1 / fPWM

R1

G1

B1

R2

G2

B2

R3

G3

B3

R4

G4

B4

17

LP55281

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SNVS458D – JUNE 2007 – REVISED OCTOBER 2016

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Each RGB set has equivalent internal PWM timing between R, G, and B: R has a fixed start time, G has a fixed

mid-pulse time, and B has a fixed-pulse end time. PWM start time for each RGB set is different in order to

minimize the instantaneous current loading due to the current sink switch on transition. See Figure 12 for details.

Figure 12. Timing Diagram

7.3.3 Audio Synchronization

The ALED output can be synchronized to incoming audio with an audio-synchronization feature. Audio

synchronization synchronizes ALED based on the peak amplitude of the input signal. Programmable gain and

automatic gain control function are also available for adjustment of input signal amplitude to light response.

Control of ALED brightness refreshing frequency is done with four different frequency configurations. The

digitized input signal has DC component that is removed by a digital DC-remover (–3 dB at 500 Hz). LP55281

has a 2-channel audio (stereo) input for audio synchronization, as shown in Figure 13. The inputs accept signals

in the range of 0 V to 1.6 V peak-to-peak, and these signals are mixed into a single wave so that they can be

filtered simultaneously.

LP55281 audio synchronization is mainly realized digitally, and it consists of the following signal path blocks (see

Figure 13):

•

Input buffer

•

AD converter

•

Automatic gain control (AGC) and manually programmable gain

•

Peak detector