Motorola LM2574N Datasheet

 

   

Order this document by LM2574/D



  

The LM2574 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 0.5 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 LM2574 are offered by several different
inductor manufacturers.

Since the LM2574 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 most cases, the power
dissipated by the LM2574 regulator is so low, that the copper traces on the
printed circuit board are normally the only heatsink needed and no additional
heatsinking is required.

The LM2574 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 60 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% max over

Line and Load Conditions

• Guaranteed 0.5 A Output Current

• Wide Input Voltage Range: 4.75 to 40 V

• 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

EASY SWITCHER

0.5 A STEP–DOWN

VOLTAGE REGULATOR

SEMICONDUCTOR

TECHNICAL DATA

8

1

N SUFFIX

PLASTIC PACKAGE

CASE 626

PIN CONNECTIONS

1

FB

2

Sig Gnd

/OFF

3
4

(Top View)

ON
Pwr Gnd

* No internal connection, but should be soldered to

* PC board for best heat transfer.

8
7
6
5

*
Output

*
V

in

Applications

• Simple and High–Efficiency Step–Down (Buck) Regulators

• Efficient Pre–regulator for Linear Regulators

• On–Card Switching Regulators

• Positive to Negative Converters (Buck–Boost)

• Negative Step–Up Converters

• Power Supply for Battery Chargers

This document contains information on a new product. Specifications and information herein
are subject to change without notice.

DEVICE TYPE/NOMINAL OUTPUT VOLTAGE

LM2574–3.3
LM2574–5
LM2574–12
LM2574–15
LM2574–ADJ

ORDERING INFORMATION

Operating

Device

LM2574N–XX TA = –40° to +125°C DIP–8

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

 Motorola, Inc. 1997 Rev 0

Temperature Range

3.3 V

5.0 V
12 V
15 V

1.23 V to 37 V

Package

7.0 – 40 V

Unregulated

DC Input

LM2574

Figure 1. Block Diagram and T ypical Application

T ypical Application (Fixed Output Voltage Versions)

Feedback
1

Output
7

22

+V

in

5

C

in

µ

F

2

Sig
Gnd

LM2574

4ON/OFF3

Pwr
Gnd

Representative Block Diagram and T ypical Application

L1

µ

330

D1
1N5819

H

C

out

µ

220

5.0 V Regulated
Output 0.5 A Load

F

+V

Unregulated

DC Input

C

in

in

5

1

Feedback

Sig Gnd

2

R2

Fixed Gain
Error Amplifier

R1

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

ON

Limit

/OFF

Driver

1.0 Amp
Switch

Thermal

Shutdown

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond which

damage to the device may occur).

Rating Symbol Value Unit

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 P

Thermal Resistance, Junction–to–Ambient R

Thermal Resistance, Junction–to–Case R
Storage Temperature Range T
Minimum ESD Rating – 2.0 kV

(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.

in

D

θJA
θJC

stg

J

45 V

in

Internally Limited W

100 °C/W

5.0 °C/W

–65°C to +150°C °C

150 °C

V

/OFF

ON
3

Output
7

Pwr Gnd
4

Output

Voltage Versions

3.3 V

5.0 V
12 V
15 V

For adjustable version
R1 = open, R2 = 0

L1

D1

(

1.7 k

3.1 k

8.84 k

11.3 k

Ω

C

out

R2

Ω

)

V

out

Load

2

MOTOROLA ANALOG IC DEVICE DATA

LM2574

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 16)

ELECTRICAL CHARACTERISTICS

Vin = 25 V for the 12 V version, Vin = 30 V for the 15 V version. I
operating junction temperature range that applies [Note 2], unless otherwise noted).

Characteristic

LM2574–3.3 ([Note 1] Test Circuit Figure 16)

Output Voltage (Vin = 12 V, I
Output Voltage (4.75 V ≤ Vin ≤ 40 V, 0.1 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

LM2574–5 ([Note 1] Test Circuit Figure 16)

Output Voltage (Vin = 12 V, I
Output Voltage (7.0 V ≤ Vin ≤ 40 V, 0.1 A ≤ I

T

= 25°C

J

T

= –40 to +125°C

J

Efficiency (Vin = 12 V, I

LM2574–12 ([Note 1] Test Circuit Figure 16)

Output Voltage (Vin = 25 V, I
Output Voltage (15 V ≤ Vin ≤ 40 V, 0.1 A ≤ I

T

= 25°C

J

T

= –40 to +125°C

J

Efficiency (Vin = 15 V, I

LM2574–15 ([Note 1] Test Circuit Figure 16)

Output Voltage (Vin = 30 V, I
Output Voltage (18 V < Vin < 40 V, 0.1 A < I

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

Efficiency (Vin = 18 V, I

LM2574 ADJUSTABLE VERSION ([Note 1] Test Circuit Figure 16)

Feedback Voltage Vin = 12 V, I
Feedback Voltage 7.0 V ≤ Vin ≤ 40 V, 0.1 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 the switching regulator system

performance. When the LM2574 is used as shown in the Figure 16 test circuit, the system performance will be as
shown in the system parameters section of the Electrical Characteristics.

2.Tested junction temperature range for the LM2574: T

Load

= 0.5 A) η – 72 – %

Load

Load

= 0.5 A) η – 77 – %

Load

Load

= 0.5 A) η – 88 – %

Load

Load

= 0.5 A) η – 88 – %

Load

Load

= 0.5 A, V

Load

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

= 100 mA, TJ = 25°C) V

Load

= 100 mA, TJ = 25°C) V

Load

= 100 mA, TJ = 25°C) V

Load

= 100 mA, TJ = 25°C) V

Load

= 100 mA, V

Load

= 5.0 V) η – 77 – %

out

Symbol Value Unit

J

in

≤ 0.5 A) V

≤ 0.5 A) V

≤ 0.5 A) V

< 0.5 A) V

= 5.0 V, TJ = 25°C V

out

≤ 0.5 A, V

= –40°C T

low

–40 to +125 °C

40 V

= 100 mA. For typical values TJ = 25°C, for min/max values TJ is the

Load

Symbol Min Typ Max Unit

= 5.0 V V

out

= +125°C

high

out
out

out
out

out
out

out
out

FB

FBT

3.234 3.3 3.366 V

4.9 5.0 5.1 V

4.8 5.0 5.2

4.75 5.25

11.76 10 12.24 V

11.52 12 12.48

11.4 – 12.6

14.7 15 15.3 V

1.217 1.23 1.243 V

V

V

V

V

V

MOTOROLA ANALOG IC DEVICE DATA

3

LM2574

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 16)

ELECTRICAL CHARACTERISTICS

Vin = 25 V for the 12 V version, Vin = 30 V for the 15 V version. I
operating junction temperature range that applies [Note 2], unless otherwise noted).

Characteristic UnitMaxTypMinSymbol

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 52 58
TJ = –40 to +125°C 42 – 63

Saturation Voltage (I

TJ = 25°C – 1.0 1.2

TJ = –40 to +125°C – – 1.4
Max Duty Cycle (“on”) [Note 5] DC 93 98 – %
Current Limit Peak Current (Notes 3 and 4) I

TJ = 25°C 0.7 1.0 1.6

TJ = –40 to +125°C 0.65 – 1.8
Output Leakage Current (Notes 6 and 7), TJ = 25°C I

Output = 0 V – 0.6 2.0

Output = – 1.0 V – 10 30
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 – 60 200

TJ = –40 to +125°C – – 400
ON/OFF Pin Logic Input Level V

V

= 0 V V

out

TJ = 25°C 2.2 1.4 –

TJ = –40 to +125°C 2.4 – –

Nominal Output Voltage V

TJ = 25°C – 1.2 1.0

TJ = –40 to +125°C – – 0.8
ON/OFF Pin Input Current µA

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

ON/OFF Pin = 0 V (“on”), TJ = 25°C I

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

performance. When the LM2574 is used as shown in the Figure 16 test circuit, the system performance will be as
shown in the system parameters section of the Electrical Characteristics.

2.Tested junction temperature range for the LM2574: T

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 power 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 the 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.

= 5.0 V (Adjustable Version Only) I

out

= 0.5 A, [Note 4]) V

out

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

= 100 mA. For typical values TJ = 25°C, for min/max values TJ is the

Load

b

O

sat

CL

L

Q

stby

IH

IL

– 15 30
– 0 5.0

= –40°C T

low

high

IH

IL

= +125°C

nA

kHz

V

A

mA

mA

µA

4

MOTOROLA ANALOG IC DEVICE DATA

LM2574

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16)

1.0

Figure 2. Normalized Output Voltage

Vin = 20 V

0.8
I

= 100 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

V

–1.0

2.0
L = 300 µH

1.5

1.4

1.2

I

= 100 mA

Load

°

C

TJ = 25

°

C

TJ, JUNCTION TEMPERATURE (°C)

1251007560250–25–50 403530252015105.00

1.0

0.8

0.6

0.4

0.2
0

–0.2

, OUTPUT VOLTAGE CHANGE (%)

out

–0.4

V

–0.6

3.3 V, 5.0 V and ADJ

12 V and 15 V

Vin, INPUT VOLTAGE (V)

Figure 4. Dropout Voltage Figure 5. Current Limit

1.4

1.3

I

Figure 3. Line Regulation

Load

= 500 mA

1.2

Vin = 25 V

INPUT – OUTPUT DIFFERENTIAL (V)

, QUIESCENT CURRENT (mA)

Q

I

1.0

0.5

20
18
16
14
12
10

8.0

6.0

4.0

1.1

, OUTPUT CURRENT (A)

O

I

1.0

0.9

0.8

0.7

TJ, JUNCTION TEMPERATURE (°C)

I

= 100 mA

Load

0

TJ, JUNCTION TEMPERATURE (°C)

1251007560250–25–50 1251007560250–25–50

Figure 6. Quiescent Current Figure 7. Standby Quiescent Current

200

µ

, STANDBY QUIESCENT CURRENT ( A)

stby

I

180
160
140
120
100

80
60
40
20

V

= 5.0 V

ON

/OFF

Vin = 40 V

Vin = 12 V

0

TJ, JUNCTION TEMPERATURE (°C)

I

Load

I

= 100 mA

Load

Vin, INPUT VOLTAGE (V)

= 500 A

V

= 5.0 V

out

Measured at
Ground Pin

°

C

TJ = 25

403530252015105.00 1251007560250–25–50

MOTOROLA ANALOG IC DEVICE DATA

5

LM2574

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16) (continued)

NORMALIZED FREQUENCY (%)

, INPUT VOLTAGE (V)V

in

8.0

6.0

4.0

2.0

–2.0
–4.0
–6.0
–8.0

10

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

Vin = 12 V
Normalized at 25

0

Figure 8. Oscillator Frequency

°

C

TJ, JUNCTION TEMPERATURE (°C)

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

, SATURATION VOLTAGE (V)I

0.5

sat

V

0.4

1251007550250–25–50 0 0.1 0.2 0.3 0.4 0.5

0.3

Figure 9. Switch Saturation Voltage

–40°C

25°C

125°C

SWITCH CURRENT (A)

Figure 10. Minimum Operating V oltage Figure 11. Feedback Pin Current

100

–20
–40
–60

, FEEDBACK PIN CURRENT (nA)

FB

–80

–100

80
60
40
20

0

TJ, JUNCTION TEMPERATURE (

0

Vin = 1.23 V
I

= 100 mA

Load

TJ, JUNCTION TEMPERATURE (

Adjustable Version Only

°

C)

1251007550250–25–50 1251007550250–25–50

Adjustable Version Only

°

C)

Figure 12. Continuous Mode Switching Waveforms

V

= 5.0 V, 500 mA Load Current, L = 330 µH

out

20 V

A

10 V

0

0.6 A

0.4 A

B

0.2 A
0

20 mV

C

AC

5

µ

s/DIV

A: Output Pin Voltage, 10 V/DIV.
B: Inductor Current, 0.2 A/DIV .
C: Output Ripple Voltage, 20 mV/DIV, AC–Coupled

6

Figure 13. Discontinuous Mode Switching Waveforms

V

= 5.0 V, 100 mA Load Current, L = 100 µH

out

20 V

A

10 V

0

0.6 A

B

0.4 A

0.2 A
0

20 mV

C

AC

5

µ

s/DIV

A: Output Pin Voltage, 10 V/DIV.
B: Inductor Current, 0.2 A/DIV .
C: Output Ripple Voltage, 20 mV/DIV, AC–Coupled

MOTOROLA ANALOG IC DEVICE DATA

LM2574

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 16) (continued)

Figure 14. 500 mA Load Transient Response for

Continuous Mode Operation, L = 330 µH, C

50 mV

A

AC

500 mA

B

0

A: Output Voltage, 50 mV/DIV, AC Coupled

B: 100 mA to 500 mA Load Pulse

= 300 µF

out

Figure 15. 250 mA Load Transient Response for

Discontinuous Mode Operation, L = 68 µH, C

50 mV

A

AC

200 mA

B

100 mA

0

200

µ

s/DIV200 µs/DIV

A: Output Voltage, 50 mV/DIV, AC Coupled

B: 50 mA to 250 mA Load Pulse

= 470 µF

out

MOTOROLA ANALOG IC DEVICE DATA

7

7.0 – 40 V

Unregulated

DC Input

7.0 V – 40 V
Unregulated

DC Input

Figure 16. T est Circuit and Layout Guidelines

Fixed Output Voltage Versions

V

in
1

C

in

22

µ

F

Cin–22 µF, 60 V, Aluminium Electrolytic
C

– 220 µF, 25 V, Aluminium Electrolytic

out

D1 – Schottky, 1N5819
L1 – 330 µH, (For 5.0 Vin, 3.3 V
R1 – 2.0 k, 0.1%
R2 – 6.12 k, 0.1%

LM2574

Fixed Output

2 Sig

Gnd

Adjustable Output Voltage Versions

V

C
22

in

1

in

µ

F

LM2574

Adjustable

2 Sig

Gnd

34ON/OFFPwr

Gnd

LM2574

Feedback

1

Output
7

/OFFPwr

34ON

Gnd

, use 100 µH)

out

Feedback

1

Output

7

L1

µ

H

330

D1
1N5819

L1

µ

H

330

D1
1N5819

C

out

220

V

out

C

out

220

µ

F

Load

µ

F

V

out

5.0 V

R2

6.12 k
Load

R1

2.0 k

V

+

V

out

ref

R2+R1

ǒ

Where V
between 1.0 k

= 1.23 V, R1

ref

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 16, 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.

ǒ

1.0

V

out

V

ref

Ω

and 5.0 k

R2

Ǔ

)

R1

–1.0

Ǔ

Ω

On the other hand, the PCB area connected to the Pin 7
(emitter of the internal switch) of the LM2574 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
LM2574 regulator.

8

MOTOROLA ANALOG IC DEVICE DATA