LP3943 Datasheet, PDF (6/13 Pages) National Semiconductor (TI) – RGB/White/Blue 16-LED Fun Light Driver

Application Notes
THEORY OF OPERATION
The LP3943 takes incoming data from the baseband con-
troller and feeds them into several registers that control the
frequency and the duty cycle of the LEDs. Two prescaler
registers and two PWM registers provide two individual rates
to dim or blink the LEDs (for more information on these
registers, refer to Table 1. LP3943 REGISTER TABLE).
Each LED can be programmed in one of four states — on,
off, DIM0 rate or DIM1 rate. Two read-only registers provide
status on all 16 LEDs. The LP3943 can be used to drive
RGB LEDs and/or single-color LEDs to create a colorful,
entertaining, and informative setting. Alternatively, it can also
drive RGB LED as a flashlight. This is particularly suitable for
accessory functions in cellular phones and toys. Any LED
pins not used to drive LED can be used for General Purpose
Parallel Input/Output (GPIO) expansion.
The LP3943 is equipped with Power-On Reset that holds the
chip in a reset state until V_DD reaches V_POR during power up.
Once V_POR is achieved, the LP3943 comes out of reset and
initializes itself to the default state.
To bring the LP3943 into reset, hold the RST pin LOW for a
period of TW. This will put the chip into its default state. The
LP3943 can only be programmed after RST signal is HIGH
again.
I²C 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 CLK is LOW.
FIGURE 1. I²C Data Validity
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I²C START AND STOP CONDITIONS
START and STOP bits classify the beginning and the end of
the I²C session. START condition is defined as SDA signal
transitioning from HIGH to LOW while SCL line is HIGH.
STOP condition is defined as the SDA transitioning from
LOW to HIGH while SCL is HIGH. The I²C master always
generates START and STOP bits. The I²C bus is considered
to be busy after START condition and free after STOP con-
dition. During data transmission, I²C master can generate
repeated START conditions. First START and repeated
START conditions are equivalent, function-wise.
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FIGURE 2. I²C 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. The
number of bytes that can be transmitted per transfer is
unrestricted. Each byte of data has to be followed by an
acknowledge bit. The acknowledge related clock pulse is
generated by the master. The transmitter releases the SDA
line (HIGH) during the acknowledge clock pulse. The re-
ceiver must pull down the SDA line during the 9th clock
pulse, signifying an acknowledge. A receiver which has been
addressed must generate an acknowledge after each byte
has been received.
After the START condition, a chip address is sent by the I²C
master. This address is seven bits long followed by an eighth
bit which is a data direction bit (R/W). The LP3943 hardwires
bits 7 to 4 and leaves bits 3 to 1 selectable, as shown in
Figure 3. For the eighth bit, a “0” indicates a WRITE and a
“1” indicates a READ. The LP3943 supports only a WRITE
during chip addressing. 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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