LM3556_15 Datasheet, PDF (17/39 Pages) Texas Instruments – Synchronous Boost LED Flash Driver With High-Side Current Source

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LM3556
SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015
7.5 Programming
7.5.1 I²C-Compatible Interface
7.5.1.1 Data Validity
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when SCL is LOW.
SCL
SDA
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 29. Data Validity Diagram
A pullup resistor between the controller's VIO line and SDA must be greater than [(VIO – V_OL) / 3mA] to meet the
V_OL requirement on SDA. Using a larger pullup resistor results in lower switching current with slower edges, while
using a smaller pullup results in higher switching currents with faster edges.
7.5.1.2 Start and Stop Conditions
START and STOP conditions classify the beginning and the end of the I²C session. A START condition is
defined as the 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.
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 30. Start and Stop Conditions
7.5.1.3 Transferring Data
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) 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 LM3556 pulls down
the SDA line during the 9th clock pulse, signifying an acknowledge. The LM3556 generates an acknowledge
after each byte is received. There is no acknowledge created after data is read from the LM3556.
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 LM3556 7-bit address is 0x63. 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.
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