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LM2574
Micrel
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 cycle-bycycle 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)
Ordering Information
Part Number LM2574BN LM2574-3.3BN LM2574-5.0BN 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
Typical Application
40V MAX UNREGULATED DC IN VIN CIN 22F PWR GND LM2574 SIG GND OUT ON/ OFF 11DQ05 330H FB REGULATED OUTPUT 0.5A
COUT 220F
Figure 1. Fixed Output Regulator Circuit
Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com
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LM2574
Micrel
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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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)
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. Symbol Parameter Regulators(3), Condition Test Circuit Figure 2 VIN = 12V, ILOAD = 0.1A, VOUT = 5V 0.1A ILOAD 0.5A, 7V VIN 40V, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V Regulators(3), Test Circuit Figure 3 VIN = 12V, ILOAD = 0.1A, VOUT = 3.3V 0.1A ILOAD 0.5A, 4.75V VIN 40V, VOUT = 3.3V VIN = 12V, ILOAD = 0.1A Regulators(3), Test Circuit Figure 3 VIN = 12V, ILOAD = 0.1A, VOUT = 5V 0.1A ILOAD 0.5A, 7V VIN 40V, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V 4.900 4.800 4.750 5.0 5.0 78 5.100 5.200 5.250 V V V % 3.234 3.168 3.135 3.3 3.3 73 3.366 3.432 3.465 V V V % 1.217 1.193 1.180 1.230 1.230 78 1.243 1.267 1.280 V V V % Min Typ Max Units System Parameters, Adjustable VOUT VOUT Feedback Voltage Feedback Voltage (LM2574) Efficiency
System Parameters, 3.3V VOUT VOUT
Output Voltage Output Voltage (LM2574-3.3) Efficiency
System Parameters, 5V VOUT VOUT
Notes:
Output Voltage Output Voltage (LM2574-5.0) Efficiency
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 Charac-
teristics."
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Electrical Characteristics
Symbol Parameter Condition Min Typ Max Units Device Parameters, Adjustable Regulator IB Feedback Bias Current VOUT = 5V 50 100 500 nA nA
Device Parameters, Fixed and Adjustable Regulators fo VSAT DC ICL IL IQ ISTBY JA 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.
Oscillator Frequency Saturation Voltage Max Duty Cycle (ON) Current Limit Output Leakage Current Quiescent Current Standby Quiescent Current Thermal Resistance
Note 8 IOUT = 0.5A(4) Note 5 Peak Current, tON 3s(4)
47 42
52 0.8
58 63 1.2 1.4
kHz kHz V V %
93 0.7 0.65
98 1.0 1.6 1.8 2 30 10 200
A mA mA A C/W
VIN, Note 6, Output = 0V Note 6, Output = -1V Note 6 ON/OFF Pin = 5V (OFF) N Package, Junction to Ambient(7)
7.5 5 50 85
On/Off Control, Fixed and Adjustable Regulators Test Circuit Figures 2, 3 ON/OFF Input Level ON/OFF Input Level ON/OFF Logic Current ON/OFF Logic Current VOUT = 0V VOUT = 5V ON/OFF = 5V (OFF) ON/OFF = 0V (ON) 2.2 2.4 1.4 1.2 4 0.01 1.0 0.8 30 10 V V V V A A
Test Circuit
FB VIN CIN 22F LM2574 (adjustable) OUT PWR SIG ON/ GND GND OFF 330H 3.09k 11DQ06 COUT 220F 1k
Figure 2. Adjustable Regulator Test Circuit
FB VIN CIN 22F PWR GND LM2574- 3.3, 5 OUT SIG ON/ GND OFF 11DQ06 330H
COUT 220F
Figure 3. Fixed Regulator Test Circuit
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Load
Load
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LM2574
Micrel
Typical Characteristics (Circuit of Figure 1)
Supply Current vs. Duty Cycle
STANDBY QUIESCENT CURRENT (A)
Supply Current
20 18
SUPPLY CURRENT (mA)
Standby Quiescent Current
200 VIN = 40V
16 14 12 10 8 6 4 0 10 20 30
SUPPLY CURRENT (mA)
Measured at Ground Pin TJ = 25C VOUT = 5V
20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 VIN from 7V to 40V 0 20 40 60 80 100 ILOAD = 100 mA
150 VON/OFF = 5V VIN = 12V 50
100
ILOAD to 0.5A
40
50
60
0
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
INPUT VOLTAGE (V)
DUTY CYCLE (%)
Current Limit
1.5 VI N = 25V
SATURATION VOLTAGE (V) OUTPUT CURRENT (A)
Switch Saturation Voltage
1.1 100 95 0.9 -55C -40C 0.7 25C
EFFICIENCY (%)
Efficiency
VOUT = 12V 0.5A 100 mA 100 mA 0.5A VOUT = 3V
90 85 80 75 70 65 60 0 0.1 0.2 0.3 0.4 0.5 0 5 10 15 20 25 30
INPUT VOLTAGE (V)
1
0.5
0.5 125C 150C 0.3
SWITCH CURRENT (A)
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
35 40
Minimum Operating Voltage
NORMALIZED FEEDBACK VOLTAGE (mV)
Line Regulation
Normalized to V IN = 10V VOUT = 5V ILOAD = 100mA TJ = 25
STANDBY QUIESCENT CURRENT (nA)
Feedback Pin Current
100 75 50 25 0 -25 -50 -75 -100 -75 -50 -25 0 25 50 75 100 125 150
5.0 4.5 4.0
INPUT VOLTAGE (V)
14 12 10 8 6 4 2 0 -2 -4 -6 0
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -75 -50 -25 0 VOUT = 1.23V ILOAD = 100 mA 25 50 75 100 125 150
5
10
15
20
25
30
JUNCTION TEMPERATURE (C)
INPUT VOLTAGE (V)
JUNCTION TEMPERATURE (C)
Normalized Output Voltage
100
OUTPUT VOLTAGE CHANGE (mV)
Oscillator Frequency
+8 +6
NORMALIZED FREQUENCY (%)
Dropout Voltage
2.0
INPUT-OUTPUT DIFFERENTIAL (V)
75 50 25 0 -25 -50 -75
VIN = 12V ILOAD = 100mA Normalized to TJ = 25C VOUT = 5V
Normalized at 25C 1.5 ILOAD = 0.5A
VOUT = 5% R IND = 0.2
+4 +2 0 -2 -4 --6 VIN = 40V
1.0 ILOAD = 100 mA
0.5
-100 -75 -50 -25 0
25 50 75 100 125 150
VIN = 12V -8 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
0 -75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (C)
JUNCTION TEMPERATURE (C)
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Typical Performance Characteristics (continued)
Normalized Feedback Voltage*
NORMALIZED FEEDBACK VOLTAGE (mV)
Feedback Voltage vs Duty Cycle*
20
FEEDBACK VOLTAGE CHANGE (mV)
25 20 15 10 5 0 -5 -10 -15 -20 -25 -75 -50 -25 0 VIN = 12V ILOAD = 100mA Normalized to TJ = 25C
15 10 5 0 -5 -10 -15 -20 0 20 40
ILOAD = 100 mA
VIN = 40V
VIN = 7V
25 50 75 100 125 150
60
80
100
JUNCTION TEMPERATURE (C)
DUTY CYCLE (%)
* Adjustable version only
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Block Diagrams
V IN FEEDBACK
1 4
3.1k
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
V IN
1
INTERNAL REGULATOR
ON/OFF
5
ON/OFF
FIXED GAIN ERROR AMP
FIXED GAIN ERROR AMP COMPARATOR 1/2 AMP SWITCH FEEDBACK
+
1.0k
4
+ + -
COMPARATOR
1/2 AMP SWITCH
-
+ -
DRIVER
DRIVER
2
1.23V BAND-GAP REFERENCE
OUTPUT 1.23V BAND-GAP REFERENCE
2
OUTPUT
52 kHz OSCILLATOR
RESET
THERMAL SHUTDOWN
CURRENT LIMIT
3
GND
52 kHz OSCILLATOR
RESET
THERMAL SHUTDOWN
CURRENT LIMIT
3
GND
Note: Pin numbers are for the TO-220 package
Fixed Regulator
Adjustable Regulator
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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. 1849 FORTUNE DRIVE
TEL
SAN JOSE, CA 95131
WEB
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
http://www.micrel.com
The 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 proAOkt 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 at Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2003 Micrel, Incorporated. M9999-122303
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