LP3954 Datasheet, PDF (19/60 Pages) National Semiconductor (TI) – Advanced Lighting Management Unit

LP3954
www.ti.com
SNVS340D – JUNE 2005 – REVISED MARCH 2013
SINGLE PROGRAM
If control bit LOOP=0 the program will start from Command 1 and run to either last command or to empty “0000
0000 / 0000 0000” command.
COMMAND 1
LOOP=0
ADDRESS 50H
ADDRESS 51H
COMMAND 2
ADDRESS 52H
ADDRESS 53H
COMMAND 3
ADDRESS 54H
ADDRESS 55H
IF 0000 0000 and 0000 0000 then Æ STOP
0 00 00
0 00 00
00 0
00 0
start
stop
The LEDs maintain the brightness of the last command when the single program stops. Changes in command
register will not be effective in this phase. The RGB_START bit has to be toggled off and on to make changes
effective.
START BIT
Pattern_gen_ctrl register’s RGB_START bit will enable command execution starting from Command 1.
Pattern gen ctrl register (11H)
rgb_start
Bit 2
loop
Bit 1
log
Bit 0
0 – Pattern generator disabled
1 – execution pattern starting from command 1
0 – pattern generator loop disabled (single pattern)
1 – pattern generator loop enabled (execute until stopped)
0 – color intensity mode 0
1 – color intensity mode 1
HARDWARE ON/OFF CONTROL AND DIMMING
PWM_LED input can be used as direct ON/OFF control or PWM dimming control for selected RGB outputs or
the WLED groups. PWM_LED control can be enabled with the control bits in the Ext. PWM Control register.
Audio Synchronization
The color LEDs connected to RGB outputs can be synchronized to incoming audio with Audio Synchronization
feature. Audio Sync has 2 modes. Amplitude mode synchronizes color LEDs based on input signal’s peak
amplitude. In the amplitude mode the user can select between 3 different amplitude mapping modes and 4
different speed configurations. The frequency mode synchronizes the color LEDs based on bass, middle and
treble amplitudes (= low pass, band pass and high pass filters). User can select between 2 different frequency
responses and 4 different speed configurations for best audio-visual user experience. Programmable gain and
AGC function are also available for adjustment of input signal amplitude to light response. The Audio Sync
functionality is described more closely below.
USING A DIGITAL PWM AUDIO SIGNAL AS AN AUDIO SYNCHRONIZATION SOURCE
If the input signal is a PWM signal, use a first or second order low pass filter to convert the digital PWM audio
signal into an analog waveform. There are two parameters that need to be known to get the filter to work
successfully: frequency of the PWM signal and the voltage level of the PWM signal. Suggested cut-off frequency
(-3dB) should be around 2 kHz to 4 kHz and the stop-band attenuation at sampling frequency should be around -
48dB or better. Use a resistor divider to reduce the digital signal amplitude to meet the specification of the analog
audio input. Because a low-order low-pass filter attenuates the high-frequency components from audio signal,
MODE_CONTROL=[01] selection is recommended when frequency synchronization mode is enabled.
Application example 5 shows an example of a second order RC-filter for 29 kHz PWM signal with 3.3V
amplitude. Active filters, such as a Sallen-Key filter, may also be applied. An active filter gives better stop-band
attenuation and cut-off frequency can be higher than for a RC-filter.
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