CAT4134_08 datasheet(8/13 Pages) CATALYST

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CAT4134

Doc. No. MD-5021 Rev. B

Characteristics subject to change without notice.

DEVICE OPERATION

The device is powered from the input pin VIN. A

switching frequency of 1.2MHz is used in Movie mode,

when the FLASH input is low. Continuous LED current

up to 50mA is controlled by the RSET resistor. For

higher load current, the Flash mode is selected by

setting the FLASH input pin high. RFLASH now

controls the LED current. In flash mode, the driver

efficiency is kept high even under high load current by

using a lower switching frequency of 900kHz. In movie

mode, the higher frequency of 1.2MHz provides a lower

noise operation.

Overvoltage Protection (OVP)

To prevent the SW pin voltage from exceeding the

internal switch maximum voltage rating, an overvoltage

protection (OVP) function is supported. The OVP pin

allows to set the maximum operating voltage on the

output VOUT using external resistors R1 and R2. The

resistor ratio sets the maximum output voltage as

shown in the equation below:

R1/R2 = (VOUTMAX /1.2) - 1.2

VOUTMAX should always be higher than the total LED

forward voltage (

ΣVf) plus 1.2V. Also VOUT must be

less than

ΣVf + 8V.

ΣVf + 1.2V < VOUTMAX < ΣVf + 8V < 16V

If the overvoltage protection is not needed, then the

OVP pin should be connected to Ground. In that case,

the maximum voltage on the SW pin is set to 17V.

BLOCK DIAGRAM

Dual

Frecuency

PWM

Controller

PGND

LED2

LED1

OVP

AGND

RSET

mux

RSET

RFLASH

FLASH

VIN

VOUT

CIN

COUT

RFLASH

2 Current Sink

Regulators

Current

Setting

CAT4134 Datasheet(PDF) 8 Page - Catalyst Semiconductor

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