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

							Order this document by LM2575/D
							LM2575
	Easy	Switcher		1.0	A
	Step-Down		Voltage		Regulator	EASY SWITCHER
	The LM2575 series of regulators are monolithic integrated circuits ideally					1.0 A STEP±DOWN
						VOLTAGE REGULATOR
	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						SEMICONDUCTOR
	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.						TECHNICAL DATA
	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 efficiency					T SUFFIX
	is significantly	higher in comparison		with popular	three±terminal linear
						PLASTIC PACKAGE
	regulators, especially with higher input voltages. In many cases, the power
						CASE 314D		1
	dissipated by the LM2575 regulator is so low, that no heatsink is required or
	its size could be reduced dramatically.							5
	The LM2575 features include a guaranteed ±4% tolerance on output					Pin 1.	Vin
	voltage within specified input voltages and output load conditions, and ±10%					2.	Output
	on the oscillator frequency (±2% over 0°C to 125°C). External shutdown is					3.	Ground
						4.	Feedback
	included, featuring 80 μA typical standby current. The output switch includes
						5. ON/OFF
	cycle±by±cycle current limiting, as well as thermal shutdown for full
	protection under fault conditions.
	Features					TV SUFFIX
	• 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions							1
						PLASTIC PACKAGE
	• Adjustable Version Output Voltage Range of 1.23 V to 37 V ±4%					CASE 314B		5
	Maximum Over Line and Load Conditions					Heatsink surface
	• Guaranteed 1.0 A Output Current
						connected to Pin 3.

•Wide Input Voltage Range: 4.75 V to 40 V

•Requires Only 4 External Components

	• 52 kHz Fixed Frequency Internal Oscillator	D2T SUFFIX
		PLASTIC PACKAGE
	• TTL Shutdown Capability, Low Power Standby Mode			1
		CASE 936A
	• High Efficiency	(D2PAK)		5
	• Uses Readily Available Standard Inductors
	• Thermal Shutdown and Current Limit Protection	Heatsink surface (shown as terminal 6 in case outline
	Applications	drawing) is connected to Pin 3.
	• Simple and High±Efficiency Step±Down (Buck) Regulators	DEVICE TYPE/NOMINAL OUTPUT VOLTAGE
	• Efficient Pre±Regulator for Linear Regulators
		LM2575±3.3		3.3 V
	• On±Card Switching Regulators
		LM2575±5		5.0 V
	• Positive to Negative Converters (Buck±Boost)	LM2575±12		12 V
	• Negative Step±Up Converters	LM2575±15		15 V
		LM2575±Adj		1.23 V to 37 V
	• Power Supply for Battery Chargers
		ORDERING INFORMATION
			Operating
		Device	Temperature Range Package
		LM2575T±**		Straight Lead
		LM2575TV±**	TJ = ±40° to +125°C Vertical Mount
		LM2575D2T±**		Surface Mount
		** = Voltage Option, ie. 3.3, 5.0, 12, 15 V and
		Adjustable Output.
		Motorola, Inc. 1999		Rev 2, 07/1999

LM2575

Figure 1. Block Diagram and Typical Application

Typical Application (Fixed Output Voltage Versions)

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

			Feedback
	LM2575		4	L1
				330 μH
			Output
			2	D1	Cout
3	Gnd	5	ON/OFF	1N5819
					330 μF

5.0 V Regulated

Output 1.0 A Load

Representative Block Diagram and Typical Application

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

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		Vin	45	V
			±	±0.3 V ≤ V ≤ +Vin	V
	ON/OFF Pin Input Voltage
	Output Voltage to Ground (Steady±State)		±	±1.0	V
	Power Dissipation
	Case 314B and 314D (TO±220, 5±Lead)		PD	Internally Limited	W
	Thermal Resistance, Junction±to±Ambient		RθJA	65	°C/W
	Thermal Resistance, Junction±to±Case		RθJC	5.0	°C/W
	Case 936A (D2PAK)		PD	Internally Limited	W
	Thermal Resistance, Junction±to±Ambient		RθJA	70	°C/W
	(Figure 34)
	Thermal Resistance, Junction±to±Case		RθJC	5.0	°C/W
	Storage Temperature Range		Tstg	±65 to +150	°C
	Minimum ESD Rating (Human Body Model: C		±	3.0	kV
	= 100 pF, R = 1.5 kΩ)
	Lead Temperature (Soldering, 10 s)		±	260	°C
	Maximum Junction Temperature		TJ	150	°C

NOTE: ESD data available upon request.

2	MOTOROLA ANALOG IC DEVICE DATA

LM2575

OPERATING RATINGS (Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.)

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

SYSTEM PARAMETERS ([Note 1] Test Circuit Figure 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. ILoad = 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, ILoad = 0.2 A, TJ = 25°C)	Vout	3.234	3.3	3.366	V
Output Voltage (4.75 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)	Vout				V
TJ = 25°C		3.168	3.3	3.432
TJ = ±40 to +125°C		3.135	±	3.465
Efficiency (Vin = 12 V, ILoad = 1.0 A)	η	±	75	±	%
LM2575±5 ([Note 1] Test Circuit Figure 14)
Output Voltage (Vin = 12 V, ILoad = 0.2 A, TJ = 25°C)	Vout	4.9	5.0	5.1	V
Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)	Vout				V
TJ = 25°C		4.8	5.0	5.2
TJ = ±40 to +125°C		4.75	±	5.25
Efficiency (Vin = 12 V, ILoad = 1.0 A)	η	±	77	±	%
LM2575±12 ([Note 1] Test Circuit Figure 14)
Output Voltage (Vin = 25 V, ILoad = 0.2 A, TJ = 25°C)	Vout	11.76	12	12.24	V
Output Voltage (15 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)	Vout				V
TJ = 25°C		11.52	12	12.48
TJ = ±40 to +125°C		11.4	±	12.6
Efficiency (Vin = 15V, ILoad = 1.0 A)	η	±	88	±	%
LM2575±15 ([Note 1] Test Circuit Figure 14)
Output Voltage (Vin = 30 V, ILoad = 0.2 A, TJ = 25°C)	Vout	14.7	15	15.3	V
Output Voltage (18 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A)	Vout				V
TJ = 25°C		14.4	15	15.6
TJ = ±40 to +125°C		14.25	±	15.75
Efficiency (Vin = 18 V, ILoad = 1.0 A)	η	±	88	±	%
LM2575 ADJUSTABLE VERSION ([Note 1] Test Circuit Figure 14)
Feedback Voltage (Vin = 12 V, ILoad = 0.2 A, Vout = 5.0 V, TJ = 25°C)	VFB	1.217	1.23	1.243	V
Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.2 A ≤ ILoad ≤ 1.0 A, Vout = 5.0 V)	VFB				V
TJ = 25°C		1.193	1.23	1.267
TJ = ±40 to +125°C		1.18	±	1.28
Efficiency (Vin = 12 V, ILoad = 1.0 A, Vout = 5.0 V)	η	±	77	±	%

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

Tlow = ±40°C

Thigh = +125°C

MOTOROLA ANALOG IC DEVICE DATA	3

LM2575

DEVICE PARAMETERS

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

the 12 V version, and Vin = 30 V for the 15 V version. ILoad = 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 (Vout = 5.0 V [Adjustable Version Only])						Ib				nA
		TJ = 25°C						±	25	100
		TJ = ±40 to +125°C						±	±	200
	Oscillator Frequency [Note 3]						fosc				kHz
		TJ = 25°C						±	52	±
		TJ = 0 to +125°C						47	±	58
		TJ = ±40 to +125°C						42	±	63
	Saturation Voltage (Iout = 1.0 A [Note 4])						Vsat				V
		TJ = 25°C						±	1.0	1.2
		TJ = ±40 to +125°C						±	±	1.3
	Max Duty Cycle (ªonº) [Note 5]						DC	94	98	±	%
	Current Limit (Peak Current [Notes 4 and 3])						ICL				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						IL				mA
		Output = 0 V						±	0.8	2.0
		Output = ±1.0 V						±	6.0	20
	Quiescent Current [Note 6]						IQ				mA
		TJ = 25°C						±	5.0	9.0
		TJ = ±40 to +125°C						±	±	11
	Standby Quiescent Current						Istby				μA
					(ON/OFF Pin = 5.0 V (ªoffº))
		TJ = 25°C						±	80	200
		TJ = ±40 to +125°C						±	±	400
											V
	ON/OFF Pin Logic Input Level (Test Circuit Figure 14)
		Vout = 0 V					VIH
		TJ = 25°C						2.2	1.4	±
		TJ = ±40 to +125°C						2.4	±	±
		Vout = Nominal Output Voltage					VIL
		TJ = 25°C						±	1.2	1.0
		TJ = ±40 to +125°C						±	±	0.8
											μA
	ON/OFF Pin Input Current (Test Circuit Figure 14)
							I	±	15	30
		ON/OFF Pin = 5.0 V (ªoffº), T = 25°C
					J		IH
		ON/OFF Pin = 0 V (ªonº), T = 25°C					I	±	0	5.0
				J			IL

NOTES: 3. The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%.

4.Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to output pin.

5.Feedback (Pin 4) removed from output and connected to 0 V.

6.Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and 5.0 V versions, and +25 V for the 12 V and 15 V versions, to force the output transistor ªoffº.

7.Vin = 40 V.

4	MOTOROLA ANALOG IC DEVICE DATA

LM2575

TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 14)

Figure 2. Normalized Output Voltage

Figure 3. Line Regulation

Vout, OUTPUT VOLTAGE CHANGE (%)

0.6

Vin = 20 V

ILoad = 200 mA 0.4 Normalized at

TJ = 25°C

0.2

0

±0.2

±0.4

±0.6	±25	0	25	50	75	100	125
±50

TJ, JUNCTION TEMPERATURE (°C)

Vout, OUTPUT VOLTAGE CHANGE (%)

1.0

ILoad = 200 mA

0.8TJ = 25°C

0.63.3 V, 5.0 V and Adj

0.2
0					12 V and 15 V
±0.20	5.0	10	15	20	25	30	35	40
			Vin, INPUT VOLTAGE (V)

Vsat , SATURATION VOLTAGE (V)

Figure 4. Switch Saturation Voltage

1.2
1.1
1.0
0.9
		±40°C
0.8
		25°C
0.7
0.6
		125°C
0.5
0.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

SWITCH CURRENT (A)

IO, OUTPUT CURRENT (A)

Figure 5. Current Limit

3.0

2.5

2.0

1.5

1.0

0.5

Vin = 25 V

0

±50	±25	0	25	50	75	100	125
		TJ, JUNCTION TEMPERATURE (°C)

Figure 6. Dropout Voltage

Figure 7. Quiescent Current

	2.0
DIFFERENTIAL(V)	1.8						Vout = 5%	CURRENTQUIESCENT(mA)
		ILoad = 1.0 A					Rind = 0.2 Ω
	1.6
	1.4
INPUT±OUTPUT	1.2
	1.0	ILoad = 200 mA						I
	0.8							,
	0.6							Q
	0.4	±25	0	25	50	75	100	125
	±50
			TJ, JUNCTION TEMPERATURE (°C)

20
														Vout =	5.0 V
18														Measured at
16														Ground Pin
														°
														TJ = 25 C
14
								ILoad	= 1.0 A
12
10
								ILoad	= 200 mA
8.0
6.0
4.0
		5.0		10		15		20		25		30		35		40
0

Vin, INPUT VOLTAGE (V)

MOTOROLA ANALOG IC DEVICE DATA	5

LM2575

Istby, STANDBY QUIESCENT CURRENT (μ A)

		Figure 8. Standby Quiescent Current
120
		TJ = 25	°C
100
80
60
40
20
0
0		5.0		10		15		20		25		30		35		40

Vin, INPUT VOLTAGE (V)

Istby, STANDBY QUIESCENT CURRENT (μA)

Figure 9. Standby Quiescent Current

120

Vin = 12 V

VON/OFF = 5.0 V

100

80

60

40

20

0	±25	0	25	50	75	100	125
±50

TJ, JUNCTION TEMPERATURE (°C)

Figure 10. Oscillator Frequency

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

Figure 12. Switching Waveforms

OUTPUT	10 V
VOLTAGE	0
(PIN 2)
OUTPUT	1.0 A
CURRENT
(PIN 2)	0
INDUCTOR 1.0 A
CURRENT 0.5 A
OUTPUT	20 mV
RIPPLE	/DIV
VOLTAGE
	5.0 μs/DIV

Figure 11. Feedback Pin Current

(nA)	40	Adjustable
		Version		Only
CURRENTPIN
	0
FEEDBACK,	20
	±20
FB
I
	±40
			±25		0		25		50		75		100		125
	±50

TJ, JUNCTION TEMPERATURE (°C)

	OUTPUTVOLTAGE	Figure 13. Load Transient Response
		100
		0
		(mV)CHANGE
	,	±100
	out
	V
	(A)
	CURRENT	1.0
		0.5
	, LOAD	0
	Load	100 μs/DIV
	I

6	MOTOROLA ANALOG IC DEVICE DATA

LM2575

Figure 14. Typical Test Circuit

5.0 Output Voltage Versions

					Feedback
		Vin			4			Vout
			LM2575±5		L1
+		1			330 μH			Regulated
					Output			Output
					2
Vin		3	Gnd	5	ON/OFF
Unregulated	Cin	μF/50 V			D1	Cout
DC Input	100					330	μF	Load
8.0 V ± 40 V					1N5819	/16 V
±

Adjustable Output Voltage Versions

Feedback

Vin

LM2575

4

Vout

L1

+

1

Adjustable

330 μH

Regulated

Output

Output

2

Unregulated

3

Gnd

5

ON/OFF

Cin

Cout

R2

DC Input

100

μF/50 V

D1

330 μF

8.0 V ± 40 V

Load

1N5819

/16 V

R1

±

Vout + V

ref

1 )

R2

R1

R2 + R1

Vout

± 1

Vref

Where Vref = 1.23 V, R1

between 1.0 kΩ and 5.0 kΩ

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.

MOTOROLA ANALOG IC DEVICE DATA	7

				LM2575
				PIN FUNCTION DESCRIPTION
Pin			Symbol	Description (Refer to Figure 1)
1	Vin			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 Vsat 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				It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total
		ON/OFF
				input supply current to approximately 80 μA. The 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 ªonº condition.
				DESIGN PROCEDURE

Buck Converter Basics

The LM2575 is a ªBuckº 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:

IL(on) +	Vin ± Vout ton
	L

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

IL(off) +	Vout ± VD toff
	L

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

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

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

d + Vout Vin

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

Figure 16. Buck Converter Idealized Waveforms

Von(SW)

	Figure 15. Basic Buck Converter
	Power	L
	Switch		Vout
V	D1	Cout	RLoad
in

The next period is the ªoffº period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by 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:

	Voltage	Power		Power	Power
		Switch	Power	Switch	Switch
		Off		Off	On
	Diode
			Switch
			On
					Time

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

8	MOTOROLA ANALOG IC DEVICE DATA

LM2575

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:

Given Parameters:

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

Vout = 5.0 V

Vin(max) = Maximum DC Input Voltage

Vin(max) = 20 V

ILoad(max) = Maximum Load Current

ILoad(max) = 0.8 A

1.

Controller IC Selection

1.

Controller IC Selection

According to the required input voltage, output voltage and

According to the required input voltage, output voltage, current

current, select the appropriate type of the controller IC output

polarity and current value, use the LM2575±5 controller IC

voltage version.

2. Input Capacitor Selection (Cin)

2. Input Capacitor Selection (Cin)

To prevent large voltage transients from appearing at the input

A 47 μF, 25 V aluminium electrolytic capacitor located near to

and for stable operation of the converter, an aluminium or

the input and ground pins provides sufficient bypassing.

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.

3. Catch Diode Selection (D1)

3. Catch Diode Selection (D1)

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

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

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

fast recovery diodes shown in the Table 4.

1.25 times the maximum input voltage.

4.

Inductor Selection (L1)

4.

Inductor Selection (L1)

A. According to the required working conditions, select the

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

correct inductor value using the selection guide from

Figures 17 to 21.

B. From the appropriate inductor selection guide, identify the

B. From the selection guide, the inductance area intersected

inductance region intersected by the Maximum Input

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

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

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

manufacturers part numbers listed in Table 1 or Table 2.

Table 2, choose an inductor from any of the listed

When using Table 2 for selecting the right inductor the

manufacturers.

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:

V ±V

ton

Ip(max) + ILoad(max) )

in

out

2L

where ton is the ªonº time of the power switch and

ton +

Vout

x

1

V

in

f

osc

For additional information about the inductor, see the

inductor section in the ªExternal Componentsº section of

this data sheet.

MOTOROLA ANALOG IC DEVICE DATA	9