MICREL LM2576

LM2576
Micrel
LM2576
52kHz Simple 3A Buck Voltage Regulator
General Description
Features
The LM2576 series of monolithic integrated circuits provide
all the active functions for a step-down (buck) switching
regulator. Fixed versions are available with a 3.3V, 5V, or 12V
fixed output. Adjustable versions have an output voltage
range from 1.23V to 37V. Both versions are capable of driving
a 3A load with excellent line and load regulation.
These regulators are simple to use because they require a
minimum number of external components and include internal
frequency compensation and a fixed-frequency oscillator.
The LM2576 series offers a high efficiency replacement for
popular three-terminal adjustable linear regulators. It
substantially reduces the size of the heat sink, and in many
cases no heat sink is required.
A standard series of inductors available from several different
manufacturers are ideal for use with the LM2576 series. This
feature greatly simplifies the design of switch-mode power
supplies.
The feedback voltage is guaranteed to ±2% tolerance for
adjustable versions, and the output voltage is guaranteed to
±3% for fixed versions, within specified input voltages and
output load conditions. The oscillator frequency is guaranteed
to ±10%. External shutdown is included, featuring less than
200µA standby current. The output switch includes cycle-bycycle current limiting and thermal shutdown for full protection
under fault conditions.
• 3.3V, 5V, 12V, and adjustable output versions
• Voltage over specified line and load conditions:
Fixed version: ±3% max. output voltage
Adjustable version: ±2% max. feedback voltage
• Guaranteed 3A output current
• Wide input voltage range:
4V to 40V
• Wide output voltage range
1.23V to 37V
• Requires only 4 external components
• 52kHz fixed frequency internal oscillator
• Low power standby mode IQ typically < 200µA
• 80% efficiency (adjustable version typically > 80%)
• Uses readily available standard inductors
• Thermal shutdown and current limit protection
• 100% electrical thermal limit burn-in
Applications
•
•
•
•
•
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator for linear regulators
On-card switching regulators
Positive to negative converter (inverting Buck-Boost)
Isolated Flyback Converter using minimum number of
external components
• Negative Boost Converter
Typical Applications
870 20
7V–40V
Unregulated
DC Input
1
4
+5V, 3A
Regulated
Output
Feedback
LM2576-5.0 Output L1
2
100µH
3
5
Gnd On/Off
D1
1N5822
+VIN
+
CIN
100µF
+
COUT
1000µF
Note: Pin numbers are for TO-220 Package
7V–40V
Unregulated
DC Input
1
+VIN
+
CIN
100µF
4
LM2576
3
5
Gnd On/Off
+5V, 3A
Regulated
Output
Feedback
Output L1
2
100µH
D1
1N5822
+
R2 3.09k
COUT
1000µF
R1 1k
Note: Pin numbers are for TO-220 Package
(
VOUT = 1.23 1 + R2
R1
Fixed Regulator in Typical Application
)
Adjustable Regulator in Fixed Output Application
4-120
October 1998
LM2576
Micrel
Ordering Information
Part Number‡
LM2576BT*
Temperature Range
Package
†
–40°C to +85°C
5-lead TO-220
†
–40°C to +85°C
5-lead TO-220
†
LM2576-5.0BT
–40°C to +85°C
5-lead TO-220
†
LM2576-12BT
–40°C to +85°C
5-lead TO-220
LM2576BU*
–40°C to +85°C
5-lead TO-263
LM2576-3.3BU
–40°C to +85°C
5-lead TO-263
LM2576-5.0BU
–40°C to +85°C
5-lead TO-263
LM2576-12BU
–40°C to +85°C
5-lead TO-263
LM2576-3.3BT
* Adjustable output regulators.
† Contact factory for bent or staggered leads option.
4
Pin Configurations
5-LEAD TO-220 (T)
GND
October 1998
5-LEAD TO-263 (U)
5- ON/OFF
4- FEEDBACK
3- GROUND
2- OUTPUT
1- VIN
4-121
GND
5- ON/OFF
4- FEEDBACK
3- GROUND
2- OUTPUT
1- VIN
LM2576
Micrel
Absolute Maximum Ratings (Note 1)
Maximum Supply Voltage
ON/OFF Pin Input Voltage
Output Voltage to Ground (Steady State)
Power Dissipation
Storage Temperature Range
Minimum ESD Rating
C = 100pF, R = 1.5kΩ
FB Pin
Lead Temperature (soldering, 10 sec.)
Maximum Junction Temperature
Operating Ratings
45V
–0.3V ≤ V ≤ +40V
–1V
Internally Limited
–65°C to +150°C
–40°C ≤ TJ ≤ +125°C
40V
Temperature Range
Supply Voltage
2 kV
1 kV
260°C
150°C
Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply
over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 500mA.
LM2576
Symbol
Parameter
Conditions
Typ
Limit
(Note 2)
Units
(Limits)
1.217
1.243
V
V(min)
V(max)
1.193/1.180
1.267/1.280
V
V(min)
V(max)
SYSTEM PARAMETERS, ADJUSTABLE REGULATORS (Note 3) Test Circuit Figure 1
VOUT
Feedback Voltage
VIN = 12V , ILOAD = 0.5A
VOUT = 5V
1.230
VOUT
Feedback Voltage
LM2576
0.5A ≤ ILOAD ≤ 3A, 6V ≤ VIN ≤ 40V
VOUT = 5V
1.230
η
Efficiency
VIN = 12V, ILOAD = 3A, VOUT = 5V
82
%
SYSTEM PARAMETERS, 3.3V REGULATORS (Note 3) Test Circuit Figure 1
VOUT
Output Voltage
VIN = 12V , ILOAD = 0.5A
VOUT = 3.3V
3.3
VOUT
Output Voltage
LM2576-3.3
0.5A ≤ ILOAD ≤ 3A, 6V ≤ VIN ≤ 40V
VOUT = 3.3V
3.3
η
Efficiency
VIN = 12V, ILOAD = 3A
75
3.234
3.366
V
V(min)
V(max)
3.168/3.135
3.432/3.465
V
V(min)
V(max)
%
SYSTEM PARAMETERS, 5V REGULATORS (Note 3) Test Circuit Figure 1
VOUT
Output Voltage
VIN = 12V , ILOAD = 0.5A
VOUT = 5V
5.0
VOUT
Output Voltage
LM2576-5.0
0.5A ≤ ILOAD ≤ 3A, 8V ≤ VIN ≤ 40V
VOUT = 5V
5.0
η
Efficiency
VIN = 12V, ILOAD = 3A
82
4.900
5.100
V
V(min)
V(max)
4.800/4.750
5.200/5.250
V
V(min)
V(max)
%
SYSTEM PARAMETERS, 12V REGULATORS (Note 3) Test Circuit Figure 1
VOUT
Output Voltage
VIN = 25V , ILOAD = 0.5A
VOUT = 12V
12
VOUT
Output Voltage
LMLM2576-12
0.5A ≤ ILOAD ≤ 3A, 15V ≤ VIN ≤ 40V
VOUT = 12V
12
η
Efficiency
VIN = 25V, ILOAD = 3A
88
4-122
11.760
12.240
V
V(min)
V(max)
11.520/11.400
12.480/12.600
V
V(min)
V(max)
%
October 1998
LM2576
Micrel
Electrical Characteristics (continued)
Symbol
Parameter
Conditions
LM2576
Units
Typ
Limit
(Note 2)
(Limits)
50
100/500
nA
47/42
58/63
kHz
kHz (min)
kHz (max)
1.8/2.0
V
V(max)
93
%
%(min)
4.2/3.5
6.9/7.5
A
A(min)
A(max)
DEVICE PARAMETERS, ADJUSTABLE REGULATOR
IB
Feedback Bias Current
VOUT = 5V
DEVICE PARAMETERS, FIXED and ADJUSTABLE REGULATORS
fO
Oscillator Frequency
VSAT
Saturation Voltage
DC
Max Duty Cycle (ON)
ICL
Current Limit
IL
Output Leakage Current
52
IOUT = 3A (Note 4)
1.4
(Note 5)
98
Peak Current, tON ≤ 3µs (Note 4)
VIN = 40V, (Note 6),
(Note 6)
Output = 0V
Output = –1V
Output = –1V
IQ
Quiescent Current
ISTBY
Standby Quiescent
Current
ON/OFF Pin = 5V (OFF)
θJA
θJA
θJC
Thermal Resistance
T,U Package, Junction to Ambient (Note 7)
T,U Package, Junction to Ambient (Note 8)
T,U Package, Junction to Case
October 1998
(Note 6)
5.8
2
30
mA(max)
mA
mA(max)
10
mA
mA(max)
200
µA
µA(max)
7.5
5
50
4-123
65
45
2
°C/W
4
LM2576
Micrel
Electrical Characteristics (continued)
Symbol
Parameter
Conditions
Typ
LM2576
Units
Limit
(Note 2)
(Limits)
2.2/2.4
1.0/0.8
V(min)
V(max)
30
µA
µA(max)
10
µA
µA(max)
ON/OFF CONTROL, FIXED and ADJUSTABLE REGULATORS Test Circuit Figure 1
VIH
VIL
ON/OFF Pin Logic
Input Level
VOUT = 0V
VOUT = 5V
IIH
ON /OFF Pin Logic
Current
ON /OFF Pin = 5V (OFF)
IIL
1.4
1.2
4
ON/OFF Pin = 0V (ON)
0.01
Note 1:
Absolute Maximum Rating indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device
is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical
Characteristics.
Note 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 extreme are guaranteed via testing.
Note 3:
External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the
LM2576/LM1576 is used as shown in Figure 1 test circuit, system performance will be shown in system parameters section of Electrical
Characteristics.
Note 4:
Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output.
Note 5:
Feedback (pin 4) removed from output and connected to 0V.
Note 6:
Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF.
Note 7:
Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/2" leads in a socket, or
on PC board with minimum copper area.
Note 8:
Junction to ambient thermal resistance (no external heat sink) for the 5-lead TO-220 package mounted vertically, with 1/4" leads soldered to PC
board containing approximately 4 square inches of copper area surrounding the leads.
Note 9:
Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper will lower
thermal resistance further.
Typical Performance Characteristics
Feedback Voltage
vs Duty Cycle*
20
25
20
15
10
5
ILOAD = 200 mA
VIN = 12V
ILOAD = 200mA
Normalized to TJ = 25˚C
FEEDBACK VOLTAGE CHANGE (mV)
NORMALIZED FEEDBACK VOLTAGE (mV)
Normalized
Feedback Voltage*
0
-5
-10
-15
-20
-25
-75 -50 -25 0
25 50 75 100 125 150
15
10
5
VIN = 40V
0
-5
VIN = 7V
-10
-15
-20
0
JUNCTION TEMPERATURE (˚C)
20
40
60
80
100
DUTY CYCLE (%)
* Adjustable version only
4-124
October 1998
LM2576
Micrel
Typical Performance Characteristics (continued)
Supply Current
vs. Duty Cycle
Supply Current
14
12
10
ILOAD to 1A
12.5
10.0
5.0
6
VIN from 7V to 40V
2.5
0
10
20
30
40
50
0
60
0
20
INPUT VOLTAGE (V)
SATURATION VOLTAGE (V)
OUTPUT CURRENT (A)
VIN = 12V
6.0
5.5
5.0
4.5
95
1.2
1.0
0.8
25˚C
0.6
150˚C
3.0
2.5
2.0
VOUT = 1.23V
ILOAD = 200 mA
1A
3A
0
-25
-50
-75
-100
-75 -50 -25 0
25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C)
October 1998
1.0
1.5
2.0
2.5
3.0
0
14
12
8
6
4
2
0
-2
-4
5
10
15
20
25 30 35 40
100
75
50
25
0
-25
-50
-75
-6
0
10 15 20
Feedback Pin Current
Normalized to V IN = 10V
VOUT = 5V
ILOAD = 500mA
TJ = 25
10
5
INPUT VOLTAGE (V)
Line Regulation
25
-100
-75 -50 -25 0
30
INPUT VOLTAGE (V)
25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C)
Oscillator Frequency
Dropout Voltage
2.0
Normalized at 25˚C
+6
NORMALIZED FREQUENCY (%)
OUTPUT VOLTAGE CHANGE (mV)
25
4
VOUT = 3V
60
0.5
SWITCH CURRENT (A)
+8
3A
75
65
Normalized
Output Voltage
50
200 mA
70
25 50 75 100 125 150
VIN = 12V
ILOAD = 200mA
Normalized to TJ = 25˚C
200 mA
80
0.2
JUNCTION TEMPERATURE (˚C)
1A
85
0.4
0
NORMALIZED FEEDBACK VOLTAGE (mV)
INPUT VOLTAGE (V)
3.5
VOUT = 12V
90
-55˚C
0
4.0
75
Efficiency
1.4
25 50 75 100 125 150
5.0
4.5
100
JUNCTION TEMPERATURE (˚C)
100
Minimum Operating
Voltage
0.5
0
-75 -50 -25 0
0
-75 -50 -25 0 25 50 75 100 125 150
100
1.5
JUNCTION TEMPERATURE (˚C)
1.0
80
Switch
Saturation Voltage
6.5
1.5
60
VIN = 12V
50
DUTY CYCLE (%)
Current Limit
4.0
-75 -50 -25 0
40
VON/OFF = 5V
100
STANDBY QUIESCENT CURRENT (µA)
4
ILOAD = 200 mA
VIN = 40V
150
+4
+2
0
-2
VIN = 40V
-4
--6
VIN = 12V
-8
-75 -50 -25 0 25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C)
4-125
INPUT-OUTPUT DIFFERENTIAL (V)
8
15.0
7.5
200
STANDBY QUIESCENT CURRENT (µA)
16
17.5
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
20.0
Measured at
Ground Pin
TJ = 25˚C
VOUT = 5V
18
Standby
Quiescent Current
EFFICIENCY (%)
20
(Circuit of Figure 1)
ILOAD = 3A
L1 = 330 µH
1.5
ILOAD = 1A
1.0
0.5
ILOAD = 200 mA
0
-75 -50 -25 0
25 50 75 100 125 150
JUNCTION TEMPERATURE (˚C)
LM2576
Micrel
Typical Performance Characteristics (Circuit of Figure 1)
Load Transient Response
+100mV
Output
Voltage
Change
0
-100mV
3A
Output
Current
2A
1A
0
100 µS/div.
Switching Waveforms
50V
A
0
4A
B
2A
0
4A
C
2A
0
D
5 µS/div.
V OUT = 5V VIN = 45V
A: Output pin voltage 50V/div
B: Output pin current 2A/div
C: Inductor current 2A/div
D: Output ripple voltage 50 mV/div., AC coupled
Horizontal Time Base: 5µS/div
4-126
October 1998
LM2576
Micrel
Test Circuits and Layout Guidelines
FEEDBACK
+VIN
4
LM2575
7V - 40V
UNREGULATED
DC INPUT
+
100 µF
GND 3
ON/OFF 5
VOUT
5.00V
L1
OUTPUT
1
330 µH
2
+
D1
MBR360
CIN
R2
COUT
470µF
CIN — 100µF, 75V Aluminum Electrolytic
COUT — 470µF, 15V Aluminum Electrolytic
D1 — Schottky, MBR360
L1 — 330µH, 415-0926 (AIE)
R1 — 1k, 0.01%
R2 — 3.065k, 0.01%
5-pin TO-220 socket—2936 (Loranger Mfg. Co.)
4-pin TO-3 socket—8112-AG7 (Augat Inc.)
L
O
A
D
R1
FEEDBACK
+VIN
4
LM2575-5.0
7V - 40V
UNREGULATED
DC INPUT
+
100 µF
GND 3
ON/OFF 5
VOUT
5.00V
L1
OUTPUT
1
330 µH
2
+
D1
11DQ06
CIN
CIN — 100µF, 75V Aluminum Electrolytic
COUT — 330µF, 15V Aluminum Electrolytic
D1 — Schottky, 11DQ06
L1 — 100µH, 415-0926 (AIE)
5-pin TO-220 socket—2936 (Loranger Mfg. Co.)
4-pin TO-3 socket—8112-AG7 (Augat Inc.)
L
O
A
D
COUT
220µF
Note: Pin numbers are for TO-220 Package
Figure 1.
As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance generate voltage transients
which can cause problems. For minimal stray inductance and ground loops, the length of the leads indicated by heavy lines should be kept as
short as possible. Single-point grounding (as indicated) or ground plane construction should be used for best results.
Block Diagrams
V IN
1
FEEDBACK
4
INTERNAL
REGULATOR
V IN
INTERNAL
REGULATOR
1
+
-
52 kHz
OSCILLATOR
FEEDBACK
3 AMP
SWITCH
COMPARATOR
-
ON/OFF
4
ON/OFF
-
DRIVER
RESET
THERMAL
SHUTDOWN
CURRENT
LIMIT
2
OUTPUT
2
OUTPUT
3
GND
1.23V
BAND-GAP
REFERENCE
3
GND
3 AMP
SWITCH
COMPARATOR
+
+
-
52 kHz
OSCILLATOR
DRIVER
RESET
THERMAL
SHUTDOWN
CURRENT
LIMIT
Note: Pin numbers are for the TO-220 package
Fixed Regulator
October 1998
5
FIXED GAIN
ERROR AMP
+
1.23V
BAND-GAP
REFERENCE
ON/OFF
FIXED GAIN
ERROR AMP
3.1k
1.0k
5
ON/OFF
Adjustable Regulator
4-127
4