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3.0A, 15V, Step-Down Switching Regulator
FEATURES
3.3V, 5.0V, 12V, 15V, and Adjustable Output Versions
Adjustable Version Output Voltage Range, 1.23 to 37V
+/- 4% AG10Maximum Over Line and Load Conditions
Guaranteed 3.0A Output Current
Wide Input Voltage Range
Requires Only 4 External Components
52kHz 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) Equals1
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
LM2576
TO-220
TO-220V
TO-263(D2)
1. Vin
2. Output
3. Ground
4. Feedback
5. On/Off
DESCRIPTION
The LM2576 series of regulators are monolithic integrated
circuits ideally suited for easy and convenient design of a
step-down switching regualtor(buck converter).
All circuits of this series are capable of driving a 3.0A load
with excellent line and load regulation. These devices are
available in fixed output voltages of 3.3V, 5.0V,12V, 15V,
and an adjustable output version.
These regulatiors were designed to minimize the number of externalcomponents 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 limear reguators, 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 0oC to 125 oC).
External shutdown is included, featuring 80 Ua(typical) standby current. The output switch includes
cycle-bycycle current limiting, as well as thermal shutdown for full protection under fault conditions.
ORDERING INFORMATION
Device Marking Package
LM2576T-X.X LM2576T-X.X
LM2576TV-X.X LM2576T-X.X
LM2576R LM2576R-X.X TO-263
TO-220
TO-220V
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3.0A, 15V, Step-Down Switching Regulator
Typical Application (Fixed Output Voltage Versions)
LM2576
Figure 1. Block Diagram and Typical Application
ABSOLUTE MAXIMUM RATINGS
(Absolute Maximum Ratings indicate limits beyond which damage to the device may
TO-220, 5-Lead
Thermal Resistance, Junction-to-Ambient
Thermal Resistance, Junction-to-case
TO-263
Thermal Resistance, Junction-to-Ambient
Thermal Resistance, Junction-to-case
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3.0A, 15V, Step-Down Switching Regulator
LM2576
OPERATING RATINGS (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.)
ELECTRICAL CHARACTERISTICS / SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 15)
(Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for
the 12 V version, and Vin = 30 V for the 15 V version. ILoad = 500 mA. For typical values TJ = 25°C,
for min/max values TJ is the operating junction temperature range that applies [Note 2], unless
otherwise noted.)
1. External components such as the catch diode, inductor, input and output capacitors can affect
switching regulator system performance.
When the LM2576 is used as shown in the Figure 15 test circuit, system performance will be as
shown in system parameters section .
2. Tested junction temperature range for the LM2576: Tlow = –40°C Thigh = +125°C
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3.0A, 15V, Step-Down Switching Regulator
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LM2576
ELECTRICAL CHARACTERISTICS / Device Parameters
(Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for the 12
V version, and Vin = 30 V for the 15 V version. ILoad = 500 mA. For typical values TJ = 25°C, for min/ma
values TJ is the operating junction temperature range that applies [Note 2], unless otherwise noted.)
3. The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload
which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. This
self protection feature lowers the average dissipation of the IC by lowering the minimum duty cycle from 5%
down to approximately 2%.
4. Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.
5. Feedback (Pin 4) removed from output and connected to 0 V.
6. Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and
5.0V ersions, and +25 V for the 12 V and15 V versions, to force the output transistor “off”.
7. Vin = 40 V.
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3.0A, 15V, Step-Down Switching Regulator
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
LM2576
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3.0A, 15V, Step-Down Switching Regulator
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)
LM2576
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3.0A, 15V, Step-Down Switching Regulator
[ TYPICAL PERFORMANCE CHARACTERISTICS ]
LM2576
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3.0A, 15V, Step-Down Switching Regulator
LM2576
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3.0A, 15V, Step-Down Switching Regulator
PIN FUNCTION DESCRIPTION
LM2576
Symbol
1
5 ON/OFF
Vin
Output2
Gnd3
Feedback4
Description
This pin is the positive input supply for the LM2576 step–down switching
regulator.In order to minimize voltage transients and to supply the switching
currents needed by the regulator, a suitable input bypass capacitor must be
present .(Cin in Figure 1).
This is the emitter of the internal switch. The saturation voltage Vsat of this
output switch is typically 1.5 V. It should be kept in mind that the PCB area
connected to this pin should be kept to a minimum in order to minimize
coupling to sensitive circuitry.
Circuit ground pin. See the information about the printed circuit board layout.
This pin senses regulated output voltage to complete the feedback loop.
The signal is divided by the internal resistor divider network R2, R1 and
applied to the non–inverting input of the internal error amplifier. In the
Adjustable version of the LM2576 switching regulator this pin is the direct
input of the error amplifier and the resistor network R2, R1 is connected
externally to allow programming of the output voltage.
It allows the switching regulator circuit to be shut down using logic level
signals, thus dropping the total input supply current to approximately 80 mA.
The threshold voltage is typically 1.4 V. Applying a voltage above this value
(up to +Vin) shuts the regulator off. If the voltage applied to this pin is lower
than 1.4V or if this pin is left open, the regulator will be in the "on" condition
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