 500 mA
Normalized at TJ = 25°C
0.4
0.2
0
−0.2
−0.4
−0.6
−0.8
−1.0
−50 −25
0
25 50
75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 2. Normalized Output Voltage
125
1.4
1.2 ILoad = 500 mA
1.0 TJ = 25°C
0.8
0.6 3.3 V, 5.0 V and ADJ
0.4
0.2
0 12 V and 15 V
−0.2
−0.4
−0.6
0 5.0 10 15 20 25 30 35
Vin, INPUT VOLTAGE (V)
Figure 3. Line Regulation
40
2.0
ILoad = 3.0 A
1.5
1.0
ILoad = 500 mA
0.5
L1 = 150 mH
Rind = 0.1 W
0
−50 −25
0
25 50
75 100 125
TJ, JUNCTION TEMPERATURE (°C)
Figure 4. Dropout Voltage
6.5
Vin = 25 V
6.0
5.5
5.0
4.5
4.0
−50 −25 0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 5. Current Limit
125
20
18
16
14
12
10
8.0
6.0
4.0
0
Vout = 5.0 V
Measured at
Ground Pin
TJ = 25°C
ILoad = 3.0 A
ILoad = 200 mA
5.0 10 15 20 25 30 35
Vin, INPUT VOLTAGE (V)
Figure 6. Quiescent Current
40
200
180
160
140
120
100
80
60
40
20
0
−50
VON/OFF = 5.0 V
Vin = 40 V
Vin = 12 V
−25 0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 7. Standby Quiescent Current
125
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LM2576
Procedure (Fixed Output Voltage Version) (continued)In order to simplify the switching regulator design, a step−by−step
design procedure and some examples are provided.
Procedure
Example
5. Output Capacitor Selection (Cout)
A. Since the LM2576 is a forward−mode switching regulator
with voltage mode control, its open loop 2−pole−1−zero
frequency characteristic has the dominant pole−pair
determined by the output capacitor and inductor values. For
stable operation and an acceptable ripple voltage,
(approximately 1% of the output voltage) a value between
680 mF and 2000 mF is recommended.
B. Due to the fact that the higher voltage electrolytic capacitors
generally have lower ESR (Equivalent Series Resistance)
numbers, the output capacitor’s voltage rating should be at
least 1.5 times greater than the output voltage. For a 5.0 V
regulator, a rating at least 8.0 V is appropriate, and a 10 V or
16 V rating is recommended.
5. Output Capacitor Selection (Cout)
A. Cout = 680 mF to 2000 mF standard aluminium electrolytic.
B. Capacitor voltage rating = 20 V.
Procedure (Adjustable Output Version: LM2576−ADJ)
Procedure
Given Parameters:
Vout = Regulated Output Voltage
Vin(max) = Maximum DC Input Voltage
ILoad(max) = Maximum Load Current
1. Programming Output Voltage
To select the right programming resistor R1 and R2 value (see
Figure 2) use the following formula:
ǒ ǓVout + Vref
1.0 )
R2
R1
where Vref = 1.23 V
Resistor R1 can be between 1.0 k and 5.0 kW. (For best
temperature coefficient and stability with time, use 1% metal
film resistors).
ǒ ǓR2 + R1
Vout
Vref
– 1.0
Example
Given Parameters:
Vout = 8.0 V
Vin(max) = 25 V
ILoad(max) = 2.5 A
1. Programming Output Voltage (selecting R1 and R2)
Select R1 and R2:
ǒ ǓVout + 1.23
1.0 )
R2
R1
Select R1 = 1.8 kW
ǒ Ǔ ǒ ǓR2 + R1
Vout
Vref
*
1.0
+
1.8 k
8.0 V
1.23 V
*
1.0
R2 = 9.91 kW, choose a 9.88 k metal film resistor.
2. Input Capacitor Selection (Cin)
To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +Vin and ground pin GND This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.
For additional information see input capacitor section in the
“Application Hints” section of this data sheet.
3. Catch Diode Selection (D1)
A. Since the diode maximum peak current exceeds the
regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design, the diode should have a
current rating equal to the maximum current limit of the
LM2576 to be able to withstand a continuous output short.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
2. Input Capacitor Selection (Cin)
A 100 mF, 150 V aluminium electrolytic capacitor located near
the input and ground pin provides sufficient bypassing.
3. Catch Diode Selection (D1)
A. For this example, a 3.0 A current rating is adequate.
B. Use a 30 V 1N5821 Schottky diode or any suggested fast
recovery diode in the Table 1.
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| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LM2576.PDF ] | |
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