CAT4134

© 2006 Catalyst Semiconductor, Inc.

9

Doc. No. 5021 Rev. A

Characteristics subject to change without notice.

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

LED CURRENT SETTING

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:

LED current = 1800 x 1.2V / RFLASH

Movie Mode

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.

Table 1. Resistor Selection in Movie and Flash Mode

Movie Mode

Flash Mode

LED Current

(mA)

RSET

(kΩ)

LED Current

(mA)

RFLASH

(kΩ)

5

86.4

50

43.2

10

43.2

75

28.8

20

21.6

100

21.6

30

14.4

150

14.4

Shutdown 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.

EN

FLASH

LED1, LED2

Current

movie

mode

movie

mode

flash

mode