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LM2574
Micrel, Inc.
LM2574
52kHz Simple 0.5A Buck Regulator
General Description
The LM2574 family is a series of easy to use fixed and adjustable switching voltage regulators. The LM2574 contains all of the active circuitry necessary to construct a stepdown (buck) switching regulator and requires a minimum of external components. The LM2574 is available in 3.3V and 5V fixed output versions, or an adjustable version with an output voltage range of 1.23V to 37V. Output voltage is guaranteed to 4% for specified input and load conditions. The LM2574 can supply 0.5A while maintaining excellent line and load regulation. The output switch includes cycleby-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. An external shutdown connection selects operating or standby modes. Standby current is less than 200A. Heat sinks are generally unnecessary due the regulator's high efficiency. Adequate heat transfer is usually provided by soldering all package pins to a printed circuit board. The LM2574 includes internal frequency compensation and an internal 52kHz fixed frequency oscillator guaranteed to 10% of the frequency. Circuits constructed around the LM2574 use a standard series of inductors which are available from several different manufacturers. All support documentation can be found on Micrel's web site at www.micrel.com.
Features
* 3.3V, 5V, 12V, and adjustable output versions * Adjustable version output 1.23V to 37V 4% max. over line and load conditions. * Guaranteed 0.5A output current * Wide input voltage, up to 40V * Thermal shutdown and current limit protection * Requires only 4 external components. * Shutdown capability (standby mode) * Low power standby mode < 200A Typical * High-efficiency * 52kHz fixed frequency internal oscillator * Uses standard inductors
Applications
* * * * Simple high-efficiency step-down (buck) regulator Efficient pre-regulator for linear regulators On-card switching regulators Positive to negative converter (buck-boost)
Typical Application
40V MAX UNREGULATED DC IN CIN 22F
VIN LM2574 PWR GND
FB
330H
OUT SIG ON/ GND OFF
REGULATED OUTPUT 0.5A COU T 220F
11DQ05
Figure 1. Fixed Output Regulator Circuit
Micrel, Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
July 2005
1
M9999-072805
LM2574
Micrel, Inc.
Ordering Information
Part Number Standard LM2574BN LM2574-3.3BN LM2574-5.0BN Pb-Free LM2574YN LM2574-3.3YN LM2574-5.0YN Junction Temp. Range -40C to +85C -40C to +85C -40C to +85C Package 8-pin Plastic DIP 8-pin Plastic DIP 8-pin Plastic DIP
Pin Configuration
FB 1 SIG GND 2 ON/OFF 3 PWR GND 4
8-Pin DIP (N)
8 NC 7 OUTPUT 6 NC 5 VIN
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LM2574
Micrel, Inc.
Absolute Maximum Ratings(1)
Maximum Supply Voltage LM2574...................................................................... 45V OFF Pin Input Voltage ................................ -0.3V V VIN Output Voltage to Ground (Steady State) ...................... -1V Power Dissipation ..................................... Internally Limited Storage Temperature Range (TS) ............. -65C to +150C Minimum ESD Rating C = 100pF, R = 1.5k ................................................ 2kV FB Pin ........................................................................ 1kV Lead Temperature (soldering, 10 sec.) ...................... 260C
Operating Ratings(1)
Supply Voltage LM2574...................................................................... 40V Temperature Range LM2574...........................................-40C TJ +125C Maximum Junction Temperature (TJ.......................... 150C
Electrical Characteristics(2)
Symbol VOUT VOUT VOUT VOUT VOUT VOUT
Notes: 1. "Absolute Maximum Ratings" indicate limits beyond which damage to the device may occur. "Operating Ratings" indicate for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see "Electrical Characteristics." 2. All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via testing. 3. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2574 is used as shown in Figure 1 test circuit, system performance will be shown in system parameters section of "Electrical Characteristics."
Specifications with standard typeface are for TJ = 25C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 100mA. Parameter Condition Min Typ Max Regulators(3), Test Circuit Figure 2 0.1A ILOAD 0.5A, 7V VIN 40V, VOUT = 5V Test Circuit Figure 3 VIN = 12V, ILOAD = 0.1A, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V 1.217 1.193 1.180 1.230 1.230 78 3.234 3.168 3.135 3.3 3.3 73 4.900 4.800 4.750 5.0 5.0 78 5.100 5.200 5.250 3.366 3.432 3.465 1.243 1.267 1.280
Units V V V % V V V % V V V %
System Parameters, Adjustable Feedback Voltage Feedback Voltage (LM2574) Efficiency
System Parameters, 3.3V
Regulators(3),
Output Voltage Output Voltage (LM2574-3.3) Efficiency Output Voltage Output Voltage (LM2574-5.0) Efficiency
0.1A ILOAD 0.5A, 4.75V VIN 40V, VOUT = 3.3V VIN = 12V, ILOAD = 0.1A
VIN = 12V, ILOAD = 0.1A, VOUT = 3.3V
System Parameters, 5V Regulators(3), Test Circuit Figure 3
0.1A ILOAD 0.5A, 7V VIN 40V, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V
VIN = 12V, ILOAD = 0.1A, VOUT = 5V
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M9999-072805
LM2574
Micrel, Inc.
Parameter Feedback Bias Current Condition VOUT = 5V Min Typ 50 Max 100 500 58 63 1.2 1.4 1.6 1.8 2 30 10 200 Units nA nA kHz kHz V V % A mA mA A C/W V V 1.0 0.8 30 10 V V A A
Electrical Characteristics
Symbol IB Device Parameters, Adjustable Regulator
Device Parameters, Fixed and Adjustable Regulators fo VSAT DC ICL IL IQ Oscillator Frequency Saturation Voltage Max Duty Cycle (ON) Current Limit Output Leakage Current Quiescent Current Standby Quiescent Current Thermal Resistance ON/OFF Input Level ON/OFF Input Level ON/OFF Logic Current ON/OFF Logic Current Note 8 IOUT = 0.5A(4) Note 5 Peak Current, tON 3s(4) VIN, Note 6, Output = 0V Note 6, Output = -1V Note 6 ON/OFF Pin = 5V (OFF) N Package, Junction VOUT = 0V VOUT = 5V ON/OFF = 5V (OFF) ON/OFF = 0V (ON) to Ambient(7) 2.2 2.4 93 0.7 0.65 47 42 52 0.8 98 1.0
7.5 5 50 85 1.4 1.2 4 0.01
ISTBY JA
On/Off Control, Fixed and Adjustable Regulators Test Circuit Figures 2, 3 VIH VIL IIH IIL
Notes: 4. Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input. 5. Feedback (pin 4) removed from output and connected to 0V. 6. Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF. 7. Junction-to-ambient thermal resistance with approximately 1 square inches of PC board copper surrounding the leads.
Test Circuit
VIN FB
CIN 22F
LM2574 (adjustable) OUT PWR SI G ON/ GND GND OFF
330H
11DQ06
COU T 220F
3.09k 1k
Figure 2. Adjustable Regulator Test Circuit
FB
CIN 22F
LM2574- 3.3, 5, 12 OUT P W R S I G ON/ GND GND O F F
VIN
330H
11DQ06
COU T 220F
Figure 3. Fixed Regulator Test Circuit
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LM2574
Micrel, Inc.
Typical Characteristics (Circuit of Figure 1)
Supply Current
20
Supply Current vs. Duty Cycle
20.0 17.5 15.0 12.5 10.0 7.5
Standby Quiescent Current
200 150
18 16 14 12 10 8 6 4 0 10 20 30
Measured at Ground Pin TJ = 25C VOUT = 5V
VIN = 40V
100
I LO AD = 100 mA
VON/OFF = 5V
VIN = 12V
I LO AD to 0.5A
5.0 2.5
50
VIN from 7V to 40V
0 20 40 60 80 100
40
50
60
0
0 -75 -50 -25 0 25 50 75 100 125150 JU N C TI O N TEM PER ATU R E ( C )
INPUT VOLTAGE ( V)
D U TY C YC LE ( % )
Current Limit
1.5
Switch Saturation Voltage
1.1
100
Efficiency
95 VOUT = 12V
V IN = 25V
0.9
1
90
0.5A
100 mA
100 mA
-55C -40C 0.7
85 80 75 70 65
25C
0.5
0.5A
VOUT = 3V
0.5 125C 150C 0.3 0
0 -75 -50 -25 0 25 50 75 100125 150 JU N C TI O N TEM PER ATU R E ( C )
0.1
0.2
0.3
0.4
0.5
60
0
5
10 15 20 25 30
35 40
SW I TC H C U R R EN T ( A)
INPUT VOLTAGE ( V)
Minimum Operating Voltage
5.0 4.5
Line Regulation
14 12
Feedback Pin Current
100
4.0 3.5 3.0 2.5 2.0 1.5 1.0
VOUT = 1.23V I LO AD = 100 mA
10 8 6 4 2 0 -2 -4 -6
0
Normalized toVIN = 10V VOUT = 5V ILO AD = 100mA TJ = 25
75 50 25 0 -25 -50 -75
0.5 0 -75 -50 -25 0 25 50 75 100125150 J U N C TI O N TEM PER ATU R E ( C )
5 10 15 20 25 INPUT VOLTAGE ( V)
30
-100 -75 -50 -25 0 25 50 75 100 125150 JU N C TI O N TEM PER ATU R E ( C )
100
Normalized Output Voltage
VIN = 12V I LO AD = 100mA Normalized toTJ = 25C VOUT = 5V
Oscillator Frequency
+8
75
+6 +4 +2 0 -2 -4 --6
Normalized at 25 C
2.0
Dropout Voltage
I LO AD = 0.5A
VOUT = 5% R IND = 0.2
50
1.5
25
0
1.0
VIN = 40V
-25
-50
0.5
I LO AD = 100 mA
-75
-100 -75 -50 -25 0
25 50 75 100125150
VIN = 12V -8 -75 -50 -25 0 25 50 75 100125150
J U N C TI O N TEM PER ATU R E ( C )
0 -75 -50 -25 0 25 50 75 100125150
JU N C TI O N TEM PER ATU R E ( C )
JU N C TI O N TEM PER ATU R E ( C )
July 2005
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M9999-072805
LM2574
Micrel, Inc.
Typical Performance Characteristics (continued)
25
Normalized Feedback Voltage*
VIN = 12V I LO AD = 100mA Normalized toTJ = 25 C
20
Feedback Voltage vs Duty Cycle*
I LO AD = 100 mA
20
15
15
10 5
10
5
0
0
VIN = 40V
-5 -10
-5
-15
-10
VIN = 7V
-20 -25 -75 -50 -25 0
-15
25 50 75 100125150
-20
0
20
40
60
80
100
JU N C TI O N TEM PER ATU R E ( C )
D U TY C YC LE ( % )
* Adjustable version only
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LM2574
Micrel, Inc.
Block Diagrams
V IN F EED BACK
1
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
V IN
1
FIXED GAIN E R R OR A M P
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
4
3.1k
FIXED GAIN E R R OR A M P
1.0k
+ -
COM PARAT OR
1/2 AMP SW ITCH DRIVER
F EED BACK
4
+ -
+ -
COM PARAT OR
1/2 AMP SW ITCH DRIVER
2
THERMAL SHUTDOWN CURRENT LIMIT
+ -
OUTPUT
2
THERMAL SHUTDOWN CURRENT LIMIT
OUTPUT
1.23V BAND-GAP REFERENCE
52 kHz OSCILLATOR
RESET
3
GND
1.23V BAND-GAP REFERENCE
52 kHz OSCILLATOR
RESET
3
GND
Note: Pin numbers are for the TO-220 package
Fixed Regulator
Adjustable Regulator
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M9999-072805
LM2574
Micrel, Inc.
Package Information
PIN 1 DIMENSIONS: INCH (MM)
0.380 (9.65) 0.370 (9.40)
0.135 (3.43) 0.125 (3.18)
0.255 (6.48) 0.245 (6.22) 0.300 (7.62) 0.013 (0.330) 0.010 (0.254)
0.018 (0.57) 0.100 (2.54)
0.130 (3.30) 0.0375 (0.952)
0.380 (9.65) 0.320 (8.13)
8-Pin DIP (N)
MICREL INC.
TEL
+ 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2003 Micrel, Inc. M9999-072805
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July 2005

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