LM3553 Datasheet, PDF (9/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
www.ti.com
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
T_X Pin
The transmission pin (T_X) can be used to limit the current drawn from the battery during a PA transmission.
When the T_X pin is driven high (logic '1') during a flash pulse, the LM3553 will switch to the programmed torch
current level. Once the T_X pin is driven low (logic '0'), the LM3553 will return to the flash current if this event
occurs within the original flash duration.
It is recommended that an external pull-down be placed between the T_X pin and GND to prevent unwanted LED
flashing during system start-up due to unknown control logic states.
M/F Pin
The multi-function pin (M/F) can be configured to provide hardware RESET or a general purpose input/output
(GPIO). All functionality is programmed through the I²C compatible interface and set in the M/F pin functionality
control register (address 0x20). The default function is a RESET, where a logic '1' places the part in the normal
operating mode, and a logic '0' places the part into a RESET state. A reset condition will place all LM3553
registers into their default states.
Connection Diagram
TX PA
PP/PC
SDA
SCL
Tx
LM3553
FEN
Imager
Figure 15. Typical System Configuration
I²C Compatible Interface
DATA VALIDITY
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, the state
of the data line can only be changed when CLK is LOW.
SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 16. Data Validity Diagram
A pull-up resistor between VIO and SDA must be greater than [(VIO-V_OL) / 3.7mA] to meet the V_OL requirement
on SDA. Using a larger pull-up resistor results in lower switching current with slower edges, while using a smaller
pull-up results in higher switching currents with faster edges.
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