MOTOROLA LM2576T-015, LM2576T-012, LM2576T-3.3, LM2576TV-ADJ, LM2576TV-3.3 Datasheet

Order this document by LM2576/D

							LM2576
	Easy	Switcher		3.0	A
	Step-Down		Voltage		Regulator	EASY SWITCHER
	The LM2576 series of regulators are monolithic integrated circuits ideally
						3.0 A STEP±DOWN
	suited for easy and convenient design of a step±down switching regulator
						VOLTAGE REGULATOR
	(buck converter). All circuits of this series are capable of driving a 3.0 A load
	with excellent line and load regulation. These devices are available in fixed						SEMICONDUCTOR
	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						TECHNICAL DATA
	components 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					T SUFFIX
	is significantly	higher in comparison		with popular	three±terminal linear
						PLASTIC PACKAGE
	regulators, especially with higher input voltages. In many cases, the power
						CASE 314D
	dissipated is so low that no heatsink is required or its size could be reduced
							1
	dramatically.
						Pin 1.	Vin
	A standard series of inductors optimized for use with the LM2576 are
						2.	Output	5
	available from several different manufacturers. This feature greatly simplifies					3.	Ground
	the design of switch±mode power supplies.					4.	Feedback
	The LM2576 features include a guaranteed ±4% tolerance on output					5. ON/OFF
	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 80 μA (typical) standby current. The output switch
	includes cycle±by±cycle current limiting, as well as thermal shutdown for full					TV SUFFIX		1
	protection under fault conditions.					PLASTIC PACKAGE
	Features					CASE 314B
								5
	• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions					Heatsink surface
	• Adjustable Version Output Voltage Range, 1.23 to 37 V ±4% Maximum					connected to Pin 3.
	Over Line and Load Conditions
	• Guaranteed 3.0 A Output Current
	• Wide Input Voltage Range					D2T SUFFIX
	• Requires Only 4 External Components
						PLASTIC PACKAGE
	• 52 kHz Fixed Frequency Internal Oscillator					CASE 936A		1
						(D2PAK)
	• TTL Shutdown Capability, Low Power Standby Mode							5
	• High Efficiency					Heatsink surface (shown as terminal 6 in case outline
	• Uses Readily Available Standard Inductors
							drawing) is connected to Pin 3.
	• Thermal Shutdown and Current Limit Protection

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

DEVICE TYPE/NOMINAL OUTPUT VOLTAGE

LM2576±3.3	3.3 V
LM2576±5	5.0 V
LM2576±12	12 V
LM2576±15	15 V
LM2576±ADJ	1.23 V to 37 V

ORDERING INFORMATION

	Operating
Device	Temperature Range	Package
LM2576T±XX		Straight Lead
LM2576TV±XX	TJ = ±40° to +125°C	Vertical Mount
LM2576D2T±XX		Surface Mount

XX = Voltage Option, i.e. 3.3, 5, 12, 15 V; and ADJ for

Adjustable Output.

Motorola, Inc. 1999

Rev 1, 07/1999

LM2576

Figure 1. Block Diagram and Typical Application

Typical Application (Fixed Output Voltage Versions)

7.0 V ± 40 V							+Vin
Unregulated
DC Input					1
		Cin
	100 μF

LM2576

3Gnd 5

Feedback
4	L1
Output	100 μH
2	D1	Cout
ON/OFF	1N5822		μF
		1000

5.0 V Regulated

Output 3.0 A Load

	Representative Block Diagram and Typical Application
Unregulated	+Vin		3.1 V Internal	ON/OFF		ON/OFF	Output		R2
DC Input	1		Regulator				Voltage Versions		(Ω)
						5
									1.7 k
	Cin						3.3 V
	4						5.0 V		3.1 k
							12 V		8.84 k
	Feedback			Current			15 V		11.3 k
							For adjustable version
	R2	Fixed Gain		Limit
		Error Amplifier Comparator					R1 = open, R2 = 0 Ω
	R1				Driver				Regulated
		Freq		Latch					Output
	1.0 k						L1
		Shift				Output			Vout
		18 kHz			1.0 Amp	2
	1.235 V
			52 kHz		Switch	Gnd	D1	Cout
	Band±Gap			Reset	Thermal	3			Load
	Reference		Oscillator		Shutdown

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.)

		Rating	Symbol	Value	Unit
	Maximum Supply Voltage		Vin	45	V
			±	±0.3 V ≤ V ≤ +Vin	V
	ON/OFF Pin Input Voltage
	Output Voltage to Ground (Steady±State)		±	±1.0	V
	Power Dissipation
	Case 314B and 314D (TO±220, 5±Lead)		PD	Internally Limited	W
	Thermal Resistance, Junction±to±Ambient		RθJA	65	°C/W
	Thermal Resistance, Junction±to±Case		RθJC	5.0	°C/W
	Case 936A (D2PAK)		P	Internally Limited	W
			D		°C/W
	Thermal Resistance, Junction±to±Ambient		RθJA	70
	Thermal Resistance, Junction±to±Case		RθJC	5.0	°C/W
	Storage Temperature Range		Tstg	±65 to +150	°C
	Minimum ESD Rating (Human Body Model:		±	2.0	kV
	C = 100 pF, R = 1.5 kΩ)
	Lead Temperature (Soldering, 10 seconds)		±	260	°C
	Maximum Junction Temperature		TJ	150	°C

NOTE: ESD data available upon request.

2	MOTOROLA ANALOG IC DEVICE DATA

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.)

Rating	Symbol	Value	Unit
Operating Junction Temperature Range	TJ	±40 to +125	°C
Supply Voltage	Vin	40	V

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 15)

ELECTRICAL CHARACTERISTICS (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.)

Characteristics	Symbol	Min	Typ	Max	Unit
LM2576±3.3 ([Note 1] Test Circuit Figure 15)
Output Voltage (Vin = 12 V, ILoad = 0.5 A, TJ = 25°C)	Vout	3.234	3.3	3.366	V
Output Voltage (6.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A)	Vout				V
TJ = 25°C		3.168	3.3	3.432
TJ = ±40 to +125°C		3.135	±	3.465
Efficiency (Vin = 12 V, ILoad = 3.0 A)	η	±	75	±	%
LM2576±5 ([Note 1] Test Circuit Figure 15)
Output Voltage (Vin = 12 V, ILoad = 0.5 A, TJ = 25°C)	Vout	4.9	5.0	5.1	V
Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A)	Vout				V
TJ = 25°C		4.8	5.0	5.2
TJ = ±40 to +125°C		4.75	±	5.25
Efficiency (Vin = 12 V, ILoad = 3.0 A)	η	±	77	±	%
LM2576±12 ([Note 1] Test Circuit Figure 15)
Output Voltage (Vin = 25 V, ILoad = 0.5 A, TJ = 25°C)	Vout	11.76	12	12.24	V
Output Voltage (15 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A)	Vout				V
TJ = 25°C		11.52	12	12.48
TJ = ±40 to +125°C		11.4	±	12.6
Efficiency (Vin = 15 V, ILoad = 3.0 A)	η	±	88	±	%
LM2576±15 ([Note 1] Test Circuit Figure 15)
Output Voltage (Vin = 30 V, ILoad = 0.5 A, TJ = 25°C)	Vout	14.7	15	15.3	V
Output Voltage (18 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A)	Vout				V
TJ = 25°C		14.4	15	15.6
TJ = ±40 to +125°C		14.25	±	15.75
Efficiency (Vin = 18 V, ILoad = 3.0 A)	η	±	88	±	%
LM2576 ADJUSTABLE VERSION ([Note 1] Test Circuit Figure 15)
Feedback Voltage (Vin = 12 V, ILoad = 0.5 A, Vout = 5.0 V, TJ = 25°C)	Vout	1.217	1.23	1.243	V
Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A, Vout = 5.0 V)	Vout				V
TJ = 25°C		1.193	1.23	1.267
TJ = ±40 to +125°C		1.18	±	1.28
Efficiency (Vin = 12 V, ILoad = 3.0 A, Vout = 5.0 V)	η	±	77	±	%

NOTES: 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

MOTOROLA ANALOG IC DEVICE DATA	3

LM2576

DEVICE PARAMETERS

ELECTRICAL CHARACTERISTICS (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.)

				Characteristics			Symbol	Min	Typ	Max	Unit
ALL OUTPUT VOLTAGE VERSIONS
	Feedback Bias Current (Vout = 5.0 V [Adjustable Version Only])						Ib				nA
		TJ = 25°C						±	25	100
		TJ = ±40 to +125°C						±	±	200
	Oscillator Frequency [Note 3]						fosc				kHz
		TJ = 25°C						±	52	±
		TJ = 0 to +125°C						47	±	58
		TJ = ±40 to +125°C						42	±	63
	Saturation Voltage (Iout = 3.0 A [Note 4])						Vsat				V
		TJ = 25°C						±	1.5	1.8
		TJ = ±40 to +125°C						±	±	2.0
	Max Duty Cycle (ªonº) [Note 5]						DC	94	98	±	%
	Current Limit (Peak Current [Notes 3 and 4])						ICL				A
		TJ = 25°C						4.2	5.8	6.9
		TJ = ±40 to +125°C						3.5	±	7.5
	Output Leakage Current [Notes 6 and 7], TJ = 25°C						IL				mA
		Output = 0 V						±	0.8	2.0
		Output = ±1.0 V						±	6.0	20
	Quiescent Current [Note 6]						IQ				mA
		TJ = 25°C						±	5.0	9.0
		TJ = ±40 to +125°C						±	±	11
	Standby Quiescent Current						Istby				μA
					(ON/OFF Pin = 5.0 V (ªoffº))
		TJ = 25°C						±	80	200
		TJ = ±40 to +125°C						±	±	400
											V
	ON/OFF Pin Logic Input Level (Test Circuit Figure 15)
		Vout = 0 V					VIH
		TJ = 25°C						2.2	1.4	±
		TJ = ±40 to +125°C						2.4	±	±
		Vout = Nominal Output Voltage					VIL
		TJ = 25°C						±	1.2	1.0
		TJ = ±40 to +125°C						±	±	0.8
											μA
	ON/OFF Pin Input Current (Test Circuit Figure 15)
							I	±	15	30
		ON/OFF Pin = 5.0 V (ªoffº), T = 25°C
					J		IH
		ON/OFF Pin = 0 V (ªonº), T = 25°C					I	±	0	5.0
				J			IL

NOTES: 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 5.0 V versions, and +25 V for the 12 V and 15 V versions, to force the output transistor ªoffº.

7.Vin = 40 V.

4	MOTOROLA ANALOG IC DEVICE DATA

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

Figure 2. Normalized Output Voltage

Figure 3. Line Regulation

	1.0
(%)	0.8	Vin = 20 V
CHANGE	0.6	ILoad = 500 mA
		Normalized at TJ = 25°C
	0.4
VOLTAGE	0.2
	0
	±0.2
, OUTPUT
	±0.4
	±0.6
out	±0.8
V
	±1.0	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

	1.4
(%)	1.2	ILoad = 500 mA
CHANGE
	1.0	TJ = 25°C
	0.8
			3.3 V, 5.0 V and ADJ
VOLTAGE	0.6
	0.4
	0.2
OUTPUT							12 V and 15 V
	0
	±0.2
,
out	±0.4
V
	±0.6	5.0	10	15	20	25	30	35	40
	0
				Vin, INPUT VOLTAGE (V)

Figure 4. Dropout Voltage

Figure 5. Current Limit

	2.0
(V)		ILoad = 3.0 A
DIFFERENTIAL
	1.5
	1.0
± OUTPUT
				ILoad = 500 mA
	0.5
INPUT
							L1 = 150 μH
							Rind = 0.1	Ω
	0	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

	6.5
(A)	6.0						Vin = 25 V
CURRENT	5.5
, OUTPUT	5.0
O	4.5
I
	4.0
	±50	±25	0	25	50	75	100	125
			TJ, JUNCTION TEMPERATURE (°C)

Figure 6. Quiescent Current

Figure 7. Standby Quiescent Current

	20								A)
							Vout = 5.0 V		(μ
QUIESCENTCURRENT (mA)	18								QUIESCENT CURRENT
							Measured at
	16						Ground Pin
	14						TJ = 25°C
	12				ILoad = 3.0 A
	10
	8.0		ILoad = 200 mA
,									STANDBY,
Q
I	6.0
	4.0								stby
		5.0	10	15	20	25	30	35	I
	0								40
				Vin, INPUT VOLTAGE (V)

200
180	VON/OFF = 5.0 V
160
140
120		Vin = 40 V
100
80
60		Vin = 12 V
40
20
0
±50	±25	0	25	50	75	100	125
		TJ, JUNCTION TEMPERATURE (°C)

MOTOROLA ANALOG IC DEVICE DATA	5

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

Figure 8. Standby Quiescent Current

A)	200
(μ	180
CURRENT
	160
	140			TJ = 25°C
QUIESCENT	120
	100
	80
, STANDBY	60
	40
	20
stby
	0
I		5	10	15	20	25	30	35	40
	0
				Vin, INPUT VOLTAGE (V)

Figure 10. Oscillator Frequency

	8.0
(%)	6.0
	4.0	Vin = 12 V
FREQUENCY
		Normalized at
	2.0	25°C
	0
NORMALIZED	±2.0
	±4.0
	±6.0
	±8.0
	±10	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

Figure 9. Switch Saturation Voltage

	1.6
(V)	1.4
VOLTAGE	1.2	±40°C
	1.0
, SATURATION	0.8	25°C
	0.6	125°C
	0.4
sat
V	0.2
	0					2.5
	0	0.5	1.0	1.5	2.0		3.0

SWITCH CURRENT (A)

Figure 11. Minimum Operating Voltage

	5.0
	4.5				Adjustable Version Only
(V)	4.0
	3.5
VOLTAGE
	3.0
	2.5
, INPUT
	2.0
	1.5			Vout ' 1.23 V
in				ILoad = 500 mA
V	1.0
	0.5
	0	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

Figure 12. Feedback Pin Current

	100
(nA)	80				Adjustable Version Only
	60
CURRENT
	40
	20
PIN	0
,FEEDBACK	±20
	±40
	±60
b
I	±80
	±100	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

6	MOTOROLA ANALOG IC DEVICE DATA

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

Figure 13. Switching Waveforms

A	50 V
	0
	4.0 A
B	2.0 A
	0
	4.0 A
C	2.0 A
D	0
	5 μs/DIV

Vout = 15 V

A:Output Pin Voltage, 10 V/DIV

B:Inductor Current, 2.0 A/DIV

C:Inductor Current, 2.0 A/DIV, AC±Coupled

D:Output Ripple Voltage, 50mV/dDIV, AC±Coupled

Horizontal Time Base: 5 μs/DIV

Figure 14. Load Transient Response

100 mV
Output	0
Voltage
Change
± 100 mV
	3.0 A
Load	2.0 A
Current
	1.0 A
	0
	100 μs/DIV

MOTOROLA ANALOG IC DEVICE DATA	7

LM2576

Figure 15. Typical Test Circuit

Fixed Output Voltage Versions

					Feedback
		Vin	LM2576		4
						L1
		1	Fixed Output		Output	100 μH				Vout
					2
		3	Gnd	5	ON/OFF
7.0 V ± 40 V	Cin	μF				D1	C	μ
Unregulated	100						out		F
DC Input						MBR360	1000			Load

Cin	±	100 μF, 75 V, Aluminium Electrolytic
Cout ±		1000 μF, 25 V, Aluminium Electrolytic
D1	±	Schottky, MBR360
L1	±	100 μH, Pulse Eng. PE±92108
R1	±	2.0 k, 0.1%
R2	±	6.12 k, 0.1%

Adjustable Output Voltage Versions

Feedback

Vin

LM2576

4

L1

Vout

1

Adjustable

100 μH

Output

5,000 V

2

7.0 V ± 40 V

3

Gnd

5

ON/OFF

Cin

Cout

R2

Unregulated

μF

D1

μ

100

F

DC Input

1000

Load

MBR360

R1

Vout + Vref 1.0 )

R2

R1

R2 + R1

Vout

± 1.0

Vref

Where Vref = 1.23 V, R1

between 1.0 k and 5.0 k

PCB LAYOUT GUIDELINES

As in any switching regulator, the layout of the printed circuit board is very important. Rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electromagnetic interferences (EMI) and affect the desired operation. As indicated in the Figure 15, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible.

For best results, single±point grounding (as indicated) or ground plane construction should be used.

On the other hand, the PCB area connected to the Pin 2 (emitter of the internal switch) of the LM2576 should be kept to a minimum in order to minimize coupling to sensitive circuitry.

Another sensitive part of the circuit is the feedback. It is important to keep the sensitive feedback wiring short. To assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the LM2576 regulator.

8	MOTOROLA ANALOG IC DEVICE DATA

				LM2576
				PIN FUNCTION DESCRIPTION
Pin			Symbol	Description (Refer to Figure 1)
1	Vin			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).
2	Output			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.
3	Gnd			Circuit ground pin. See the information about the printed circuit board layout.
4	Feedback			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.
5				It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total
		ON/OFF
				input supply current to approximately 80 μA. 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 1.4 V or
				if this pin is left open, the regulator will be in the ªonº condition.
				DESIGN PROCEDURE

Buck Converter Basics

The LM2576 is a ªBuckº or Step±Down Converter which is the most elementary forward±mode converter. Its basic schematic can be seen in Figure 16.

The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is on, the input voltage is connected to the input of the inductor.

The output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation:

IL(on) +	Vin ± Vout ton
	L

During this ªonº period, energy is stored within the core material in the form of magnetic flux. If the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the ªoffº period.

	Figure 16. Basic Buck Converter
	Power	L
	Switch
V	D	Cout	R
in			Load

The next period is the ªoffº period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. The current now flows through the catch diode thus maintaining the load current loop. This removes the stored energy from the inductor. The inductor current during this time is:

IL(off) +	Vout ± VD toff
	L

This period ends when the power switch is once again turned on. Regulation of the converter is accomplished by varying the duty cycle of the power switch. It is possible to describe the duty cycle as follows:

d + tonT , where T is the period of switching.

For the buck converter with ideal components, the duty cycle can also be described as:

d + Vout Vin

Figure 17 shows the buck converter, idealized waveforms of the catch diode voltage and the inductor current.

Figure 17. Buck Converter Idealized Waveforms

Von(SW)

	Voltage	Power	Power	Power	Power
		Switch	Switch	Switch	Switch
	Diode
		Off	On	Off	On
		VD(FWD)
					Time

				Ipk
	Current				ILoad(AV)
	Inductor	Imin	Power		Power
		Diode		Diode
			Switch		Switch
					Time

MOTOROLA ANALOG IC DEVICE DATA	9