LTC3407A datasheet(11/22 Pages) LINER

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LTC3565

3565fb

APPLICATIONS INFORMATION

shows some typical surface mount inductors that work

well in LTC3565 applications.

Table 1. Representative Surface Mount Inductors

MANU-

FACTURER PART NUMBER

VALUE

MAXDC

CURRENT

DCR

HEIGHT

Toko

A914BYW-1R2M=P3:

D52LC

1.2μH

2.15A

44mΩ

2mm

A960AW-1R2M=P3:

D518LC

1.2μH

1.8A

46mΩ 1.8mm

DB3015C-1068AS-1R0N 1.0μH

2.1A

43mΩ 1.5mm

DB3018C-1069AS-1R0N 1.0μH

2.1A

45mΩ 1.8mm

DB3020C-1070AS-1R0N 1.0μH

2.1A

47mΩ

2mm

A914BYW-2R2M-D52LC 2.2μH

2.05A

49mΩ

2mm

A915AY-2ROM-D53LC

2.0μH

3.3A

22mΩ

3mm

Coilcraft

LPO1704-122ML

1.2μH

2.1A

80mΩ

1mm

D01608C-222

2.2μH

2.3A

70mΩ

3mm

LP01704-222M

2.2μH

2.4A

120mΩ 1mm

Sumida

CR32-1R0

1.0μH

2.1A

72mΩ

3mm

CR5D11-1R0

1.0μH

2.2A

40mΩ 1.2mm

CDRH3D14-1R2

1.2μH

2.2A

36mΩ 1.5mm

CDRH4D18C/LD-1R1

1.1μH

2.1A

24mΩ

2mm

CDRH4D28C/LD-1R0

1.0μH

3.0A

17.5mΩ 3mm

CDRH4D28C-1R1

1.1μH

3.8A

22mΩ

3mm

CDRH4D28-1R2

1.2μH

2.56A

23.6mΩ 3mm

CDRH6D12-1R0

1.0μH

2.80A

37.5mΩ 1.5mm

CDRH4D282R2

2.2μH

2.04A

23mΩ

3mm

CDC5D232R2

2.2μH

2.16A

30mΩ 2.5mm

Taiyo

Yuden

NPO3SB1ROM

1.0μH

2.6A

27mΩ 1.8mm

N06DB2R2M

2.2μH

3.2A

29mΩ 3.2mm

N05DB2R2M

2.2μH

2.9A

32mΩ 2.8mm

Murata

LQN6C2R2M04

2.2μH

3.2A

24mΩ

5mm

FDK

MIPW3226DORGM

0.9μH

1.4A

80mΩ

1mm

Catch Diode Selection

Although unnecessary in most applications, a small

improvement in efﬁciency can be obtained in a few ap-

plications by including the optional diode D1 shown in

Figure 2, which conducts when the synchronous switch

is off. When using Burst Mode operation or pulse skip

mode, the synchronous switch is turned off at a low

current and the remaining current will be carried by the

optional diode. It is important to adequately specify the

diode peak current and average power dissipation so as

not to exceed the diode ratings. The main problem with

Schottky diodes is that their parasitic capacitance reduces

the efﬁciency, usually negating the possible beneﬁts for

LTC3565 circuits. Another problem that a Schottky diode

can introduce is higher leakage current at high tempera-

tures, which could reduce the low current efﬁciency.

Remember to keep lead lengths short and observe proper

grounding (see Board Layout Considerations) to avoid ring-

ing and increased dissipation when using a catch diode.

Input Capacitor (CIN) Selection

In continuous mode, the input current of the converter is a

square wave with a duty cycle of approximately VOUT/VIN.

To prevent large voltage transients, a low equivalent series

resistance (ESR) input capacitor sized for the maximum

RMS current must be used. The maximum RMS capacitor

current is given by:

IRMS ≈ IMAX

VOUT(VIN − VOUT )

VIN

where the maximum average output current IMAX equals

the peak current minus half the peak-to-peak ripple cur-

rent, IMAX ≅ ILIM – ΔIL/2.

This formula has a maximum at VIN = 2VOUT, where

IRMS = IOUT/2. This simple worst case is commonly used

to design because even signiﬁcant deviations do not offer

much relief. Note that capacitor manufacturer’s ripple cur-

rent ratings are often based on only 2000 hours lifetime.

This makes it advisable to further derate the capacitor,

or choose a capacitor rated at a higher temperature than

required. Several capacitors may also be paralleled to meet

the size or height requirements of the design. An additional

0.1μF to 1μF ceramic capacitor is also recommended on

VIN for high frequency decoupling, when not using an all

ceramic capacitor solution.

Output Capacitor (COUT) Selection

The selection of COUT is driven by the required ESR to

minimize voltage ripple and load step transients. Typically,

once the ESR requirement is satisﬁed, the capacitance

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