Inductor Selection

The MAX8607 is designed to use a 2.2µH inductor. To

prevent core saturation, ensure that the inductor-satura-

tion current rating exceeds the peak inductor current

for the application. Calculate the worst-case peak

inductor current with the following formula:

Table 2 provides a list of suggested inductors.

Capacitor Selection

Bypass the input to PGND using a ceramic capacitor.

Place the capacitor as close to the IC as possible. The

exact value of the input capacitor is not critical. The

typical value for the input capacitor is 10µF; however,

larger value capacitors can be used to reduce input

ripple at the expense of size and higher cost.

The output capacitance required depends on the

required LED current. A 10µF ceramic capacitor works

well in most situations, but a 4.7µF capacitor is accept-

able for load current below 300mA.

PC Board Layout

Due to fast switching waveforms and high-current paths,

careful PC board layout is required. Connect GND

directly to the exposed paddle underneath the IC; con-

nect the exposed paddle to the PC board ground plane.

Connect LGND and PGND to the ground plane. The out-

put bypass capacitor should be placed as close to the

COMP to GND as close to the IC as possible. Minimize

trace lengths between the IC and the inductor, the input

capacitor, and the output capacitor; keep these traces

connected to PGND. The traces from the input to the

inductor and from the output capacitor to the LED may

be longer. A sample layout is available in the MAX8607

evaluation kit (MAX8607EVKIT) to speed design.

Chip Information

PROCESS: BiCMOS

I

VI

V

Vs

H

PEAK

LED MAX

IN MIN

IN MIN

=

×

×

+

×

×

5

09

05

22 2

()

()

()

.

.

.

µ

µ

1MHz PWM Boost Converter for 1.5A

White LED Camera Flash

8

_______________________________________________________________________________________

LX

PGND

LGND

COMP

FLSH

MOV

OUT

EN1

EN2

LED

INPUT

2.7V TO 5.5V

OUTS

GND

MODE-

SELECT

INPUTS

C2

10

µF

L1

2.2

µH

MAX8607

EP

R2

R1

5

4

2

3

1

C3

0.1

µF

C1

10

µF

9, 10

11, 12

13

14

7

6

8

D1

U1

Figure 2. Typical Application Circuit

MANUFACTURER

SERIES

INDUCTANCE

(µH)

DCR

(m

Ω)

(A)

DIMENSIONS

Coilcraft

LPO3310

2.2

150

1.1

3.3 x 3.3 x 1.0 = 11mm

3

Cooper (Coiltronics)

SD3114

2.2

83

1.48

3.0 x 3.0 x 1.45 = 13mm

3

MIPF2520

2.2

80

0.7

2.5 x 2.0 x 1.0 = 5mm

3

FDK

MIPW3226

2.2

100

1.1

3.2 x 2.6 x 1.0 = 8mm

3

DE2812C

2.2

70

1.6

3.0 x 2.8 x 1.2 = 10mm

3

TOKO

FDSE0312

2.2

160

2.3

3.0 x 3.0 x 1.2 = 11mm

3

Table 2. Suggested Inductors