LM3553 Datasheet, PDF (10/26 Pages) National Semiconductor (TI) – 1.2A Dual Flash LED Driver System with I2C Compatible

LM3553
SNVS414B – FEBRUARY 2008 – REVISED MAY 2013
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START AND STOP CONDITIONS
START and STOP conditions classify the beginning and the end of the I²C session. A START condition is
defined as SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as
the SDA transitioning from LOW to HIGH while SCL is HIGH. The I²C master always generates START and
STOP conditions. The I²C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I²C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise. 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.
SDA
SCL
S
START condition
P
STOP condition
Figure 17. Start and Stop Conditions
TRANSFERRING DATA
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) being transferred first.
Each byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated
by the master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM3553 pulls
down the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3553 generates an
acknowledge after each byte has been received.
After the START condition, the I²C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM3553 address is 53h. For the eighth bit, a “0” indicates a
WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The
third byte contains data to write to the selected register.
ack from slave
ack from slave
ack from slave
start msb Chip Address lsb w ack msb Register Add lsb ack msb DATA lsb ack stop
SCL
SDA
start
Id = 53h
w ack
addr = 10h
ack
w = write (SDA = "0")
ack = acknowledge (SDA pulled down by the slave)
id = chip address, 53h for LM3553
Figure 18. Write Cycle
I²C COMPATIBLE CHIP ADDRESS
The chip address for LM3553 is 1010011, or 53hex.
data = 08h
ack stop
10
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