LM3553 Datasheet, PDF (8/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
BLOCK DIAGRAM
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OVP
V_IN
M/F
VIO
SCL
SDA
OVP
THERMAL
SHUTDOWN
VREF
LM3553
RESET/GPIO
I²C INTERFACE/
CONTROL LOGIC/
REGISTERS
SW
SW
Driver
SWITCH
CONTROLLER
OSC
RAMP
CURRENT
LIMIT
gm
¦
MIN. Dx
+
VOLTAGE
R_Z
-
0.35V or
SELECT
0.450V
C_C
D1
I_STEP CTRL
TORCH CTRL
FLASH CTRL
TIME-OUT CTRL
Current
Control _D1
Current
Sink
D2
D2
Current
Sink
Tx
F_EN
GND
R_SET
Circuit Description
CIRCUIT COMPONENTS
F_EN Pin
The flash enable pin, F_EN, provides an external method (non-I²C) for starting the flash pulse. When F_EN is pulled
high, logic '1', the flash current level defined through the I2C interface, will be delived to the Flash LED. If the F_EN
pin is driven low during the flash pulse, the flash event will stop. In the event that F_EN is not pulled low during the
flash pulse, the LM3553 will continue to deliver the flash current until the safety timer duration (set through the
I2C interface) is reached.
The LM3553 does not provide a fixed off-time after the flash pulse has ended. Most flash LED manufacturers
require that the flash pulse duration be 10% of the total Flash cycle. Example: If the flash pulse duration is set to
be 200 milliseconds (Flash Duration Code= 0011), the recommended off time for the LED would be 1.8 seconds.
Please consult the LED manufacturers datasheet for exact timing requirements.
If the LM3553 is placed in indicator mode or torch mode through the I²C interface and the F_EN pin is pulled high
and then low, at the end of the flash event, the LM3553 will return to the mode stored in the General Purpose
Register.
It is recommended that an external pull-down be placed between the F_EN pin and GND to prevent unwanted LED
flashing during system start-up due to unknown control logic states.
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