Datasheet LM2575T, LM2575TV, LM2575D2T Datasheet (Motorola)

Device

Operating

Temperature Range

Package



EASY SWITCHER

1.0 A STEP–DOWN

VOLTAGE REGULATOR

ORDERING INFORMATION

LM2575T–**
LM2575TV–** T

J

= –40° to +125°C

Straight Lead

Vertical Mount

DEVICE TYPE/NOMINAL OUTPUT VOLTAGE

LM2575–3.3
LM2575–5
LM2575–12
LM2575–15
LM2575–Adj

3.3 V

5.0 V
12 V
15 V

1.23 V to 37 V

D2T SUFFIX

PLASTIC PACKAGE

CASE 936A

(D

2

PAK)

1

5

Order this document by LM2575/D

T SUFFIX

PLASTIC PACKAGE

CASE 314D

TV SUFFIX

PLASTIC PACKAGE

CASE 314B

Pin 1. V

in

2. Output

3. Ground

4. Feedback

5. ON

/OFF

LM2575D2T–**

Surface Mount

1

5

1

5

Heatsink surface (shown as terminal 6 in case outline

drawing) is connected to Pin 3.

Heatsink surface

connected to Pin 3.

** = Voltage Option, ie. 3.3, 5.0, 12, 15 V and

** =\Adjustable Output.

SEMICONDUCTOR

TECHNICAL DATA

1

MOTOROLA ANALOG IC DEVICE DATA

 

   
  

The LM2575 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 1.0 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 optimised for use with the LM2575 are offered by several different
inductor manufacturers.

Since the LM2575 converter is a switch–mode power supply, its ef ficiency
is significantly higher in comparison with popular three–terminal linear
regulators, especially with higher input voltages. In many cases, the power
dissipated by the LM2575 regulator is so low, that no heatsink is required or
its size could be reduced dramatically.

The LM2575 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 of 1.23 V to 37 V ±4%

Maximum Over Line and Load Conditions

• Guaranteed 1.0 A Output Current

• Wide Input Voltage Range: 4.75 V 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

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.

 Motorola, Inc. 1997 Rev 1

LM2575

2

MOTOROLA ANALOG IC DEVICE DATA

Figure 1. Block Diagram and Typical Application

7.0 V – 40 V

Unregulated

DC Input

L1

330

µ

H

Gnd

+V

in

1

C

in

100 µF

3ON

/OFF5

Output
2

Feedback
4

D1
1N5819

C

out

330 µF

Typical Application (Fixed Output Voltage Versions)

Representative Block Diagram and Typical Application

Unregulated

DC Input

+V

in

1

C

out

Feedback

4

C

in

L1

D1

R2

R1

1.0 k
Output

2
Gnd

3

ON

/OFF

5

Reset

Latch

Thermal

Shutdown

52 kHz

Oscillator

1.235 V
Band–Gap
Reference

Freq
Shift

18 kHz

Comparator

Fixed Gain
Error Amplifier

Current

Limit

Driver

1.0 Amp
Switch

ON

/OFF

3.1 V Internal
Regulator

Regulated

Output

V

out

Load

Output

Voltage Versions

3.3 V

5.0 V
12 V
15 V

R2

(

Ω

)

1.7 k

3.1 k

8.84 k

11.3 k

For adjustable version
R1 = open, R2 = 0

Ω

LM2575

5.0 V Regulated
Output 1.0 A Load

This device contains 162 active transistors.

ABSOLUTE MAXIMUM RATINGS (Absolute Maximum Ratings indicate limits beyond

which damage to the device may occur.)

Rating

Symbol Value Unit

Maximum Supply Voltage V

in

45 V

ON/OFF Pin Input Voltage – –0.3 V ≤ V ≤ +V

in

V
Output Voltage to Ground (Steady–State) – –1.0 V
Power Dissipation

Case 314B and 314D (TO–220, 5–Lead) P

D

Internally Limited W

Thermal Resistance, Junction–to–Ambient R

θ

JA

65 °C/W

Thermal Resistance, Junction–to–Case R

θ

JC

5.0 °C/W

Case 936A (D2PAK) P

D

Internally Limited W

Thermal Resistance, Junction–to–Ambient

(Figure 34)

R

θ

JA

70 °C/W

Thermal Resistance, Junction–to–Case R

θ

JC

5.0 °C/W

Storage Temperature Range T

stg

–65 to +150 °C

Minimum ESD Rating (Human Body Model: C

= 100 pF, R = 1.5 kΩ)

– 3.0 kV

Lead Temperature (Soldering, 10 s) – 260 ° C
Maximum Junction Temperature T

J

150 ° C

NOTE: ESD data available upon request.

LM2575

3

MOTOROLA ANALOG IC DEVICE DATA

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 T

J

–40 to +125 °C

Supply Voltage V

in

40 V

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 14)

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 V

in

= 30 V for the 15 V version. I

Load

= 200 mA. For typical values T

J

= 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

LM2575–3.3 ([Note 1] Test Circuit Figure 14)

Output Voltage (Vin = 12 V, I

Load

= 0.2 A, T

J

= 25°C) V

out

3.234 3.3 3.366 V

Output Voltage (4.75 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

Load

≤ 1.0 A) V

out

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

Efficiency (V

in

= 12 V , I

Load

= 1.0 A) η – 75 – %

LM2575–5 ([Note 1] Test Circuit Figure 14)

Output Voltage (Vin = 12 V, I

Load

= 0.2 A, TJ = 25°C) V

out

4.9 5.0 5.1 V

Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

Load

≤ 1.0 A) V

out

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

Efficiency (Vin = 12 V, I

Load

= 1.0 A) η – 77 – %

LM2575–12 ([Note 1] Test Circuit Figure 14)

Output Voltage (Vin = 25 V, I

Load

= 0.2 A, TJ = 25°C) V

out

11.76 12 12.24 V

Output Voltage (15 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

Load

≤ 1.0 A) V

out

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

Efficiency (Vin = 15V, I

Load

= 1.0 A) η – 88 – %

LM2575–15 ([Note 1] Test Circuit Figure 14)

Output Voltage (V

in

= 30 V , I

Load

= 0.2 A, TJ = 25°C) V

out

14.7 15 15.3 V

Output Voltage (18 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

Load

≤ 1.0 A) V

out

V
TJ = 25°C 14.4 15 15.6
T

J

= –40 to +125°C 14.25 – 15.75

Efficiency (Vin = 18 V, I

Load

= 1.0 A) η – 88 – %

LM2575 ADJUSTABLE VERSION ([Note 1] Test Circuit Figure 14)

Feedback Voltage (V

in

= 12 V , I

Load

= 0.2 A, V

out

= 5.0 V , TJ = 25°C) V

FB

1.217 1.23 1.243 V

Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ I

Load

≤ 1.0 A, V

out

= 5.0 V) V

FB

V
TJ = 25°C 1.193 1.23 1.267
T

J

= –40 to +125°C 1.18 – 1.28

Efficiency (V

in

= 12 V , I

Load

= 1.0 A, V

out

= 5.0 V) η – 77 – %

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

LM2575 is used as shown in the

Figure 14 test circuit, system performance will be as shown in system parameters section

.

2.Tested junction temperature range for the LM2575: T

low

= –40°C T

high

= +125°C

LM2575

4

MOTOROLA ANALOG IC DEVICE DATA

DEVICE PARAMETERS

ELECTRICAL CHARACTERISTICS (Unless otherwise specified, V

in

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

the 12 V version, and V

in

= 30 V for the 15 V version. I

Load

= 200 mA. For typical values T

J

= 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 (V

out

= 5.0 V [Adjustable Version Only]) I

b

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

Oscillator Frequency [Note 3] f

osc

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

Saturation Voltage (I

out

= 1.0 A [Note 4]) V

sat

V
TJ = 25°C – 1.0 1.2
TJ = –40 to +125°C – – 1.3

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

CL

A
TJ = 25°C 1.7 2.3 3.0
TJ = –40 to +125°C 1.4 – 3.2

Output Leakage Current [Notes 6 and 7], TJ = 25°C I

L

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

Quiescent Current [Note 6] I

Q

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

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

stby

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

ON/OFF Pin Logic Input Level (Test Circuit Figure 14) V

V

out

= 0 V V

IH

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

V

out

= Nominal Output Voltage V

IL

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

ON/OFF Pin Input Current (Test Circuit Figure 14) µA

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

IH

– 15 30

ON/OFF Pin = 0 V (“on”), TJ = 25°C I

IL

– 0 5.0

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.V

in

= 40 V.

LM2575

5

MOTOROLA ANALOG IC DEVICE DATA

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 14)

V

out

, OUTPUT VOLTAGE CHANGE (%)

0

20

–50

3.0

0

–50

2.0

0

1.2

–50

I

Q

, QUIESCENT CURRENT (mA)

Vin, INPUT VOLTAGE (V)

I

O

, OUTPUT CURRENT (A)

TJ, JUNCTION TEMPERATURE (°C)

V

in

, INPUT VOLTAGE (V)

INPUT–OUTPUT DIFFERENTIAL (V)

TJ, JUNCTION TEMPERATURE (°C)

V

sat

, SATURATION VOLTAGE (V)

SWITCH CURRENT (A)

V

out

, OUTPUT VOLTAGE CHANGE (%)

Figure 2. Normalized Output Voltage

TJ, JUNCTION TEMPERATURE (°C)

Figure 3. Line Regulation

Vin = 20 V
I

Load

= 200 mA
Normalized at
T

J

= 25°C

Figure 4. Switch Saturation Voltage Figure 5. Current Limit

Figure 6. Dropout Voltage Figure 7. Quiescent Current

I

Load

= 200 mA

T

J

= 25°C

3.3 V, 5.0 V and Adj

12 V and 15 V

25°C

Vin = 25 V

V

out

= 5.0 V
Measured at
Ground Pin
T

J

= 25°C

I

Load

= 200 mA

I

Load

= 1.0 A

∆

V

out

= 5%

R

ind

= 0.2

Ω

125°C

–40°C

5.0–25 100 201525 257550 3530 40100 125

0.8

0.4

0.4

0

0

–0.2

–0.4

0.6

0.2

1.00.6

0.2

–0.2

–0.6

2.5

1.5

0.5

0

2.0

1.0

14

10

6.0

4.0

18

12

8.0

16

1.1

0.9

0.7

0.5

1.0

0.8

0.6

1.2

0.8

0.4

1.0

0.6

1.8

1.4

1.6

0.4
–250.1 00.2 250.3 500.4 750.5 1000.6 1250.7

5.0–25 100 1525 2050 2575 30100 35125

0.8 0.9 1.0

40

I

Load

= 200 mA

I

Load

= 1.0 A

LM2575

6

MOTOROLA ANALOG IC DEVICE DATA

OUTPUT
VOLTAGE
(PIN 2)

OUTPUT
CURRENT
(PIN 2)

INDUCTOR

OUTPUT
RIPPLE
VOLTAGE

V

out

, OUTPUT VOL TAGE

I

stby

, STANDBY QUIESCENT CURRENT ( A)

µ

100

–50

–50

10 V

–50

0

100

µ

s/DIV

I

FB

, FEEDBACK PIN CURRENT (nA)

TJ, JUNCTION TEMPERATURE (°C)

T

J

, JUNCTION TEMPERATURE (°C)

5.0

µ

s/DIV

NORMALIZED FREQUENCY (%)

TJ, JUNCTION TEMPERATURE (°C)

I

stby

, STANDBY QUIESCENT CURRENT ( A)

µ

Figure 8. Standby Quiescent Current

Vin, INPUT VOLTAGE (V)

Figure 9. Standby Quiescent Current

Figure 10. Oscillator Frequency Figure 11. Feedback Pin Current

Figure 12. Switching Waveforms Figure 13. Load Transient Response

Vin = 12 V
V

ON/OFF

= 5.0 V

TJ = 25°C

–1001.0 A

1.0

40

0

2.0

0.5

20

1.0 A

0

120

0

0

100

0.5 A

–2.0

100

–40

80

–4.0

60

40

20 mV

–8.0

20

0

–10

0

00

40

80

120

60

20

–6.0

/DIV

I

Load

, LOAD CURRENT (A)

–20

–25

–25

–25

5.0

0

0

0

10

25

25

25

15

50

50

50

20

75

75

75

25

100

100

100

30

125

125

125

4035

Vin = 12 V
Normalized at 25

°

C

Adjustable
Version Only

CHANGE (mV)

CURRENT

LM2575

7

MOTOROLA ANALOG IC DEVICE DATA

Figure 14. Typical Test Circuit

D1
1N5819

L1

330

µ

H

Output

2

4

Feedback

C

out

330 µF
/16 V

C

in

100 µF/50 V

LM2575–5

1

53ON

/OFFGnd

V

in

Load

V

out

Regulated

Output

V

in

Unregulated

DC Input

8.0 V – 40 V

D1
1N5819

L1

330

µ

H

Output

2

4

Feedback

C

out

330 µF
/16 V

C

in

100 µF/50 V

LM2575

Adjustable

1

53ON

/OFFGnd

V

in

Load

V

out

Regulated

Output

Unregulated

DC Input

8.0 V – 40 V

5.0 Output Voltage Versions

Adjustable Output Voltage Versions

V

out

+

V

ref

ǒ

1

)

R2
R1

Ǔ

R2+R1

ǒ

V

out

V

ref

–1

Ǔ

Where V

ref

= 1.23 V, R1

between 1.0 k

Ω

and 5.0 k

Ω

R2

R1

+

–

+

–

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 14, 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 LM2575 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
LM2575 regulator.

LM2575

8

MOTOROLA ANALOG IC DEVICE DATA

PIN FUNCTION DESCRIPTION

Pin Symbol Description (Refer to Figure 1)

1 V

in

This pin is the positive input supply for the LM2575 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 (C

in

in Figure 1).

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

sat

of this output switch is typically 1.0 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 LM2575 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 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total

input supply current to approximately 80 µA. The input threshold voltage is typically 1.4 V . Applying a
voltage above this value (up to +V

in

) shuts the regulator off. If the voltage applied to this pin is lower than

1.4 V or if this pin is connected to ground, the regulator will be in the “on” condition.

DESIGN PROCEDURE

Buck Converter Basics

The LM2575 is a “Buck” or Step–Down Converter which is
the most elementary forward–mode converter. Its basic
schematic can be seen in

Figure 15.

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:

I

L(on)

+

ǒ

Vin–V

out

Ǔ

t

on

L

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 15. Basic Buck Converter

D1

V

in

V

out

R

Load

L

C

out

Power
Switch

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 catch dioded. 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:

I

L(off)

+

ǒ

V

out

–V

D

Ǔ

t

off

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

+

t

on

T

, where T is the period of switching.

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

d

+

V

out

V

in

Figure 16 shows the buck converter idealized waveforms
of the catch diode voltage and the inductor current.

Power
Switch

Figure 16. Buck Converter Idealized Waveforms

Power
Switch

Off

Power
Switch

Off

Power
Switch

On

Power

Switch

On

V

on(SW)

VD(FWD)

Time

Time

I

Load

(AV)

I

min

I

pk

Diode Diode

Power

Switch

Diode VoltageInductor Current

LM2575

9

MOTOROLA ANALOG IC DEVICE DATA

Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step–by–step

design procedure and example is provided.

Procedure Example

Given Parameters:

V

out

= Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V)

V

in(max)

= Maximum DC Input Voltage

I

Load(max)

= Maximum Load Current

Given Parameters:

V

out

= 5.0 V

V

in(max)

= 20 V

I

Load(max)

= 0.8 A

1. Controller IC Selection

According to the required input voltage, output voltage and
current, select the appropriate type of the controller IC output
voltage version.

1. Controller IC Selection

According to the required input voltage, output voltage, current
polarity and current value, use the LM2575–5 controller IC

2. Input Capacitor Selection (Cin)

To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +V

in

and ground pin Gnd. This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.

2. Input Capacitor Selection (Cin)

A 47 µF, 25 V aluminium electrolytic capacitor located near to
the input and ground pins provides sufficient bypassing.

3. Catch Diode Selection (D1)

A.Since the diode maximum peak current exceeds the

regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design the diode should have a
current rating equal to the maximum current limit of the
LM2575 to be able to withstand a continuous output short

B.The reverse voltage rating of the diode should be at least

1.25 times the maximum input voltage.

3. Catch Diode Selection (D1)

A.For this example the current rating of the diode is 1.0 A.

B.Use a 30 V 1N5818 Schottky diode, or any of the suggested

fast recovery diodes shown in the Table 4.

4. Inductor Selection (L1)

A.According to the required working conditions, select the

correct inductor value using the selection guide from
Figures 17 to 21

.

B.From the appropriate inductor selection guide, identify the

inductance region intersected by the Maximum Input
Voltage line and the Maximum Load Current line. Each
region is identified by an inductance value and an inductor
code.

C.Select an appropriate inductor from the several different

manufacturers part numbers listed in Table 1 or Table 2.
When using Table 2 for selecting the right inductor the
designer must realize that the inductor current rating must
be higher than the maximum peak current flowing through
the inductor. This maximum peak current can be calculated
as follows

:

where ton is the “on” time of the power switch and

For additional information about the inductor, see the
inductor section in the “External Components” section of
this data sheet.

I

p(max)

+

I

Load(max)

)

ǒ

Vin–V

out

Ǔ

t

on

2L

t

on

+

V

out

V

in

x

1

f

osc

4. Inductor Selection (L1)

A.Use the inductor selection guide shown in Figures 17 to 21.

B.From the selection guide, the inductance area intersected

by the 20 V line and 0.8 A line is L330.

C.Inductor value required is 330 µH. From the Table 1 or

Table 2

,

choose an inductor from any of the listed

manufacturers.

LM2575

10

MOTOROLA ANALOG IC DEVICE DATA

Procedure

(Fixed Output Voltage Version) (continued)In order to simplify the switching regulator design, a step–by–step

design procedure and example is provided.

Procedure Example

5. Output Capacitor Selection (C

out

)

A.Since the LM2575 is a forward–mode switching regulator

with voltage mode control, its open loop 2–pole–2–zero
frequency characteristic has the dominant pole–pair
determined by the output capacitor and inductor values. For
stable operation and an acceptable ripple voltage,
(approximately 1% of the output voltage) a value between
100 µF and 470 µF is recommended.

B.Due to the fact that the higher voltage electrolytic capacitors

generally have lower ESR (Equivalent Series Resistance)
numbers, the output capacitor’s voltage rating should be at
least 1.5 times greater than the output voltage. For a 5.0 V
regulator, a rating at least 8V is appropriate, and a 10 V or
16 V rating is recommended.

5. Output Capacitor Selection (C

out

)

A.C

out

= 100 µF to 470 µF standard aluminium electrolytic.

B.Capacitor voltage rating = 16 V.

Procedure (Adjustable Output Version: LM2575–Adj)

Procedure Example

Given Parameters:

V

out

= Regulated Output Voltage

V

in(max)

= Maximum DC Input Voltage

I

Load(max)

= Maximum Load Current

Given Parameters:

V

out

= 8.0 V

V

in(max)

= 12 V

I

Load(max)

= 1.0 A

1. Programming Output Voltage

To select the right programming resistor R1 and R2 value (see
Figure 14) use the following formula:

Resistor R1 can be between 1.0 k and 5.0 kΩ. (For best
temperature coefficient and stability with time, use 1% metal
film resistors).

V

out

+

V

ref

ǒ

1

)

R2
R1

Ǔ

R2+R1

ǒ

V

out

V

ref

–1

Ǔ

where V

ref

= 1.23 V

1. Programming Output Voltage (selecting R1 and R2)
Select R1 and R2:

R2 = 9.91 kΩ, choose a 9.88 k metal film resistor.

R2+R1

ǒ

V

out

V

ref

*

1Ǔ+

1.8 k

ǒ

8.0 V

1.23 V

*

1

Ǔ

V

out

+

1.23ǒ1

)

R2
R1

Ǔ

Select R1 = 1.8 kΩ

2. Input Capacitor Selection (Cin)

To prevent large voltage transients from appearing at the input
and for stable operation of the converter, an aluminium or
tantalum electrolytic bypass capacitor is needed between the
input pin +V

in

and ground pin Gnd This capacitor should be
located close to the IC using short leads. This capacitor should
have a low ESR (Equivalent Series Resistance) value.

For additional information see input capacitor section in the
“External Components” section of this data sheet.

2. Input Capacitor Selection (Cin)

A 100 µF aluminium electrolytic capacitor located near the
input and ground pin provides sufficient bypassing.

3. Catch Diode Selection (D1)

A.Since the diode maximum peak current exceeds the

regulator maximum load current the catch diode current
rating must be at least 1.2 times greater than the maximum
load current. For a robust design, the diode should have a
current rating equal to the maximum current limit of the
LM2575 to be able to withstand a continuous output short.

B.The reverse voltage rating of the diode should be at least

1.25 times the maximum input voltage.

3. Catch Diode Selection (D1)

A.For this example, a 3.0 A current rating is adequate.

B.Use a 20 V 1N5820 or MBR320 Schottky diode or any

suggested fast recovery diode in the Table 4.

LM2575

11

MOTOROLA ANALOG IC DEVICE DATA

Procedure (Adjustable Output Version: LM2575–Adj) (continued)

Procedure Example

4. Inductor Selection (L1)

A.Use the following formula to calculate the inductor Volt x

microsecond [V x µs] constant:

B.Match the calculated E x T value with the corresponding

number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 21. This E x T constant is a measure
of the energy handling capability of an inductor and is
dependent upon the type of core, the core area, the number
of turns, and the duty cycle.

C.Next step is to identify the inductance region intersected by

the E x T value and the maximum load current value on the
horizontal axis shown in Figure 21.

D.From the inductor code, identify the inductor value. Then

select an appropriate inductor from the Table 1 or Table 2.
The inductor chosen must be rated for a switching
frequency of 52 kHz and for a current rating of 1.15 x

I

Ioad

.
The inductor current rating can also be determined by
calculating the inductor peak current

:

where ton is the “on” time of the power switch and

For additional information about the inductor, see the
inductor section in the “External Components” section of
this data sheet.

ExT

+

ǒ

Vin–V

out

Ǔ

V

out

V

on

x

10

6

F[Hz]

[V xms]

I

p(max)

+

I

Load(max)

)

ǒ

Vin–V

out

Ǔ

t

on

2L

ton+

V

out

V

in

x

1

f

osc

4. Inductor Selection (L1)

A.Calculate E x T [V x µs] constant:

B.E x T = 51 [V x µs]

C.I

Load(max)

= 1.0 A

Inductance Region = L220

D.Proper inductor value = 220 µH

Choose the inductor from the Table 1 or Table 2.

ExT

+(12 – 8.0)x

8.0
12

x

1000

52

+

51 [V xms]

5. Output Capacitor Selection (C

out

)

A.Since the LM2575 is a forward–mode switching regulator

with voltage mode control, its open loop 2–pole–2–zero
frequency characteristic has the dominant pole–pair
determined by the output capacitor and inductor values.

For stable operation, the capacitor must satisfy the
following requirement:

B.Capacitor values between 10 µF and 2000 µF will satisfy

the loop requirements for stable operation. To achieve an
acceptable output ripple voltage and transient response, the
output capacitor may need to be several times larger than
the above formula yields.

C.Due to the fact that the higher voltage electrolytic capacitors

generally have lower ESR (Equivalent Series Resistance)
numbers, the output capacitor’s voltage rating should be at
least 1.5 times greater than the output voltage. For a 5.0 V
regulator, a rating of at least 8V is appropriate, and a 10 V
or 16 V rating is recommended.

C

out

w

7.785

V

in(max)

V

out

xL[µH]

[µF]

5. Output Capacitor Selection (C

out

)

A.

To achieve an acceptable ripple voltage, select
C

out

= 100 µF electrolytic capacitor.

C

out

w

7.785

12

8.220

+

53 µF

LM2575

12

MOTOROLA ANALOG IC DEVICE DATA

INDUCTOR VALUE SELECTION GUIDE

V

in

, MAXIMUM INPUT VOLTAGE (V)

V

in

, MAXIMUM INPUT VOLTAGE (V) V

in

, MAXIMUM INPUT VOLTAGE (V)

IL, MAXIMUM LOAD CURRENT (A) IL, MAXIMUM LOAD CURRENT (A)

IL, MAXIMUM LOAD CURRENT (A)

0.2

60

0.2

60

0.2

200

0.2

60

0.2

60

ET, VOLTAGE TIME (V s)

µ

IL, MAXIMUM LOAD CURRENT (A)

V

in

, MAXIMUM INPUT VOLTAGE (V)

Figure 17. LM2575–3.3

IL, MAXIMUM LOAD CURRENT (A)

Figure 18. LM2575–5.0

Figure 19. LM2575–12 Figure 20. LM2575–15

Figure 21. LM2575–Adj

NOTE: This Inductor Value Selection Guide is applicable for continuous mode only.

H1500H1000

L680

L470

L330

L150

H1000

L100

L680

L470

L330

L220

L150

H1500

H1000

H1500

H1000

H680

H470

H680

H680

H2200

H2200

H2200

H1500

H1000

H470

H470

L330

L220

L150

L680

L680

L680

L470

L470

L470

L100

L220

L220

L330

L330

40

40

150

20

35

25

125

40

15

30

20

100

30

10

25

15

80

25

8.0

22

12

70

20

7.0

20

10

60

18

6.0

19

9.0

50

17

18

8.0

40

16

17

7.0

20

14

5.0

0.3

0.3

0.3

0.3

0.3

0.4

0.4

0.4

0.4

0.4

0.5

0.5

0.5

0.5

0.5

0.6

0.6

0.6

0.6

0.6

0.7

0.7

0.7

0.7 0.8

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9 1.0

1.0

1.0

1.0

1.0

15

30

L220

LM2575

13

MOTOROLA ANALOG IC DEVICE DATA

Table 1. Inductor Selection Guide

Inductor

Code

Inductor

Value

Pulse Eng Renco AIE Tech 39

L100 100 µH PE–92108 RL2444 415–0930 77 308 BV
L150 150 µH PE–53113 RL1954 415–0953 77 358 BV
L220 220 µH PE–52626 RL1953 415–0922 77 408 BV
L330 330 µH PE–52627 RL1952 415–0926 77 458 BV
L470 470 µH PE–53114 RL1951 415–0927 –

L680 680 µH PE–52629 RL1950 415–0928 77 508 BV
H150 150 µH PE–53115 RL2445 415–0936 77 368 BV
H220 220 µH PE–53116 RL2446 430–0636 77 410 BV
H330 330 µH PE–53117 RL2447 430–0635 77 460 BV
H470 470 µH PE–53118 RL1961 430–0634 –
H680 680 µH PE–53119 RL1960 415–0935 77 510 BV

H1000 1000 µH PE–53120 RL1959 415–0934 77 558 BV
H1500 1500 µH PE–53121 RL1958 415–0933 –
H2200 2200 µH PE–53122 RL2448 415–0945 77 610 BV

Table 2. Inductor Selection Guide

Inductance Current Schott Renco Pulse Engineering Coilcraft

(µH) (A) THT SMT THT SMT THT SMT SMT

0.32 67143940 67144310 RL–1284–68–43 RL1500–68 PE–53804 PE–53804–S DO1608–68

0.58 67143990 67144360 RL–5470–6 RL1500–68 PE–53812 PE–53812–S DO3308–683

68

0.99 67144070 67144450 RL–5471–5 RL1500–68 PE–53821 PE–53821–S DO3316–683

1.78 67144140 67144520 RL–5471–5 – PE–53830 PE–53830–S DO5022P–683

0.48 67143980 67144350 RL–5470–5 RL1500–100 PE–53811 PE–53811–S DO3308–104

100

0.82 67144060 67144440 RL–5471–4 RL1500–100 PE–53820 PE–53820–S DO3316–104

1.47 67144130 67144510 RL–5471–4 – PE–53829 PE–53829–S DO5022P–104

0.39 – 67144340 RL–5470–4 RL1500–150 PE–53810 PE–53810–S DO3308–154

150

0.66 67144050 67144430 RL–5471–3 RL1500–150 PE–53819 PE–53819–S DO3316–154

1.20 67144120 67144500 RL–5471–3 – PE–53828 PE–53828–S DO5022P–154

0.32 67143960 67144330 RL–5470–3 RL1500–220 PE–53809 PE–53809–S DO3308–224

220

0.55 67144040 67144420 RL–5471–2 RL1500–220 PE–53818 PE–53818–S DO3316–224

1.00 67144110 67144490 RL–5471–2 – PE–53827 PE–53827–S DO5022P–224

0.42 67144030 67144410 RL–5471–1 RL1500–330 PE–53817 PE–53817–S DO3316–334

330

0.80 67144100 67144480 RL–5471–1 – PE–53826 PE–53826–S DO5022P–334

NOTE: Table 1 and Table 2 of this Indicator Selection Guide shows some examples of different manufacturer products suitable for design with the LM2575.

LM2575

14

MOTOROLA ANALOG IC DEVICE DATA

Table 3. Example of Several Inductor Manufacturers Phone/Fax Numbers

Pulse Engineering Inc.

Phone
Fax

+ 1–619–674–8100
+ 1–619–674–8262

Pulse Engineering Inc. Europe

Phone
Fax

+ 353 93 24 107
+ 353 93 24 459

Renco Electronics Inc.

Phone
Fax

+ 1–516–645–5828
+ 1–516–586–5562

AIE Magnetics

Phone
Fax

+ 1–813–347–2181

Coilcraft Inc.

Phone
Fax

+ 1–708–322–2645
+ 1–708–639–1469

Coilcraft Inc., Europe

Phone
Fax

+ 44 1236 730 595
+ 44 1236 730 627

Tech 39

Phone
Fax

+ 33 8425 2626
+ 33 8425 2610

Schott Corp.

Phone
Fax

+ 1–612–475–1173
+ 1–612–475–1786

Table 4. Diode Selection Guide gives an overview about both surface–mount and through–hole diodes for an

effective design. Device listed in bold are available from Motorola.

Schottky Ultra–Fast Recovery

1.0 A 3.0 A 1.0 A 3.0 A

V

R

SMT THT SMT THT SMT THT SMT THT

20 V SK12 1N5817

SR102

SK32

MBRD320

1N5820

MBR320

SR302

30 V MBRS130LT3

SK13

1N5818

SR103

11DQ03

SK33

MBRD330

1N5821

MBR330

SR303

31DQ03

MURS120T3

MUR120

11DF1

HER102

MURS320T3

40 V MBRS140T3

SK14

10BQ040

10MQ040

1N5819

SR104

11DQ04

MBRS340T3

MBRD340

30WQ04

SK34

1N5822

MBR340

SR304

31DQ04

10BF10 MURD320 MUR320

30WF10

MUR420

50 V MBRS150

10BQ050

MBR150

SR105

11DQ05

MBRD350

SK35

30WQ05

MBR350

SR305

11DQ05

31DF1

HER302

LM2575

15

MOTOROLA ANALOG IC DEVICE DATA

EXTERNAL COMPONENTS

Input Capacitor (Cin)

The Input Capacitor Should Have a Low ESR

For stable operation of the switch mode converter a low
ESR (Equivalent Series Resistance) aluminium or solid
tantalum bypass capacitor is needed between the input pin
and the ground pin to prevent large voltage transients from
appearing at the input. It must be located near the regulator
and use short leads. With most electrolytic capacitors, the
capacitance value decreases and the ESR increases with
lower temperatures. For reliable operation in temperatures
below –25°C larger values of the input capacitor may be
needed. Also paralleling a ceramic or solid tantalum
capacitor will increase the regulator stability at cold
temperatures.

RMS Current Rating of C

in

The important parameter of the input capacitor is the RMS
current rating. Capacitors that are physically large and have
large surface area will typically have higher RMS current
ratings. For a given capacitor value, a higher voltage
electrolytic capacitor will be physically larger than a lower
voltage capacitor, and thus be able to dissipate more heat to
the surrounding air, and therefore will have a higher RMS
current rating. The consequence of operating an electrolytic
capacitor above the RMS current rating is a shortened
operating life. In order to assure maximum capacitor
operating lifetime, the capacitor’s RMS ripple current rating
should be:

I

rms

> 1.2 x d x I

Load

where d is the duty cycle, for a buck regulator

d

+

t

on

T

+

V

out

V

in

and d

+

t

on

T

+

|V

out

|

|V

out

|)V

in

for a buck*boost regulator.

Output Capacitor (C

out

)

For low output ripple voltage and good stability, low ESR
output capacitors are recommended. An output capacitor has
two main functions: it filters the output and provides regulator
loop stability. The ESR of the output capacitor and the
peak–to–peak value of the inductor ripple current are the
main factors contributing to the output ripple voltage
value.Standard aluminium electrolytics could be adequate for
some applications but for quality design low ESR types are
recommended.

An aluminium electrolytic capacitor’s ESR value is related
to many factors such as the capacitance value, the voltage
rating, the physical size and the type of construction. In most
cases, the higher voltage electrolytic capacitors have lower
ESR value. Often capacitors with much higher voltage
ratings may be needed to provide low ESR values that are
required for low output ripple voltage.

The Output Capacitor Requires an ESR Value
That Has an Upper and Lower Limit

As mentioned above, a low ESR value is needed for low
output ripple voltage, typically 1% to 2% of the output voltage.
But if the selected capacitor’s ESR is extremely low (below

0.05 Ω), there is a possibility of an unstable feedback loop,
resulting in oscillation at the output. This situation can occur
when a tantalum capacitor, that can have a very low ESR, is
used as the only output capacitor.

At Low Temperatures, Put in Parallel Aluminium
Electrolytic Capacitors with Tantalum Capacitors

Electrolytic capacitors are not recommended for
temperatures below –25°C. The ESR rises dramatically at
cold temperatures and typically rises 3 times at –25°C and as
much as 10 times at –40°C. Solid tantalum capacitors have
much better ESR spec at cold temperatures and are
recommended for temperatures below –25°C. They can be
also used in parallel with aluminium electrolytics. The value
of the tantalum capacitor should be about 10% or 20% of the
total capacitance. The output capacitor should have at least
50% higher RMS ripple current rating at 52 kHz than the
peak–to–peak inductor ripple current.

Catch Diode

Locate the Catch Diode Close to the LM2575

The LM2575 is a step–down buck converter; it requires a
fast diode to provide a return path for the inductor current
when the switch turns off. This diode must be located close to
the LM2575 using short leads and short printed circuit traces
to avoid EMI problems.

Use a Schottky or a Soft Switching
Ultra–Fast Recovery Diode

Since the rectifier diodes are very significant source of
losses within switching power supplies, choosing the rectifier
that best fits into the converter design is an important
process. Schottky diodes provide the best performance
because of their fast switching speed and low forward
voltage drop.

They provide the best efficiency especially in low output
voltage applications (5.0 V and lower). Another choice could
be Fast–Recovery, or Ultra–Fast Recovery diodes. It has to
be noted, that some types of these diodes with an abrupt
turnoff characteristic may cause instability or EMI troubles.

A fast–recovery diode with soft recovery characteristics
can better fulfill a quality, low noise design requirements.
Table 4 provides a list of suitable diodes for the LM2575
regulator. Standard 50/60 Hz rectifier diodes such as the
1N4001 series or 1N5400 series are NOT suitable.

Inductor

The magnetic components are the cornerstone of all
switching power supply designs. The style of the core and
the winding technique used in the magnetic component’s
design has a great influence on the reliability of the overall
power supply.

Using an improper or poorly designed inductor can cause
high voltage spikes generated by the rate of transitions in
current within the switching power supply, and the possibility
of core saturation can arise during an abnormal operational
mode. Voltage spikes can cause the semiconductors to enter
avalanche breakdown and the part can instantly fail if enough
energy is applied. It can also cause significant RFI (Radio
Frequency Interference) and EMI (Electro–Magnetic
Interference) problems.

Continuous and Discontinuous Mode of Operation

The LM2575 step–down converter can operate in both the
continuous and the discontinuous modes of operation. The
regulator works in the continuous mode when loads are
relatively heavy, the current flows through the inductor
continuously and never falls to zero. Under light load

LM2575

16

MOTOROLA ANALOG IC DEVICE DATA

conditions, the circuit will be forced to the discontinuous
mode when inductor current falls to zero for certain period of
time (see Figure 22 and Figure 23). Each mode has
distinctively different operating characteristics, which can
affect the regulator performance and requirements. In many
cases the preferred mode of operation is the continuous
mode. It offers greater output power, lower peak currents in
the switch, inductor and diode, and can have a lower output
ripple voltage. On the other hand it does require larger
inductor values to keep the inductor current flowing
continuously, especially at low output load currents and/or
high input voltages.

To simplify the inductor selection process, an inductor
selection guide for the LM2575 regulator was added to this
data sheet (Figures 17

through 21). This guide assumes that
the regulator is operating in the continuous mode, and
selects an inductor that will allow a peak–to–peak inductor
ripple current to be a certain percentage of the maximum
design load current. This percentage is allowed to change as
different design load currents are selected. For light loads
(less than approximately 200 mA) it may be desirable to
operate the regulator in the discontinuous mode, because
the inductor value and size can be kept relatively low.
Consequently, the percentage of inductor peak–to–peak
current increases. This discontinuous mode of operation is
perfectly acceptable for this type of switching converter. Any
buck regulator will be forced to enter discontinuous mode if
the load current is light enough.

Figure 22. Continuous Mode Switching

Current Waveforms

POWER SWITCH

1.0

0

0

CURRENT (A)

HORTIZONTAL TIME BASE: 5.0 µs/DIV

1.0

INDUCTOR

CURRENT (A)

Selecting the Right Inductor Style

Some important considerations when selecting a core
type are core material, cost, the output power of the power
supply, the physical volume the inductor must fit within, and
the amount of EMI (Electro–Magnetic Interference) shielding
that the core must provide. The inductor selection guide
covers different styles of inductors, such as pot core, E–core,

toroid and bobbin core, as well as different core materials
such as ferrites and powdered iron from different
manufacturers.

For high quality design regulators the toroid core seems to
be the best choice. Since the magnetic flux is completely
contained within the core, it generates less EMI, reducing
noise problems in sensitive circuits. The least expensive is
the bobbin core type, which consists of wire wound on a
ferrite rod core. This type of inductor generates more EMI
due to the fact that its core is open, and the magnetic flux is
not completely contained within the core.

When multiple switching regulators are located on the
same printed circuit board, open core magnetics can cause
interference between two or more of the regulator circuits,
especially at high currents due to mutual coupling. A toroid,
pot core or E–core (closed magnetic structure) should be
used in such applications.

Do Not Operate an Inductor Beyond its
Maximum Rated Current

Exceeding an inductor’s maximum current rating may
cause the inductor to overheat because of the copper wire
losses, or the core may saturate. Core saturation occurs
when the flux density is too high and consequently the cross
sectional area of the core can no longer support additional
lines of magnetic flux.

This causes the permeability of the core to drop, the
inductance value decreases rapidly and the inductor begins
to look mainly resistive. It has only the dc resistance of the
winding. This can cause the switch current to rise very rapidly
and force the LM2575 internal switch into cycle–by–cycle
current limit, thus reducing the dc output load current. This
can also result in overheating of the inductor and/or the
LM2575. Different inductor types have different saturation
characteristics, and this should be kept in mind when
selecting an inductor.

Figure 23. Discontinuous Mode Switching

Current Waveforms

0.1

0.1

0

0

HORTIZONTAL TIME BASE: 5.0

µ

s/DIV

POWER SWITCH

CURRENT (A)

INDUCTOR

CURRENT (A)

LM2575

17

MOTOROLA ANALOG IC DEVICE DATA

GENERAL RECOMMENDATIONS

Output Voltage Ripple and Transients

Source of the Output Ripple

Since the LM2575 is a switch mode power supply
regulator, its output voltage, if left unfiltered, will contain a
sawtooth ripple voltage at the switching frequency. The
output ripple voltage value ranges from 0.5% to 3% of the
output voltage. It is caused mainly by the inductor sawtooth
ripple current multiplied by the ESR of the output capacitor.

Short Voltage Spikes and How to Reduce Them

The regulator output voltage may also contain short
voltage spikes at the peaks of the sawtooth waveform (see
Figure 24). These voltage spikes are present because of the
fast switching action of the output switch, and the parasitic
inductance of the output filter capacitor. There are some
other important factors such as wiring inductance, stray
capacitance, as well as the scope probe used to evaluate
these transients, all these contribute to the amplitude of these
spikes. To minimise these voltage spikes, low inductance
capacitors should be used, and their lead lengths must be
kept short. The importance of quality printed circuit board
layout design should also be highlighted.

Figure 24. Output Ripple Voltage Waveforms

HORTIZONTAL TIME BASE: 10 µs/DIV

UNFILITERED
OUTPUT
VOLTAGE

VERTICAL
RESOLUTION:
20 mV/DIV

FILITERED
OUTPUT
VOLTAGE

Voltage spikes caused by switching action of the output
switch and the parasitic inductance of the output capacitor

Minimizing the Output Ripple

In order to minimise the output ripple voltage it is possible
to enlarge the inductance value of the inductor L1 and/or to
use a larger value output capacitor. There is also another way
to smooth the output by means of an additional LC filter
(20 µH, 100 µF), that can be added to the output (see
Figure 33) to further reduce the amount of output ripple and
transients. With such a filter it is possible to reduce the
output ripple voltage transients 10 times or more. Figure 24
shows the difference between filtered and unfiltered output
waveforms of the regulator shown in Figure 33.

The upper waveform is from the normal unfiltered output of
the converter, while the lower waveform shows the output
ripple voltage filtered by an additional LC filter.

Heatsinking and Thermal Considerations

The Through–Hole Package TO–220

The LM2575 is available in two packages, a 5–pin
TO–220(T, TV) and a 5–pin surface mount D

2

PAK(D2T).
There are many applications that require no heatsink to keep
the LM2575 junction temperature within the allowed
operating range. The TO–220 package can be used without

a heatsink for ambient temperatures up to approximately
50°C (depending on the output voltage and load current).
Higher ambient temperatures require some heatsinking,
either to the printed circuit (PC) board or an external heatsink.

The Surface Mount Package D2PAK and its Heatsinking

The other type of package, the surface mount D2PAK, is
designed to be soldered to the copper on the PC board. The
copper and the board are the heatsink for this package and
the other heat producing components, such as the catch
diode and inductor. The PC board copper area that the
package is soldered to should be at least 0.4 in

2

(or

100 mm

2

) and ideally should have 2 or more square inches

(1300 mm

2

) of 0.0028 inch copper. Additional increasing of

copper area beyond approximately 3.0 in

2

(2000 mm2) will
not improve heat dissipation significantly. If further thermal
improvements are needed, double sided or multilayer PC
boards with large copper areas should be considered.

Thermal Analysis and Design

The following procedure must be performed to determine

whether or not a heatsink will be required. First determine:

1. P

D(max)

maximum regulator power dissipation in the

application.

2. T

A(max

) maximum ambient temperature in the

application.

3. T

J(max)

maximum allowed junction temperature
(125°C for the LM2575). For a conservative
design, the maximum junction temperature
should not exceed 110 °C to assure safe
operation. For every additional 10°C
temperature rise that the junction must
withstand, the estimated operating lifetime of
the component is halved.

4. R

θ

JC

package thermal resistance junction–case.

5. R

θ

JA

package thermal resistance junction–ambient.

(Refer to Absolute Maximum Ratings in this data sheet or
R

θ

JC

and R

θ

JA

values).

The following formula is to calculate the total power

dissipated by the LM2575:

P

D

= (Vin x IQ) + d x I

Load

x V

sat

where d is the duty cycle and for buck converter

d

+

t

on

T

+

V

O

V

in

,

I

Q

(quiescent current) and V

sat

can be found in the

LM2575 data sheet,

V

in

is minimum input voltage applied,

V

O

is the regulator output voltage,

I

Load

is the load current.

The dynamic switching losses during turn–on and turn–off

can be neglected if proper type catch diode is used.

Packages Not on a Heatsink (Free–Standing)

For a free–standing application when no heatsink is used,
the junction temperature can be determined by the following
expression:

T

J

= (R

θ

JA

) (PD) + T

A

where (R

θ

JA

)(PD) represents the junction temperature rise

caused by the dissipated power and T

A

is the maximum

ambient temperature.

LM2575

18

MOTOROLA ANALOG IC DEVICE DATA

Packages on a Heatsink

If the actual operating junction temperature is greater than
the selected safe operating junction temperature determined
in step 3, than a heatsink is required. The junction
temperature will be calculated as follows:

T

J

= PD (R

θ

JA

+ R

θ

CS

+ R

θ

SA

) + T

A

where R

θ

JC

is the thermal resistance junction–case,

R

θ

CS

is the thermal resistance case–heatsink,

R

θ

SA

is the thermal resistance heatsink–ambient.

If the actual operating temperature is greater than the
selected safe operating junction temperature, then a larger
heatsink is required.

Some Aspects That can Influence Thermal Design

It should be noted that the package thermal resistance and
the junction temperature rise numbers are all approximate,
and there are many factors that will affect these numbers,
such as PC board size, shape, thickness, physical position,
location, board temperature, as well as whether the
surrounding air is moving or still.

Other factors are trace width, total printed circuit copper
area, copper thickness, single– or double–sided, multilayer
board, the amount of solder on the board or even colour of
the traces.

The size, quantity and spacing of other components on
the board can also influence its effectiveness to dissipate
the heat.

Figure 25. Inverting Buck–Boost Regulator Using the

LM2575–12 Develops –12 V @ 0.35 A

D1
1N5819

L1

100

µ

H

Output
2

4

Feedback

Unregulated
DC Input
12 V to 25 V

C

in

100 µF

/50 V

1

53ON

/OFFGnd

+V

in

Regulated

Output

–12 V @ 0.35 A

C

out

1800 µF
/16 V

LM2575–12

ADDITIONAL APPLICATIONS

Inverting Regulator

An inverting buck–boost regulator using the LM2575–12 is
shown in Figure 25. This circuit converts a positive input
voltage to a negative output voltage with a common ground
by bootstrapping the regulators ground to the negative output
voltage. By grounding the feedback pin, the regulator senses
the inverted output voltage and regulates it.

In this example the LM2575–12 is used to generate a
–12 V output. The maximum input voltage in this case

cannot exceed +28 V because the maximum voltage
appearing across the regulator is the absolute sum of the
input and output voltages and this must be limited to a
maximum of 40 V.

This circuit configuration is able to deliver approximately

0.35 A to the output when the input voltage is 12 V or higher.
At lighter loads the minimum input voltage required drops to
approximately 4.7 V, because the buck–boost regulator
topology can produce an output voltage that, in its absolute
value, is either greater or less than the input voltage.

Since the switch currents in this buck–boost configuration
are higher than in the standard buck converter topology, the
available output current is lower.

This type of buck–boost inverting regulator can also
require a larger amount of startup input current, even for light
loads. This may overload an input power source with a
current limit less than 1.5 A.

Such an amount of input startup current is needed for at
least 2.0 ms or more. The actual time depends on the output
voltage and size of the output capacitor.

Because of the relatively high startup currents required by
this inverting regulator topology, the use of a delayed startup
or an undervoltage lockout circuit is recommended.

Using a delayed startup arrangement, the input capacitor
can charge up to a higher voltage before the switch–mode
regulator begins to operate.

The high input current needed for startup is now partially
supplied by the input capacitor C

in

.

Design Recommendations:

The inverting regulator operates in a different manner than
the buck converter and so a different design procedure has to
be used to select the inductor L1 or the output capacitor C

out

.

The output capacitor values must be larger than is
normally required for buck converter designs. Low input
voltages or high output currents require a large value output
capacitor (in the range of thousands of µF).

The recommended range of inductor values for the
inverting converter design is between 68 µH and 220 µH. To
select an inductor with an appropriate current rating, the
inductor peak current has to be calculated.

The following formula is used to obtain the peak inductor
current:

where ton+

|VO|

Vin)

|VO|

x

1

f

osc

, and f

osc

+

52 kHz.

I

peak

[

I

Load(Vin

)

|VO|)

V

in

)

Vinxt

on

2L

1

Under normal continuous inductor current operating
conditions, the worst case occurs when V

in

is minimal.

Note that the voltage appearing across the regulator is the
absolute sum of the input and output voltage, and must not
exceed 40 V.

LM2575

19

MOTOROLA ANALOG IC DEVICE DATA

Figure 26. Inverting Buck–Boost

Regulator with Delayed Startup

D1
1N5819

L1

100

µ

H

Output
2

4

Feedback

Unregulated
DC Input
12 V to 25 V

C

in

100 µF

/50 V

1

35ON

/OFF Gnd

+V

in

Regulated

Output

–12 V @ 0.35 A

C

out

1800 µF
/16 V

LM2575–12

C1

0.1

µ

F

R1

47 k

R2
47 k

It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
features could be very useful. A delayed startup circuit
applied to a buck–boost converter is shown in Figure 26.
Figure 32 in the “Undervoltage Lockout” section describes an
undervoltage lockout feature for the same converter
topology.

Figure 27. Inverting Buck–Boost Regulator Shut Down

Circuit Using an Optocoupler

LM2575–XX

1

35 GndON/OFF

+V

in

R2
47 k

C

in

100 µF

NOTE: This picture does not show the complete circuit.

R1

47 k

R3

470

Shutdown
Input

MOC8101

–V

out

Off

On

5.0 V
0

+V

in

With the inverting configuration, the use of the ON/OFF pin
requires some level shifting techniques. This is caused by the
fact, that the ground pin of the converter IC is no longer at
ground. Now, the ON

/OFF pin threshold voltage (1.4 V
approximately) has to be related to the negative output
voltage level. There are many different possible shut down
methods, two of them are shown in Figures 27

and 28.

Figure 28. Inverting Buck–Boost Regulator Shut Down

Circuit Using a PNP Transistor

NOTE: This picture does not show the complete circuit.

R2

5.6 k

Q1
2N3906

LM2575–XX

1

35 GndON/OFF

R1
12 k

–V

out

+V

in

Shutdown
Input

Off

On

+V

0

+V

in

C

in

100 µF

Negative Boost Regulator

This example is a variation of the buck–boost topology and
is called a negative boost regulator. This regulator
experiences relatively high switch current, especially at low
input voltages. The internal switch current limiting results in
lower output load current capability.

The circuit in Figure 29 shows the negative boost
configuration. The input voltage in this application ranges
from –5.0 V to –12 V and provides a regulated –12 V output.
If the input voltage is greater than –12 V, the output will rise
above –12 V accordingly, but will not damage the regulator.

Figure 29. Negative Boost Regulator

1N5817

150

µ

H

Output
2

4
Feedback

Regulated

Output

V

out

= –12 V

Load Current from
200 mA for V

in

= –5.2 V

to 500 mA for V

in

= –7.0 V

Unregulated
DC Input
–V

in

= –5.0 V to –12 V

L1

D1

C

out

1000 µF
/16 V

C

in

100 µF

/50 V

LM2575–12

1

53

ON

/OFFGnd

+V

in

LM2575

20

MOTOROLA ANALOG IC DEVICE DATA

Design Recommendations:

The same design rules as for the previous inverting
buck–boost converter can be applied. The output capacitor
C

out

must be chosen larger than would be required for a
standard buck converter. Low input voltages or high output
currents require a large value output capacitor (in the range
of thousands of µF). The recommended range of inductor
values for the negative boost regulator is the same as for
inverting converter design.

Another important point is that these negative boost
converters cannot provide current limiting load protection in
the event of a short in the output so some other means, such
as a fuse, may be necessary to provide the load protection.

Delayed Startup

There are some applications, like the inverting regulator
already mentioned above, which require a higher amount of
startup current. In such cases, if the input power source is
limited, this delayed startup feature becomes very useful.

T o provide a time delay between the time the input voltage
is applied and the time when the output voltage comes up,
the circuit in Figure 30 can be used. As the input voltage is
applied, the capacitor C1 charges up, and the voltage across
the resistor R2 falls down. When the voltage on the ON

/OFF
pin falls below the threshold value 1.4 V, the regulator starts
up. Resistor R1 is included to limit the maximum voltage
applied to the ON

/OFF pin, reduces the power supply noise
sensitivity, and also limits the capacitor C1 discharge current,
but its use is not mandatory.

When a high 50 Hz or 60 Hz (100 Hz or 120 Hz
respectively) ripple voltage exists, a long delay time can
cause some problems by coupling the ripple into the ON

/OFF
pin, the regulator could be switched periodically on and off
with the line (or double) frequency.

Figure 30. Delayed Startup Circuitry

R1

47 k

LM2575–XX

1

35 GndON/OFF

R2
47 k

+V

in

+V

in

C1

0.1

µ

F

C

in

100 µF

NOTE: This picture does not show the complete circuit.

Undervoltage Lockout

Some applications require the regulator to remain off until
the input voltage reaches a certain threshold level. Figure 31
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buck–boost converter is

shown in Figure 32. Resistor R3 pulls the ON

/OFF pin high
and keeps the regulator off until the input voltage reaches a
predetermined threshold level, which is determined by the
following expression:

Vth[

VZ1)

ǒ

1

)

R2
R1

Ǔ

V

BE

(Q1)

Figure 31. Undervoltage Lockout Circuit for

Buck Converter

R2

10 k

Z1

1N5242B

R1

10 k

Q1
2N3904

R3

47 k

Vth ≈ 13 V

C

in

100 µF

LM2575–5.0

1

35 GndON/OFF

+V

in

+V

in

NOTE: This picture does not show the complete circuit.

Figure 32. Undervoltage Lockout Circuit for

Buck–Boost Converter

R2

15 k

Z1

1N5242B

R1

15 k

Q1
2N3904

R3

68 k

Vth ≈ 13 V

C

in

100 µF

LM2575–5.0

1

35 GndON/OFF

+V

in

+V

in

V

out

= –5.0 V

NOTE: This picture does not show the complete circuit.

Adjustable Output, Low–Ripple Power Supply

A 1.0 A output current capability power supply that

features an adjustable output voltage is shown in Figure 33.

This regulator delivers 1.0 A into 1.2 V to 35 V output. The
input voltage ranges from roughly 8.0 V to 40 V. In order to
achieve a 10 or more times reduction of output ripple, an
additional L–C filter is included in this circuit.

LM2575

21

MOTOROLA ANALOG IC DEVICE DATA

Figure 33. Adjustable Power Supply with Low Ripple Voltage

D1
1N5819

L1

150

µ

H

Output

2

4

Feedback

R2
50 k

R1

1.1 k

L2

20

µ

H

Regulated
Output Voltage

1.2 V to 35 V @1.0 A

Optional Output

Ripple Filter

Unregulated
DC Input
+

C

out

2200 µF

C1

100

µ

F

C

in

100 µF

/50 V

LM2575–Adj

1

53ON

/OFFGnd

+V

in

R , THERMAL RESIST ANCE

JA

θ

JUNCTION-TO-AIR ( C/W)

°

30

40

50

60

70

80

1.0

1.5

2.0

2.5

3.0

3.5

010203025155.0
L, LENGTH OF COPPER (mm)

Minimum
Size Pad

2.0 oz. Copper
L

L

Free Air
Mounted
Vertically

P

D

, MAXIMUM POWER DISSIPATION (W)

Figure 34. D2PAK Thermal Resistance and Maximum

Power Dissipation versus P.C.B. Copper Length

P

D(max)

for TA = 50°C

R

θ

JA

LM2575

22

MOTOROLA ANALOG IC DEVICE DATA

THE LM2575–5.0 STEP–DOWN VOL TAGE REGULATOR WITH 5.0 V @ 1.0 A OUTPUT POWER CAPABILITY.

TYPICAL APPLICATION WITH THROUGH–HOLE PC BOARD LAYOUT

DC–DC Converter

Figure 35. Schematic Diagram of the LM2575–5.0 Step–Down Converter

Figure 36. Printed Circuit Board

Component Side

Figure 37. Printed Circuit Board

Copper Side

D1
1N5819

L1

330

µ

H

Output
2

4

Feedback

Unregulated

DC Input

+V

in

= +7.0 V to +40 V

C

out

330 µF
/16 V

C1

100

µ

F

/50 V

LM2575–5.0

1

53ON

/OFFGnd

+V

in

J1

Regulated Output
+V

out1

= 5.0 V @ 1.0 A

Gnd

in

Gnd

out

C1 – 100 µF, 50 V, Aluminium Electrolytic
C2 – 330 µF, 16 V, Aluminium Electrolytic
D1 – 1.0 A, 40 V, Schottky Rectifier, 1N5819
L1 – 330 µH, Tech 39: 77 458 BV, T oroid Core, Through–Hole, Pin 3 = Start, Pin 7 = Finish

NOTE: Not to scale. NOTE: Not to scale.

+V

out1

+V

in

Gnd

in

Gnd

out

C1

L1

C2

D1

J1

U1 LM2575

LM2575

23

MOTOROLA ANALOG IC DEVICE DATA

THE LM2575–ADJ STEP–DOWN VOL TAGE REGULATOR WITH 8.0 V @ 1.0 A OUTPUT POWER

CAPABILITY. TYPICAL APPLICATION WITH THROUGH–HOLE PC BOARD LAYOUT

C1 – 100 µF, 50 V, Aluminium Electrolytic
C2 – 330 µF, 16 V, Aluminium Electrolytic
C3 – 100 µF, 16 V, Aluminium Electrolytic
D1 – 1.0 A, 40 V, Schottky Rectifier, 1N5819
L1 – 330 µH, Tech 39: 77 458 BV, T oroid Core, Through–Hole, Pin 3 = Start, Pin 7 = Finish
L2 – 25 µH, TDK: SFT52501, Toroid Core, Through–Hole
R1 – 1.8 k
R2 – 10 k

Figure 38. Schematic Diagram of the 8.0 V @ 1.0 V Step–Down Converter Using the LM2575–Adj

(An additional LC filter is included to achieve low output ripple voltage)

Figure 39. PC Board Component Side Figure 40. PC Board Copper Side

V

ref

= 1.23 V

R1 is between 1.0 k and 5.0 k

D1
1N5819

L1

330

µ

H

Output

2

R2
10 k

R1

1.8 k

L2

25

µ

H

Regulated
Output Filtered

V

out2

= 8.0 V @1.0 A

Unregulated
DC Input

C2
330

µ

F

/16 V

C3

100

µ

F

/16 V

C1

100

µ

F

/50 V

LM2575–Adj

1

53ON

/OFFGnd

+V

in

+Vin = +10 V to + 40 V

4 Feedback

Regulated
Output Unfiltered

V

out1

= 8.0 V @1.0 A

V

out

+

V

ref

)ǒ1

)

R2
R1

Ǔ

+V

out1

+V

in

Gnd

in

C1

L1

C2

D1

J1

U1 LM2575

L2

C3

+V

out2

R2 R1

Gnd

out

MOTOROLA

NOTE: Not to scale. NOTE: Not to scale.

References

• National Semiconductor LM2575 Data Sheet and Application Note

• National Semiconductor LM2595 Data Sheet and Application Note

• Marty Brown “Pratical Switching Power Supply Design”, Academic Press, Inc., San Diego 1990

• Ray Ridley “High Frequency Magnetics Design”, Ridley Engineering, Inc. 1995

LM2575

24

MOTOROLA ANALOG IC DEVICE DATA

T SUFFIX

PLASTIC PACKAGE

CASE 314D–03

ISSUE D

TV SUFFIX

PLASTIC PACKAGE

CASE 314B–05

ISSUE J

OUTLINE DIMENSIONS

–Q–

12345

U

K

D

G

S

A

B

5 PL

J
H

L

E

C

M

Q

M

0.356 (0.014) T

SEATING
PLANE

–T–

DIM MIN MAX MIN MAX

MILLIMETERSINCHES

A 0.572 0.613 14.529 15.570
B 0.390 0.415 9.906 10.541
C 0.170 0.180 4.318 4.572
D 0.025 0.038 0.635 0.965
E 0.048 0.055 1.219 1.397
G 0.067 BSC 1.702 BSC
H 0.087 0.112 2.210 2.845

J 0.015 0.025 0.381 0.635

K 1.020 1.065 25.908 27.051

L 0.320 0.365 8.128 9.271
Q 0.140 0.153 3.556 3.886
U 0.105 0.117 2.667 2.972
S 0.543 0.582 13.792 14.783

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH.

3. DIMENSION D DOES NOT INCLUDE
INTERCONNECT BAR (DAMBAR) PROTRUSION.
DIMENSION D INCLUDING PROTRUSION SHALL
NOT EXCEED 10.92 (0.043) MAXIMUM.

V

Q

K

F

U

A

B

G

–P–

M

0.10 (0.254) PMT

5X J

M

0.24 (0.610) T

OPTIONAL
CHAMFER

S

L

W

E

C

H

N

–T–

SEATING
PLANE

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH.

3. DIMENSION D DOES NOT INCLUDE
INTERCONNECT BAR (DAMBAR) PROTRUSION.
DIMENSION D INCLUDING PROTRUSION SHALL
NOT EXCEED 0.043 (1.092) MAXIMUM.

DIM MIN MAX MIN MAX

MILLIMETERSINCHES

A 0.572 0.613 14.529 15.570
B 0.390 0.415 9.906 10.541
C 0.170 0.180 4.318 4.572
D 0.025 0.038 0.635 0.965
E 0.048 0.055 1.219 1.397
F 0.850 0.935 21.590 23.749
G 0.067 BSC 1.702 BSC
H 0.166 BSC 4.216 BSC
J 0.015 0.025 0.381 0.635
K 0.900 1.100 22.860 27.940
L 0.320 0.365 8.128 9.271
N 0.320 BSC 8.128 BSC
Q 0.140 0.153 3.556 3.886
S ––– 0.620 ––– 15.748
U 0.468 0.505 11.888 12.827
V ––– 0.735 ––– 18.669
W 0.090 0.110 2.286 2.794

5X D

LM2575

25

MOTOROLA ANALOG IC DEVICE DATA

D2T SUFFIX

PLASTIC PACKAGE

CASE 936A–02

(D

2

PAK)

ISSUE A

OUTLINE DIMENSIONS

5 REF

A

123

K

B

S

H

D

G

C

E

M

L

P

N

R

V

U

TERMINAL 6

NOTES:

1 DIMENSIONING AND TOLERANCING PER ANSI

Y14.5M, 1982.
2 CONTROLLING DIMENSION: INCH.
3 TAB CONTOUR OPTIONAL WITHIN DIMENSIONS

A AND K.
4 DIMENSIONS U AND V ESTABLISH A MINIMUM

MOUNTING SURFACE FOR TERMINAL 6.
5 DIMENSIONS A AND B DO NOT INCLUDE MOLD

FLASH OR GATE PROTRUSIONS. MOLD FLASH

AND GATE PROTRUSIONS NOT TO EXCEED

0.025 (0.635) MAXIMUM.

DIMAMIN MAX MIN MAX

MILLIMETERS

0.386 0.403 9.804 10.236

INCHES

B 0.356 0.368 9.042 9.347
C 0.170 0.180 4.318 4.572
D 0.026 0.036 0.660 0.914

E 0.045 0.055 1.143 1.397

G 0.067 BSC 1.702 BSC

H 0.539 0.579 13.691 14.707
K 0.050 REF 1.270 REF
L 0.000 0.010 0.000 0.254

M 0.088 0.102 2.235 2.591

N 0.018 0.026 0.457 0.660
P 0.058 0.078 1.473 1.981
R 5 REF
S 0.116 REF 2.946 REF
U 0.200 MIN 5.080 MIN
V 0.250 MIN 6.350 MIN

__

45

M

0.010 (0.254) T

–T–

OPTIONAL
CHAMFER

LM2575

26

MOTOROLA ANALOG IC DEVICE DATA

Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty , representation or guarantee regarding
the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation consequential or incidental damages. “T ypical” parameters which may be provided in Motorola
data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals”
must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of
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applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury
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USA/EUROPE/Locations Not Listed: Motorola Literature Distribution; JAPAN: Nippon Motorola Ltd.: SPD, Strategic Planning Office, 4–32–1,

P.O. Box 5405, Denver, Colorado 80217. 303–675–2140 or 1–800–441–2447 Nishi–Gotanda, Shinagawa–ku, Tokyo 141, Japan. 81–3–5487–8488
Mfax: [e-mail] – TOUCHTONE 602–244–6609 ASIA/P ACIFIC: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park,

– US & Canada ONLY 1–800–774–1848 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852–26629298

INTERNET: http://motorola.com/sps

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LM2575/D