CAT4134 Datasheet, PDF (8/13 Pages) Catalyst Semiconductor – 500mA Dual Channel Movie/Flash LED Driver

CAT4134
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 = (VOUT_MAX /1.2) - 1.2
VOUT_MAX 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
VIN
C_IN
VOUT
C_OUT
SW
VIN
EN
FLASH
RFLASH
Dual
Frecuency
PWM
Controller
PGND
LED1
LED2
R1
OVP
RFLASH
RSET
Current
mux
Setting
2 Current Sink
Regulators
R2
RSET
AGND
Doc. No. 5021 Rev. A
8
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice.