TABLE 2. Suggested Inductors and Their Suppliers (Continued)

Model

Vendor

Phone

FAX

ELL6GM100M

Panasonic

714-373-7366

714-373-7323

ELL6PM100M

Panasonic

P1174.103T

Pulse

Engineering

858-674-8100

858-674-8262

P0770.103T

Pulse

Engineering

858-674-8100

858-674-8262

CDRH5D18-100

Sumida

847-956-0666

847-956-0702

CDRH4D28-100

Sumida

CDC5D23-100

Sumida

NP05D

B100M

Taiyo

Yuden

847-925-0888

847-925-0899

NP04S

B100N

Taiyo

Yuden

SLF6025T-100M1R0

TDK

847-803-6100

847-803-6296

SLF6020T-100MR90

TDK

A918CY-100M

Toko

847-297-0070

847-699-7864

A915AY-100M

Toko

For low-cost applications, an unshielded bobbin inductor is

suggested. For noise critical applications, a toroidal or

shielded-bobbin inductor should be used. A good practice is

to lay out the board with overlapping footprints of both types

for design flexibility. This allows substitution of a low-noise

toroidal inductor, in the event that noise from low-cost bobbin

models is unacceptable.

The saturation current rating is the current level beyond

which an inductor loses its inductance. Beyond this rating,

the inductor loses its ability to limit current through the PFET

switch to a ramp and allows the switch current to increase

rapidly. This can cause poor efficiency, regulation errors or

stress to DC-DC converters like the LM2608. Saturation

occurs when the magnetic flux density from current through

the windings of the inductor exceeds what the inductor’s

core material can support with energy storage in a corre-

sponding magnetic field.

TABLE 3. Suggested Capacitors and Their Suppliers

Model

Size

Vendor

Phone

FAX

22µF, X7R or X5R Ceramic Capacitor for C2 (Output Filter Capacitor)

C3225X5RIA226M

1210

TDK

847-803-6100

847-803-6296

JMK325BJ226MM

1210

Taiyo-Yuden

847-925-0888

847-925-0899

ECJ4YB0J226M

1210

Panasonic

714-373-7366

714-373-7323

GRM42-2X5R226K6.3

1210

muRata

404-436-1300

404-436-3030

10µF, 6.3V, X7R or X5R Ceramic Capacitor for C1 (Input Filter Capacitor)

C2012X5R0J106M

0805

TDK

847-803-6100

847-803-6296

JMK212BJ106MG

0805

Taiyo Yuden

847-925-0888

847-925-0899

ECJ3YB0J106K

1206

Panasonic

714-373-7366

714-373-7323

GRM40X5R106K6.3

0805

muRata

404-436-1400

404-436-3030

CAPACITOR SELECTION

Use a 10µF, 6.3V, X7R or X5R ceramic input filter capacitor

and a 22µF, X7R or X5R ceramic output filter capacitor.

These provide an optimal balance between small size, cost,

reliability and performance. Do not use Y5V ceramic capaci-

tors. Table 3 lists suggested capacitors and suppliers.

A 10µF ceramic capacitor can be used for the output filter

capacitor for smaller size in applications where the worst-

case transient load step is less than 200mA. Use of a 10µF

output capacitor trades off smaller size for an increase in

output voltage ripple, and undershoot during line and load

transient response.

The input filter capacitor supplies current to the PFET switch

of the LM2608 in the first part of each cycle and reduces

voltage ripple imposed on the input power source. The out-

put filter capacitor smoothes out current flow from the induc-

tor to the load, helps maintain a steady output voltage during

transient load changes and reduces output voltage ripple.

These capacitors must be selected with sufficient capaci-

tance and sufficiently low ESR to perform these functions.

The ESR, or equivalent series resistance, of the filter capaci-

tors is a major factor in voltage ripple.

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