Soft start is implemented by ramping up the internal refer-

ence in the LM2612 to gradually increase the output voltage.

The reference ramps up in about 400µs. When powering up

in PWM mode, soft start may take an additional 200us to

allow time for the error amplifier compensation network to

charge.

Thermal Overload Protection

The LM2612 has a thermal overload protection function that

operates to protect itself from short-term misuse and over-

load conditions. When the junction temperature exceeds

about 155˚C, the device initiates a soft-start cycle which is

completed after the temperature drops below 130˚C. Pro-

longed operation in thermal overload conditions may dam-

age the device and is considered bad practice.

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

V

Logic Level

VID0

VID1

1.8

0

1

1.5

0

0

1.5

N.C.

N.C.

1.3

1

0

1.05

1

1

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 1.2V 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. Leav-

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

low is recommended.

Inductor Selection

A 10µH inductor with a saturation current rating over 850mA

(980mA for B grade) 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

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 looses it’s inductance. Beyond this rating,

the inductor looses it’s 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. Satu-

ration occurs when the magnetic flux density from current

through the windings of the inductor exceeds what the in-

ductor’s core material can support with energy storage in a

corresponding 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

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