5

LT1613

OPERATIO

LAYOUT

The LT1613 switches current at high speed, mandating

careful attention to layout for proper performance.

You

will not get advertised performance with careless layouts.

Figure 2 shows recommended component placement for

a boost (step-up) converter. Follow this closely in your

PCB layout. Note the direct path of the switching loops.

Input capacitor C1

must be placed close (< 5mm) to the IC

oscillation.

The ground terminal of output capacitor C2 should tie

close to Pin 2 of the LT1613. Doing this reduces dI/dt in the

ground copper which keeps high frequency spikes to a

minimum. The DC/DC converter ground should tie to the

PC board ground plane at one place only, to avoid intro-

ducing dI/dt in the ground plane.

A SEPIC (single-ended primary inductance converter)

schematic is shown in Figure 3. This converter topology

produces a regulated output voltage that spans (i.e., can

be higher or lower than) the output. Recommended com-

ponent placement for a SEPIC is shown in Figure 4.

D1

1613 F02

GROUND

VIAS TO

GROUND

PLANE

SHUTDOWN

L1

R2

R1

+

C2

+

C1

15

2

34

Figure 2. Recommended Component Placement for Boost

Converter. Note Direct High Current Paths Using Wide PCB

Traces. Minimize Area at Pin 3 (FB). Use Vias to Tie Local

Ground Into System Ground Plane. Use Vias at Location Shown

to Avoid Introducing Switching Currents Into Ground Plane

5V/150mA

1613 F03

SW

L1A

22

µH

L1B

22

µH

D1

GND

LT1613

C1, C2: AVX TAJA156M016

C3: TAIYO YUDEN JMK325BJ226MM

D1: MOTOROLA MBR0520

L1, L2: MURATA LQH3C220

R2

32.4k

R1

100k

C3

1

µF

FB

SHDN

C1

15

µF

4V TO

7V

+

C2

15

µF

+

SHDN

Figure 3. Single-Ended Primary Inductance Converter (SEPIC)

Generates 5V from An Input Voltage Above or Below 5V

D1

C3

1613 F04

GROUND

VIAS TO

GROUND

PLANE

SHUTDOWN

L1A

L1B

R2

R1

+

C2

+

C1

15

2

34

Figure 4. Recommended Component Placement for SEPIC

COMPONENT SELECTION

Inductors

Inductors used with the LT1613 should have a saturation

current rating (where inductance is approximately 70% of

zero current inductance) of approximately 0.5A or greater.

DCR of the inductors should be 0.5

Ω or less. For boost

converters, inductance should be 4.7

µH for input voltage

less than 3.3V and 10

µH for inputs above 3.3V. When

using the device as a SEPIC, either a coupled inductor or

two separate inductors can be used. If using separate

inductors, 22

µH units are recommended for input voltage

above 3.3V. Coupled inductors have a beneficial mutual

inductance, so a 10

µH coupled inductor results in the

same ripple current as two 20

µH uncoupled units.