LM26 datasheet(15/19 Pages) NSC

15 / 19 page

Application Information

SETTING THE OUTPUT VOLTAGE

The LM2612 features pin-selectable output voltage to elimi-

nate the need for external feedback resistors. Select an

output voltage of 1.05V, 1.3V, 1.5V or 1.8V by configuring the

VID0 and VID1 pins, as directed in Table 1.

TABLE 1. VID0 and VID1 Output Voltage Selection Settings

OUT (V)

Logic Level

VID0

VID1

1.8

1.5

1.3

1.05

VID0 and VID1 are digital inputs. They may be set high by

connecting to VDD or low by connecting to SGND. Option-

ally, VID0 and VID1 may be driven by digital gates that

provide over 1.3V for a high state and less than 0.4V for a

low state to ensure valid logic levels. The VID0 and VID1

inputs each have an internal 1.8 µA pull-down that pulls them

low for a default 1.5V output when left unconnected. Leaving

these pins open is acceptable, but setting the pins high or

low is recommended.

INDUCTOR SELECTION

A 10µH inductor with a saturation current rating greater than

the max current limit of the device is recommended for most

applications. The inductor’s resistance should be less than

0.3

Ω for good efficiency. Table 2 lists suggested inductors

and suppliers.

TABLE 2. Suggested Inductors and Their Suppliers

Model

Vendor

Phone

FAX

DO1608C-103

Coilcraft

847-639-6400

847-639-1469

DO1606T-103

Coilcraft

UP1B-100

Coiltronics

561-241-7876

561-241-9339

UP0.4CB-100

Coiltronics

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 LM2612. 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.

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