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PDF LM2574 Data sheet ( Hoja de datos )
| Número de pieza | LM2574 | |
| Descripción | Step-Down Switching Regulator | |
| Fabricantes | ON Semiconductor | |
| Logotipo |  |
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LM2574, NCV2574
0.5 A, Adjustable Output
Voltage, Step-Down
Switching Regulator
The LM2574 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 0.5 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 LM2574 are offered by several
different inductor manufacturers.
Since the LM2574 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 most cases, the power dissipated by the LM2574 regulator is so low,
that the copper traces on the printed circuit board are normally the only
heatsink needed and no additional heatsinking is required.
The LM2574 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 60 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% max
over Line and Load Conditions
• Guaranteed 0.5 A Output Current
• Wide Input Voltage Range: 4.75 to 40 V
• 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
• NCV Prefix for Automotive and Other Applications Requiring Site
www.onsemi.com
16
1
8
1
SO−16 WB
DW SUFFIX
CASE 751G
PDIP−8
N SUFFIX
CASE 626
PIN CONNECTIONS
*1
*2
FB 3
Sig Gnd 4
ON/OFF 5
Pwr Gnd 6
*7
*8
16 *
15 *
14 Output
13 *
12 Vin
11 *
10 *
9*
(Top View)
FB 1
Sig Gnd 2
ON/OFF 3
Pwr Gnd 4
8*
7 Output
6*
5 Vin
(Top View)
* No internal connection, but should be soldered to
* PC board for best heat transfer.
and Control Changes
• Pb−Free Packages are Available*
Applications
• Simple and High−Efficiency Step−Down (Buck) Regulators
• Efficient Pre−regulator for Linear Regulators
• On−Card Switching Regulators
• Positive to Negative Converters (Buck−Boost)
• Negative Step−Up Converters
• Power Supply for Battery Chargers
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 24 of this data sheet.
*For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting
Techniques Reference Manual, SOLDERRM/D.
© Semiconductor Components Industries, LLC, 2015
January, 2015 − Rev. 9
1
Publication Order Number:
LM2574/D
1 page  
LM2574, NCV2574
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16)
1.0
0.8 Vin = 20 V
0.6
ILoad = 100 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 60
75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 2. Normalized Output Voltage
125
1.4
1.2 ILoad = 100 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
L = 300 mH
1.5
1.0
0.5
ILoad = 500 mA
ILoad = 100 mA
0
-50 -25
0
25 60
75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 4. Dropout Voltage
125
1.4
1.3 Vin = 25 V
1.2
1.1
1.0
0.9
0.8
0.7
-50
-25
0 25 60 75
TJ, JUNCTION TEMPERATURE (°C)
Figure 5. Current Limit
100
125
20
18 Vout = 5.0 V
Measured at
16 Ground Pin
TJ = 25°C
14
12 ILoad = 500 A
10
8.0 ILoad = 100 mA
6.0
4.0
0 5.0 10 15 20 25 30 35 40
Vin, INPUT VOLTAGE (V)
Figure 6. Quiescent Current
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 60 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 7. Standby Quiescent Current
125
www.onsemi.com
5
5 Page 
LM2574, NCV2574
Procedure (Fixed Output Voltage Version) (continued) In order to simplify the switching regulator design, a step−by−step
design procedure and example is provided.
Procedure
Example
5. Output Capacitor Selection (Cout)
A. Since the LM2574 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
100 mF and 470 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 = 100 mF to 470 mF standard aluminium electrolytic.
B. Capacitor voltage rating = 20 V.
Procedure (Adjustable Output Version: LM2574−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 kW and 5.0 kW. (For best
temperature coefficient and stability with time, use 1% metal
film resistors).
ǒ ǓR2 + R1
Vout
Vref
*
1.0
Given Parameters:
Vout = 24 V
Vin(max) = 40 V
ILoad(max) = 0.4 A
Example
1. Programming Output Voltage (selecting R1 and R2)
Select R1 and R2 :
ǒ ǓVout = 1.23
1.0
)
R2
R1
Select R1 = 1.0 kW
ǒ Ǔ ǒ ǓR2 + R1
Vout
Vref
*
1.0
10 V
+ 1.0 k 1.23 V * 1.0
R2 = 18.51 kW, choose a 18.7 kW 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
“EXTERNAL COMPONENTS” 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
LM2574 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 22 mF aluminium electrolytic capacitor located near the
input and ground pin provides sufficient bypassing.
3. Catch Diode Selection (D1)
A. For this example, a 1.0 A current rating is adequate.
B. Use a 50 V MBR150 Schottky diode or any suggested
fast recovery diodes in Table 1.
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11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LM2574.PDF ] | |
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