LM27965 Datasheet, PDF (10/23 Pages) National Semiconductor (TI) – Dual Display White LED Driver with I2C Compatible Brightness Control

LM27965
SNVS380B – MAY 2006 – REVISED FEBRUARY 2013
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SCL
SDIO
data
change
allowed
data
valid
data
change
allowed
data
valid
data
change
allowed
Figure 10. Data Validity Diagram
A pull-up resistor between VIO and SDIO must be greater than [(VIO-V_OL) / 3mA] to meet the V_OL requirement
on SDIO. 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.
START AND STOP CONDITIONS
START and STOP conditions classify the beginning and the end of the I²C session. A START condition is
defined as SDIO signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as
the SDIO 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.
SDIO
SCL
S
START condition
P
STOP condition
Figure 11. Start and Stop Conditions
TRANSFERING DATA
Every byte put on the SDIO 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 SDIO line (HIGH) during the acknowledge clock pulse. The LM27965 pulls
down the SDIO line during the 9th clock pulse, signifying an acknowledge. The LM27965 generates an
acknowledge after each byte is 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 LM27965 address is 36h (38h for -M version). 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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