LB2012B220M datasheet(2/14 Pages) SAMHOP

2 / 14 page

GENERAL DESCRIPTION

The SM8237 is a step-up DC/DC converter

specifically designed to drive white LEDs with a

constant current. The device can drive two, three

or four LEDs in series from a Li-ion cell. Series

connection of the LEDs provides identical LED

currents resulting in uniform brightness and

eliminating the need for ballast resistors. The

SM8237 switches at 1.2 MHz, allowing the use of

tiny external components. The output capacitor can

be as small as 0.22μF, saving space and cost

versus alternative solutions. A low 95mV feedback

voltage minimizes power loss in the current setting

resistor for better efficiency.

FEATURES

* Inherently matched LED current

* High efficiency : 84% typical

* Drives up to four LEDs from a 2.8V supply

* Drives up to six LEDs from a 5V supply

* 36V rugged bipolar switch

* Fast 1.2MHz switching frequency

* Uses tiny 1 mm tall inductors

* Requires only 0.22μF output capacitor

* Low profile TSOT package

SAMHOP Microelectronics Corp.

1.2MHz STEP-UP CONVERTER

TYPICAL APPLICATION

C1 , C2 : X7R Dielectric

D1 : Frontier electronics SS14

L1 : Frontier electronics CSS0218P-22ON-LFR

4.80

4.85

4.90

4.95

5.00

5.05

5.10

5.15

5.20

1020304050 60708090 100 105

OUTPUT CURRENT (mA)

Page 1

V.1.3 Aug 28,2007

100

1020 3040 506070 80 90 100 105

OUTPUT CURRINT (mA)

OUTPUT VOLTAGE vs. LOAD CURRENT

EFFICIENCY vs. LOAD CURRENT

Output Current (mA)

Vin = 3.3V

Vout = 5V

Output Current (mA)

SM8237

Vin

GND

22 uH

51 K

1 uf

Vout

5V / 100 mA

1 K

4.7 uf

Vin

3.3 V

OFF ON

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