MOTOROLA LM2576 Technical data

现货库存、技术资料、百科信息、热点资讯，精彩尽在鼎好!

!    

Order this document by LM2576/D



   

The LM2576 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a step–down switching 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 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 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 is significantly higher in comparison with popular three–terminal linear regulators, 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 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 protection under fault conditions.

Features

• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions

• Adjustable Version Output Voltage Range, 1.23 to 37 V ±4% Maximum

Over Line and Load Conditions

• Guaranteed 3.0 A Output Current

• Wide Input Voltage Range

• Requires Only 4 External Components

• 52 kHz Fixed Frequency Internal Oscillator

• TTL Shutdown Capability , Low Power Standby Mode

• High Efficiency

• Uses Readily Available Standard Inductors

• 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

EASY SWITCHER

3.0 A STEP–DOWN

VOLTAGE REGULATOR

SEMICONDUCTOR

TECHNICAL DATA

T SUFFIX

PLASTIC PACKAGE

CASE 314D

Pin 1. V

2. Output

3. Ground

4. Feedback

5. ON

TV SUFFIX

PLASTIC PACKAGE

CASE 314B

Heatsink surface

connected to Pin 3.

D2T SUFFIX

PLASTIC PACKAGE

CASE 936A

(D2PAK)

Heatsink surface (shown as terminal 6 in case outline

DEVICE TYPE/NOMINAL OUTPUT VOLTAGE

LM2576–3.3 LM2576–5 LM2576–12 LM2576–15 LM2576–ADJ

ORDERING INFORMATION

Device

LM2576T–XX LM2576TV–XX TJ = –40° to +125°C LM2576D2T–XX

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

/OFF

drawing) is connected to Pin 3.

3.3 V

5.0 V 12 V 15 V

1.23 V to 37 V

Operating

Temperature Range

Package

Straight Lead

Vertical Mount

Surface Mount

MOTOROLA ANALOG IC DEVICE DATA

 Motorola, Inc. 1999 Rev 1, 07/1999

LM2576

Figure 1. Block Diagram and T ypical Application

T ypical Application (Fixed Output Voltage Versions)

Feedback

7.0 V – 40 V

Unregulated

DC Input

100

LM2576

3ON

Gnd

4 Output

/OFF5

Representative Block Diagram and T ypical Application

100

D1 1N5822

out

1000

5.0 V Regulated Output 3.0 A Load

Unregulated

DC Input

Feedback

Fixed Gain Error Amplifier

1.0 k 18 kHz

1.235 V Band–Gap Reference

Freq Shift

3.1 V Internal Regulator

Comparator

52 kHz

Oscillator

Current

Latch

Reset

Limit

/OFF

Driver

Thermal

Shutdown

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond

which damage to the device may occur.)

Rating

Maximum Supply Voltage V ON/OFF Pin Input Voltage – –0.3 V ≤ V ≤ +V Output Voltage to Ground (Steady–State) – –1.0 V Power Dissipation

Case 314B and 314D (TO–220, 5–Lead) P

Thermal Resistance, Junction–to–Ambient R Thermal Resistance, Junction–to–Case R

Case 936A (D2PAK) P

Thermal Resistance, Junction–to–Ambient R

Thermal Resistance, Junction–to–Case R Storage Temperature Range T Minimum ESD Rating (Human Body Model:

C = 100 pF, R = 1.5 kΩ) Lead Temperature (Soldering, 10 seconds) – 260 °C Maximum Junction Temperature T

NOTE: ESD data available upon request.

Symbol Value Unit

θJA θJC

stg

– 2.0 kV

45 V

Internally Limited W

65 °C/W

5.0 °C/W

Internally Limited W

70 °C/W

5.0 °C/W

–65 to +150 °C

150 °C

1.0 Amp Switch

/OFF

ON 5

Output 2

Gnd 3

Output

Voltage Versions

3.3 V

5.0 V 12 V 15 V

For adjustable version R1 = open, R2 = 0

1.7 k

3.1 k

8.84 k

11.3 k

Ω

out

Ω

)

(

Regulated

Output

out

Load

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

Operating Junction Temperature Range T Supply Voltage V

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

ELECTRICAL CHARACTERISTICS

the 12 V version, and Vin = 30 V for the 15 V version. I junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics

LM2576–3.3 ([Note 1] Test Circuit Figure 15)

Output Voltage (Vin = 12 V, I Output Voltage (6.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 3.168 3.3 3.432 TJ = –40 to +125°C 3.135 – 3.465

Efficiency (Vin = 12 V, I

LM2576–5 ([Note 1] Test Circuit Figure 15)

Output Voltage (Vin = 12 V, I Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 4.8 5.0 5.2 TJ = –40 to +125°C 4.75 – 5.25

Efficiency (Vin = 12 V, I

LM2576–12 ([Note 1] Test Circuit Figure 15)

Output Voltage (Vin = 25 V, I Output Voltage (15 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 11.52 12 12.48 TJ = –40 to +125°C 11.4 – 12.6

Efficiency (Vin = 15 V, I

LM2576–15 ([Note 1] Test Circuit Figure 15)

Output Voltage (Vin = 30 V, I Output Voltage (18 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 14.4 15 15.6 TJ = –40 to +125°C 14.25 – 15.75

Efficiency (Vin = 18 V, I

LM2576 ADJUSTABLE VERSION ([Note 1] Test Circuit Figure 15)

Feedback Voltage (Vin = 12 V, I Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ I

TJ = 25°C 1.193 1.23 1.267 TJ = –40 to +125°C 1.18 – 1.28

Efficiency (Vin = 12 V, I

NOTES: 1. External components such as the catch diode, inductor, input and output capacitors can af fect switching regulator system performance. When the

LM2576 is used as shown in the

2.Tested junction temperature range for the LM2576: T

Load

= 3.0 A) η – 75 – %

Load

= 3.0 A) η – 77 – %

Load

= 3.0 A) η – 88 – %

Load

= 3.0 A) η – 88 – %

Load

= 3.0 A, V

Load

(Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for

= 0.5 A, TJ = 25°C) V

Load

= 0.5 A, TJ = 25°C) V

Load

= 0.5 A, TJ = 25°C) V

Load

= 0.5 A, TJ = 25°C) V

Load

= 0.5 A, V

= 5.0 V) η – 77 – %

out

Figure 15 test circuit, system performance will be as shown in system parameters section

Symbol Value Unit

= 500 mA. For typical values TJ = 25°C, for min/max values TJ is the operating

Load

≤ 3.0 A) V

= 5.0 V, TJ = 25°C) V

out

≤ 3.0 A, V

Load

low

–40 to +125 °C

= 5.0 V) V

out

= –40°C T

40 V

Symbol Min Typ Max Unit

3.234 3.3 3.366 V

4.9 5.0 5.1 V

11.76 12 12.24 V

14.7 15 15.3 V

1.217 1.23 1.243 V

high

out out

= +125°C

MOTOROLA ANALOG IC DEVICE DATA

LM2576

DEVICE PARAMETERS

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, V

the 12 V version, and Vin = 30 V for the 15 V version. I junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics

ALL OUTPUT VOLTAGE VERSIONS

Feedback Bias Current (V

TJ = 25°C – 25 100 TJ = –40 to +125°C – – 200

Oscillator Frequency [Note 3] f

TJ = 25°C – 52 – TJ = 0 to +125°C 47 – 58 TJ = –40 to +125°C 42 – 63

Saturation Voltage (I

TJ = 25°C – 1.5 1.8 TJ = –40 to +125°C – – 2.0

Max Duty Cycle (“on”) [Note 5] DC 94 98 – % Current Limit (Peak Current [Notes 3 and 4]) I

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 I

Output = 0 V – 0.8 2.0 Output = –1.0 V – 6.0 20

Quiescent Current [Note 6] I

TJ = 25°C – 5.0 9.0 TJ = –40 to +125°C – – 11

Standby Quiescent Current (ON/OFF Pin = 5.0 V (“off”)) I

TJ = 25°C – 80 200 TJ = –40 to +125°C – – 400

ON/OFF Pin Logic Input Level (Test Circuit Figure 15) V

= 0 V V

out

TJ = 25°C 2.2 1.4 – TJ = –40 to +125°C 2.4 – –

= Nominal Output Voltage V

out

TJ = 25°C – 1.2 1.0 TJ = –40 to +125°C – – 0.8

ON/OFF Pin Input Current (Test Circuit Figure 15) µA

ON/OFF Pin = 5.0 V (“off”), TJ = 25°C I ON/OFF Pin = 0 V (“on”), TJ = 25°C I

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 “off”.

7.Vin = 40 V.

out

= 5.0 V [Adjustable Version Only]) I

out

= 3.0 A [Note 4]) V

= 500 mA. For typical values TJ = 25°C, for min/max values TJ is the operating

Load

= 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for

Symbol Min Typ Max Unit

osc

sat

stby

– 15 30 – 0 5.0

kHz

µA

MOTOROLA ANALOG IC DEVICE DATA

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

1.0

Figure 2. Normalized Output Voltage

Vin = 20 V

0.8 I

= 500 mA

Load

0.6

Normalized at TJ = 25

0.4

0.2

0 –0.2 –0.4

–0.6

, OUTPUT VOLTAGE CHANGE (%)

out

–0.8

–1.0

2.0 I

Load

1.5

1.4

1.2

= 500 mA

Load

TJ = 25

, OUTPUT VOLTAGE CHANGE (%), STANDBY QUIESCENT CURRENT ( V

–0.2

out

–0.4 –0.6

1.0

0.8

0.6

0.4

0.2

3.3 V, 5.0 V and ADJ

Vin, INPUT VOLTAGE (V)

12 V and 15 V

TJ, JUNCTION TEMPERATURE (°C)

1251007550250–25–50 403530252015105.00

Figure 4. Dropout Voltage Figure 5. Current Limit

6.5

Figure 3. Line Regulation

= 3.0 A

6.0

Vin = 25 V

INPUT – OUTPUT DIFFERENTIAL (V)

, QUIESCENT CURRENT (mA)

1.0

0.5

20 18 16 14 12 10

8.0

6.0

4.0

5.5

, OUTPUT CURRENT (A)

5.0

4.5

4.0

TJ, JUNCTION TEMPERATURE (°C)

= 500 mA

Load

L1 = 150 µH R

TJ, JUNCTION TEMPERATURE (°C)

ind

= 0.1

Ω

1251007550250–25–50 1251007550250–25–50

Figure 6. Quiescent Current Figure 7. Standby Quiescent Current

200

stby

180 160 140 120 100

80 60 40 20

= 5.0 V

ON/OFF

Vin = 40 V

Vin = 12 V

TJ, JUNCTION TEMPERATURE (°C)

= 200 mA

Load

Vin, INPUT VOLTAGE (V)

Load

= 3.0 A

= 5.0 V

out

Measured at Ground Pin

TJ = 25

403530252015105.00 1251007550250–25–50

MOTOROLA ANALOG IC DEVICE DATA

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

A)I

, STANDBY QUIESCENT CURRENT (

stby

NORMALIZED FREQUENCY (%)

200 180 160 140

120 100

80 60

40 20

8.0

6.0

4.0

2.0

–2.0 –4.0 –6.0

–8.0

–10

Figure 8. Standby Quiescent Current

TJ = 25°C

Vin, INPUT VOLTAGE (V)

Figure 10. Oscillator Frequency Figure 11. Minimum Operating Voltage

Vin = 12 V Normalized at

TJ, JUNCTION TEMPERATURE (°C)

1.6

Figure 9. Switch Saturation Voltage

1.4

1.2 –40°C

1.0

0.8

25°C

0.6 125°C

, SATURATION VOLTAGE (V)

0.4

sat

0.2

35 2.5

40302520151050 0 0.5 1.0 1.5 2.0 3.0

1251007550250–25–50 1251007550250–25–50

5.0

4.5

4.0

3.5

3.0

2.5

2.0

, INPUT VOLTAGE (V)

1.5

1.0

0.5

SWITCH CURRENT (A)

Adjustable Version Only

' 1.23 V

out

= 500 mA

Load

TJ, JUNCTION TEMPERATURE (°C)

100

Figure 12. Feedback Pin Current

80 60 40

0 –20 –40 –60

, FEEDBACK PIN CURRENT (nA)

–80

–100

TJ, JUNCTION TEMPERATURE (

Adjustable Version Only

1251007550250–25–50

MOTOROLA ANALOG IC DEVICE DATA

LM2576

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15)

50 V

Figure 13. Switching Waveforms Figure 14. Load Transient Response

4.0 A

2.0 A 0

4.0 A

2.0 A

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

Output

Voltage

Change

– 100 mV

Load

Current

100 mV

3.0 A

2.0 A

1.0 A 0

100

s/DIV5 µs/DIV

MOTOROLA ANALOG IC DEVICE DATA

7.0 V – 40 V Unregulated

DC Input

LM2576

Figure 15. T ypical Test Circuit Fixed Output Voltage Versions

Feedback

LM2576

Fixed Output

100

Cin– 100 µF, 75 V, Aluminium Electrolytic C

– 1000 µF, 25 V, Aluminium Electrolytic

out

D1 – Schottky , MBR360 L1 – 100 µH, Pulse Eng. PE–92108 R1 – 2.0 k, 0.1% R2 – 6.12 k, 0.1%

Output

/OFFGnd

53ON

100

D1 MBR360

out

1000

out

Load

7.0 V – 40 V Unregulated

DC Input

100

Adjustable Output Voltage Versions

Feedback

LM2576

Adjustable

Output

/OFFGnd

53ON

out

ref

R2+R1

Where V between 1.0 k and 5.0 k

= 1.23 V, R1

ref

out

ref

1.0

100

D1 MBR360

)

–1.0

out

1000

out

5,000 V

Load

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.

MOTOROLA ANALOG IC DEVICE DATA

LM2576

PIN FUNCTION DESCRIPTION

Pin Symbol Description (Refer to Figure 1)

1 V

2 Output This is the emitter of the internal switch. The saturation voltage V

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

5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total

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

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.

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.

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 “on” condition.

Figure 1).

of this output switch is typically 1.5 V.

sat

DESIGN PROCEDURE

Buck Converter Basics

The LM2576 is a “Buck” 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:

L(on)

Vin–V

out

During this “on” 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 “off” period.

Figure 16. Basic Buck Converter

Power

Switch

out

Load

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:

, where T is the period of switching.

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

out

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

Figure 17. Buck Converter Idealized Waveforms

on(SW)

Power Switch

Off

Diode VoltageInductor Current

VD(FWD)

Power Switch

Off

Power

Switch

Time

The next period is the “off” 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:

L(off)

out

–V

off

MOTOROLA ANALOG IC DEVICE DATA

min

Diode Diode

Power

Switch

(AV)

Load

Power Switch

Time

+ 19 hidden pages