CAT4134

http://onsemi.com

8

Device Operation

The device is powered from the input pin VIN. A

switching frequency of 1.2 MHz is used in Movie mode,

when the FLASH input is low. Continuous LED current up

to 50 mA 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

900 kHz. In movie mode, the higher frequency of 1.2 MHz

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 +

1.2

* 1.2

forward voltage (

SVf) plus 1.2 V. Also VOUT must be less

than

SVf + 8 V.

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 17 V.

Block Diagram

Dual

Frequency

PWM

Controller

SW

PGND

LED2

LED1

OVP

AGND

RSET

mux

RSET

RFLASH

FLASH

EN

VIN

VIN

VOUT

RFLASH

R1

R2

2 Current Sink

Regulators

Current

Setting

Figure 15. Block Diagram