LM3554 datasheet(22/47 Pages) TI1

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SCL

SDA_IN

SDA_OUT

t 5

t 1

t 4

t 3

SDA

Start Condition

Stop Condition

SCL

LM3554

SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016

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Device Functional Modes (continued)

At light loads the LM3554 switches over to a pulsed frequency mode operation (light load comparator enabled).

In this mode the device only switches as necessary to maintain VOUT within regulation. This mode provides a

better efficiency due to the reduction in switching losses which become a larger portion of the total power loss at

light loads.

7.5 Programming

7.5.1 I2C-Compatible Interface

7.5.1.1 Start and Stop Conditions

The LM3554 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning

and end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL is

HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master

always generates the START and STOP conditions.

Figure 38. Start and Stop Sequences

The I2C bus is considered busy after a START condition and free after a STOP condition. During data

transmission the I2C master can generate repeated START conditions. A START and a repeated START

condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock

signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. Figure 1 and Figure 39

show the SDA and SCL signal timing for the I2C-Compatible Bus. See Electrical Characteristics for timing values.

Figure 39. I2C-Compatible Timing

7.5.1.2 I2C-Compatible Chip Address

The device address for the LM3554 is 1010011 (53). After the START condition, the I2C master sends the 7-bit

address followed by an eighth bit, read or write (R/W). R/W = 0 indicates a WRITE and R/W = 1 indicates a

READ. The second byte following the device address selects the register address to which the data will be

written. The third byte contains the data for the selected register.

LM3554 Datasheet(PDF) 22 Page - Texas Instruments