MOTOROLA LM2575TV-ADJ, LM2575TV-3.3, LM2575TV-015, LM2575TV-012, LM2575T-ADJ Datasheet

Device

Operating

Temperature Range

Package



EASY SWITCHER

1.0 A STEP–DOWN

VOLTAGE REGULATOR

ORDERING INFORMATION

LM2575T–**
LM2575TV–** TJ = –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

(D2PAK)

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

 Motorola, Inc. 1999 Rev 2, 07/1999

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

µ

F

3ON

/OFF5

Output
2

Feedback
4

D1
1N5819

C

out

330

µ

F

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

θJA

65 °C/W

Thermal Resistance, Junction–to–Case R

θJC

5.0 °C/W

Case 936A (D2PAK) P

D

Internally Limited W

Thermal Resistance, Junction–to–Ambient

(Figure 34)

R

θJA

70 °C/W

Thermal Resistance, Junction–to–Case R

θJC

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 Vin = 30 V for the 15 V version. I

Load

= 200 mA. For typical values TJ = 25°C, for min/max values TJ is the operating

junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics

Symbol Min Typ Max Unit

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

Output Voltage (Vin = 12 V, I

Load

= 0.2 A, TJ = 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 (Vin = 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 (Vin = 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
TJ = –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 (Vin = 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
TJ = –40 to +125°C 1.18 – 1.28

Efficiency (Vin = 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 Vin = 30 V for the 15 V version. I

Load

= 200 mA. For typical values TJ = 25°C, for min/max values TJ is the operating

junction temperature range that applies [Note 2], unless otherwise noted.)

Characteristics

Symbol Min Typ Max Unit

ALL OUTPUT VOLTAGE VERSIONS

Feedback Bias Current (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.Vin = 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)

Vin, 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
TJ = 25

°

C

Figure 4. Switch Saturation Voltage Figure 5. Current Limit

Figure 6. Dropout Voltage Figure 7. Quiescent Current

I

Load

= 200 mA

TJ = 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
TJ = 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)

TJ, 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

µ

F

/16 V

C

in

100

µ

F/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

µ

F

/16 V

C

in

100

µ

F/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 (Cin 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 +Vin) 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 +Vin 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.