CAT4137 datasheet(9/14 Pages) CATALYST

Part #	CAT4137

Description	CMOS Boost Converter - White LED Driver

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Manufacturer	CATALYST [Catalyst Semiconductor]

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9 / 14 page

CAT4137

9

Doc. No. MD-5012Rev. B

Characteristics subject to change without notice

APPLICATION INFORMATION

EXTERNAL COMPONENT SELECTION

Capacitors

The

CAT4137

only

requires

small

ceramic

capacitors of 1uF on the input and 0.22µF on the

output. The output capacitor should be rated at 30V

or greater. Under normal conditions, a 1µF input

capacitor is sufficient. For applications with higher

output power, a larger input capacitor of 2.2µF or

4.7µF may be appropriate. X5R and X7R capacitor

types are ideal due to their stability across

temperature range.

Inductor

A 22µH inductor is recommended for most of the

CAT4137

applications.

In

cases where

the

efficiency is critical, inductances with lower series

resistance are preferred. Several inductor types

from various vendors can be used. Figure 1 shows

how different inductor types affect the efficiency

across the load range.

60

70

80

90

100

5

1015

202530

LED CURRENT [mA]

SUMIDA CDRH3D16-220

MURATA LQH32CN220

PANASONIC ELJ-EA220

PANASONIC ELJ-PC220

3 LEDs

VIN = 3.6V

Figure 1. Efficiency for various inductors

Schottky Diode

The current rating of the Schottky diode must

exceed the peak current flowing through it. The

Schottky diode performance is rated in terms of its

forward voltage at a given current. In order to

achieve the best efficiency, this forward voltage

should be as low as possible. The response time is

also critical since the driver is operating at 1MHz.

Central

Semiconductor

Schottky

CMDSH2-3

(200mA rated) or the CMDSH-3 (100mA rated) is

recommended for most applications.

LED Current Setting

The LED current is set by the external resistor

between the feedback pin (FB) and ground. The

formula below gives the relationship between the

resistor and the current:

R1 = 0.3V/LED current

LED current (mA)

R1 (Ω)

5

60

10

30

15

20

15

25

12

30

10

Table 1. Resistor R1 and LED current

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CAT4137 Datasheet(PDF) 9 Page - Catalyst Semiconductor

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