CAT4134
APPLICATION INFORMATION
The typical application for the CAT4134 is in a
camera-equipped cellular phone where the LEDs are
used for illumination in flash mode with short duration
high-current pulse and in movie mode with continuous
lighter load. In movie mode, the FLASH pin is set low.
Note:
Hot-plugging the LEDs while the output is fully charged is not
recommended. If the LEDs are disconnected, the device should first
be powered-down and the output discharged before reconnecting
the LEDs to the output and the LED pins.
TIMING DIAGRAM
EN
FLASH
LED1, LED2
Current
flash
mode
movie
mode
movie
mode
LED CURRENT SETTING
Flash Mode
Table 1. Resistor Selection in Movie and Flash Mode
The enable EN and FLASH logic input signals control
the LED current. When both the EN and FLASH
inputs are high, the driver is in flash or strobe mode.
In this mode, the LED1 and LED2 pin currents are set
by the resistor RFLASH and are regulated to 1800
times the current in the RFLASH resistor and follows
the equation:
Movie Mode
Flash Mode
LED Current RSET
LED Current RFLASH
(mA)
5
(kΩ)
86.4
43.2
21.6
14.4
(mA)
(kΩ)
43.2
28.8
21.6
14.4
50
10
75
20
100
150
30
LED current = 1800 x 1.2V / RFLASH
Shutdown Mode
Movie Mode
When the EN input is low, the driver is in shutdown
mode and there is no current flowing in either LED1 or
LED2 pins.
When the EN input is high and FLASH is low, the
driver is in movie mode. In this mode, the LED1 and
LED2 pin currents are set by the resistor RSET and
are regulated to 360 times the current in the RSET
resistor and follows the equation:
LED current = 360 x 1.2V / RSET
Table 1 lists the various LED currents and the asso-
ciated resistor values in movie and flash modes.
© 2006 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice.
9
Doc. No. 5021 Rev. A
CATALYST [ CATALYST SEMICONDUCTOR ]
